Create releng/7.2 from stable/7 in preparation for 7.2-RELEASE.

[FreeBSD/releng/7.2.git] / lib / libc / stdlib / malloc.c

/*-
 * Copyright (C) 2006-2008 Jason Evans <jasone@FreeBSD.org>.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice(s), this list of conditions and the following disclaimer as
 *    the first lines of this file unmodified other than the possible
 *    addition of one or more copyright notices.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice(s), this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
 * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 *******************************************************************************
 *
 * This allocator implementation is designed to provide scalable performance
 * for multi-threaded programs on multi-processor systems.  The following
 * features are included for this purpose:
 *
 *   + Multiple arenas are used if there are multiple CPUs, which reduces lock
 *     contention and cache sloshing.
 *
 *   + Cache line sharing between arenas is avoided for internal data
 *     structures.
 *
 *   + Memory is managed in chunks and runs (chunks can be split into runs),
 *     rather than as individual pages.  This provides a constant-time
 *     mechanism for associating allocations with particular arenas.
 *
 * Allocation requests are rounded up to the nearest size class, and no record
 * of the original request size is maintained.  Allocations are broken into
 * categories according to size class.  Assuming runtime defaults, 4 kB pages
 * and a 16 byte quantum on a 32-bit system, the size classes in each category
 * are as follows:
 *
 *   |=====================================|
 *   | Category | Subcategory    |    Size |
 *   |=====================================|
 *   | Small    | Tiny           |       2 |
 *   |          |                |       4 |
 *   |          |                |       8 |
 *   |          |----------------+---------|
 *   |          | Quantum-spaced |      16 |
 *   |          |                |      32 |
 *   |          |                |      48 |
 *   |          |                |     ... |
 *   |          |                |     480 |
 *   |          |                |     496 |
 *   |          |                |     512 |
 *   |          |----------------+---------|
 *   |          | Sub-page       |    1 kB |
 *   |          |                |    2 kB |
 *   |=====================================|
 *   | Large                     |    4 kB |
 *   |                           |    8 kB |
 *   |                           |   12 kB |
 *   |                           |     ... |
 *   |                           | 1012 kB |
 *   |                           | 1016 kB |
 *   |                           | 1020 kB |
 *   |=====================================|
 *   | Huge                      |    1 MB |
 *   |                           |    2 MB |
 *   |                           |    3 MB |
 *   |                           |     ... |
 *   |=====================================|
 *
 * A different mechanism is used for each category:
 *
 *   Small : Each size class is segregated into its own set of runs.  Each run
 *           maintains a bitmap of which regions are free/allocated.
 *
 *   Large : Each allocation is backed by a dedicated run.  Metadata are stored
 *           in the associated arena chunk header maps.
 *
 *   Huge : Each allocation is backed by a dedicated contiguous set of chunks.
 *          Metadata are stored in a separate red-black tree.
 *
 *******************************************************************************
 */

/*
 * MALLOC_PRODUCTION disables assertions and statistics gathering.  It also
 * defaults the A and J runtime options to off.  These settings are appropriate
 * for production systems.
 */
#define MALLOC_PRODUCTION

#ifndef MALLOC_PRODUCTION
   /*
    * MALLOC_DEBUG enables assertions and other sanity checks, and disables
    * inline functions.
    */
#  define MALLOC_DEBUG

   /* MALLOC_STATS enables statistics calculation. */
#  define MALLOC_STATS
#endif

/*
 * MALLOC_BALANCE enables monitoring of arena lock contention and dynamically
 * re-balances arena load if exponentially averaged contention exceeds a
 * certain threshold.
 */
#define MALLOC_BALANCE

/*
 * MALLOC_DSS enables use of sbrk(2) to allocate chunks from the data storage
 * segment (DSS).  In an ideal world, this functionality would be completely
 * unnecessary, but we are burdened by history and the lack of resource limits
 * for anonymous mapped memory.
 */
#define MALLOC_DSS

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include "libc_private.h"
#ifdef MALLOC_DEBUG
#  define _LOCK_DEBUG
#endif
#include "spinlock.h"
#include "namespace.h"
#include <sys/mman.h>
#include <sys/param.h>
#include <sys/stddef.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/sysctl.h>
#include <sys/uio.h>
#include <sys/ktrace.h> /* Must come after several other sys/ includes. */

#include <machine/cpufunc.h>
#include <machine/vmparam.h>

#include <errno.h>
#include <limits.h>
#include <pthread.h>
#include <sched.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>

#include "un-namespace.h"

#ifdef MALLOC_DEBUG
#  ifdef NDEBUG
#    undef NDEBUG
#  endif
#else
#  ifndef NDEBUG
#    define NDEBUG
#  endif
#endif
#include <assert.h>

#include "rb.h"

#ifdef MALLOC_DEBUG
   /* Disable inlining to make debugging easier. */
#  define inline
#endif

/* Size of stack-allocated buffer passed to strerror_r(). */
#define STRERROR_BUF            64

/* Minimum alignment of allocations is 2^QUANTUM_2POW_MIN bytes. */
#ifdef __i386__
#  define QUANTUM_2POW_MIN      4
#  define SIZEOF_PTR_2POW       2
#  define CPU_SPINWAIT          __asm__ volatile("pause")
#endif
#ifdef __ia64__
#  define QUANTUM_2POW_MIN      4
#  define SIZEOF_PTR_2POW       3
#endif
#ifdef __alpha__
#  define QUANTUM_2POW_MIN      4
#  define SIZEOF_PTR_2POW       3
#  define NO_TLS
#endif
#ifdef __sparc64__
#  define QUANTUM_2POW_MIN      4
#  define SIZEOF_PTR_2POW       3
#  define NO_TLS
#endif
#ifdef __amd64__
#  define QUANTUM_2POW_MIN      4
#  define SIZEOF_PTR_2POW       3
#  define CPU_SPINWAIT          __asm__ volatile("pause")
#endif
#ifdef __arm__
#  define QUANTUM_2POW_MIN      3
#  define SIZEOF_PTR_2POW       2
#  define NO_TLS
#endif
#ifdef __mips__
#  define QUANTUM_2POW_MIN      3
#  define SIZEOF_PTR_2POW       2
#  define NO_TLS
#endif
#ifdef __powerpc__
#  define QUANTUM_2POW_MIN      4
#  define SIZEOF_PTR_2POW       2
#endif

#define SIZEOF_PTR              (1U << SIZEOF_PTR_2POW)

/* sizeof(int) == (1U << SIZEOF_INT_2POW). */
#ifndef SIZEOF_INT_2POW
#  define SIZEOF_INT_2POW       2
#endif

/* We can't use TLS in non-PIC programs, since TLS relies on loader magic. */
#if (!defined(PIC) && !defined(NO_TLS))
#  define NO_TLS
#endif

#ifdef NO_TLS
   /* MALLOC_BALANCE requires TLS. */
#  ifdef MALLOC_BALANCE
#    undef MALLOC_BALANCE
#  endif
#endif

/*
 * Size and alignment of memory chunks that are allocated by the OS's virtual
 * memory system.
 */
#define CHUNK_2POW_DEFAULT      20

/* Maximum number of dirty pages per arena. */
#define DIRTY_MAX_DEFAULT       (1U << 9)

/*
 * Maximum size of L1 cache line.  This is used to avoid cache line aliasing,
 * so over-estimates are okay (up to a point), but under-estimates will
 * negatively affect performance.
 */
#define CACHELINE_2POW          6
#define CACHELINE               ((size_t)(1U << CACHELINE_2POW))

/* Smallest size class to support. */
#define TINY_MIN_2POW           1

/*
 * Maximum size class that is a multiple of the quantum, but not (necessarily)
 * a power of 2.  Above this size, allocations are rounded up to the nearest
 * power of 2.
 */
#define SMALL_MAX_2POW_DEFAULT  9
#define SMALL_MAX_DEFAULT       (1U << SMALL_MAX_2POW_DEFAULT)

/*
 * RUN_MAX_OVRHD indicates maximum desired run header overhead.  Runs are sized
 * as small as possible such that this setting is still honored, without
 * violating other constraints.  The goal is to make runs as small as possible
 * without exceeding a per run external fragmentation threshold.
 *
 * We use binary fixed point math for overhead computations, where the binary
 * point is implicitly RUN_BFP bits to the left.
 *
 * Note that it is possible to set RUN_MAX_OVRHD low enough that it cannot be
 * honored for some/all object sizes, since there is one bit of header overhead
 * per object (plus a constant).  This constraint is relaxed (ignored) for runs
 * that are so small that the per-region overhead is greater than:
 *
 *   (RUN_MAX_OVRHD / (reg_size << (3+RUN_BFP))
 */
#define RUN_BFP                 12
/*                                    \/   Implicit binary fixed point. */
#define RUN_MAX_OVRHD           0x0000003dU
#define RUN_MAX_OVRHD_RELAX     0x00001800U

/* Put a cap on small object run size.  This overrides RUN_MAX_OVRHD. */
#define RUN_MAX_SMALL_2POW      15
#define RUN_MAX_SMALL           (1U << RUN_MAX_SMALL_2POW)

/*
 * Hyper-threaded CPUs may need a special instruction inside spin loops in
 * order to yield to another virtual CPU.  If no such instruction is defined
 * above, make CPU_SPINWAIT a no-op.
 */
#ifndef CPU_SPINWAIT
#  define CPU_SPINWAIT
#endif

/*
 * Adaptive spinning must eventually switch to blocking, in order to avoid the
 * potential for priority inversion deadlock.  Backing off past a certain point
 * can actually waste time.
 */
#define SPIN_LIMIT_2POW         11

/*
 * Conversion from spinning to blocking is expensive; we use (1U <<
 * BLOCK_COST_2POW) to estimate how many more times costly blocking is than
 * worst-case spinning.
 */
#define BLOCK_COST_2POW         4

#ifdef MALLOC_BALANCE
   /*
    * We use an exponential moving average to track recent lock contention,
    * where the size of the history window is N, and alpha=2/(N+1).
    *
    * Due to integer math rounding, very small values here can cause
    * substantial degradation in accuracy, thus making the moving average decay
    * faster than it would with precise calculation.
    */
#  define BALANCE_ALPHA_INV_2POW        9

   /*
    * Threshold value for the exponential moving contention average at which to
    * re-assign a thread.
    */
#  define BALANCE_THRESHOLD_DEFAULT     (1U << (SPIN_LIMIT_2POW-4))
#endif

/******************************************************************************/

/*
 * Mutexes based on spinlocks.  We can't use normal pthread spinlocks in all
 * places, because they require malloc()ed memory, which causes bootstrapping
 * issues in some cases.
 */
typedef struct {
        spinlock_t      lock;
} malloc_mutex_t;

/* Set to true once the allocator has been initialized. */
static bool malloc_initialized = false;

/* Used to avoid initialization races. */
static malloc_mutex_t init_lock = {_SPINLOCK_INITIALIZER};

/******************************************************************************/
/*
 * Statistics data structures.
 */

#ifdef MALLOC_STATS

typedef struct malloc_bin_stats_s malloc_bin_stats_t;
struct malloc_bin_stats_s {
        /*
         * Number of allocation requests that corresponded to the size of this
         * bin.
         */
        uint64_t        nrequests;

        /* Total number of runs created for this bin's size class. */
        uint64_t        nruns;

        /*
         * Total number of runs reused by extracting them from the runs tree for
         * this bin's size class.
         */
        uint64_t        reruns;

        /* High-water mark for this bin. */
        unsigned long   highruns;

        /* Current number of runs in this bin. */
        unsigned long   curruns;
};

typedef struct arena_stats_s arena_stats_t;
struct arena_stats_s {
        /* Number of bytes currently mapped. */
        size_t          mapped;

        /*
         * Total number of purge sweeps, total number of madvise calls made,
         * and total pages purged in order to keep dirty unused memory under
         * control.
         */
        uint64_t        npurge;
        uint64_t        nmadvise;
        uint64_t        purged;

        /* Per-size-category statistics. */
        size_t          allocated_small;
        uint64_t        nmalloc_small;
        uint64_t        ndalloc_small;

        size_t          allocated_large;
        uint64_t        nmalloc_large;
        uint64_t        ndalloc_large;

#ifdef MALLOC_BALANCE
        /* Number of times this arena reassigned a thread due to contention. */
        uint64_t        nbalance;
#endif
};

typedef struct chunk_stats_s chunk_stats_t;
struct chunk_stats_s {
        /* Number of chunks that were allocated. */
        uint64_t        nchunks;

        /* High-water mark for number of chunks allocated. */
        unsigned long   highchunks;

        /*
         * Current number of chunks allocated.  This value isn't maintained for
         * any other purpose, so keep track of it in order to be able to set
         * highchunks.
         */
        unsigned long   curchunks;
};

#endif /* #ifdef MALLOC_STATS */

/******************************************************************************/
/*
 * Extent data structures.
 */

/* Tree of extents. */
typedef struct extent_node_s extent_node_t;
struct extent_node_s {
#ifdef MALLOC_DSS
        /* Linkage for the size/address-ordered tree. */
        rb_node(extent_node_t) link_szad;
#endif

        /* Linkage for the address-ordered tree. */
        rb_node(extent_node_t) link_ad;

        /* Pointer to the extent that this tree node is responsible for. */
        void    *addr;

        /* Total region size. */
        size_t  size;
};
typedef rb_tree(extent_node_t) extent_tree_t;

/******************************************************************************/
/*
 * Arena data structures.
 */

typedef struct arena_s arena_t;
typedef struct arena_bin_s arena_bin_t;

/* Each element of the chunk map corresponds to one page within the chunk. */
typedef struct arena_chunk_map_s arena_chunk_map_t;
struct arena_chunk_map_s {
        /*
         * Linkage for run trees.  There are two disjoint uses:
         *
         * 1) arena_t's runs_avail tree.
         * 2) arena_run_t conceptually uses this linkage for in-use non-full
         *    runs, rather than directly embedding linkage.
         */
        rb_node(arena_chunk_map_t)      link;

        /*
         * Run address (or size) and various flags are stored together.  The bit
         * layout looks like (assuming 32-bit system):
         *
         *   ???????? ???????? ????---- ---kdzla
         *
         * ? : Unallocated: Run address for first/last pages, unset for internal
         *                  pages.
         *     Small: Run address.
         *     Large: Run size for first page, unset for trailing pages.
         * - : Unused.
         * k : key?
         * d : dirty?
         * z : zeroed?
         * l : large?
         * a : allocated?
         *
         * Following are example bit patterns for the three types of runs.
         *
         * r : run address
         * s : run size
         * x : don't care
         * - : 0
         * [dzla] : bit set
         *
         *   Unallocated:
         *     ssssssss ssssssss ssss---- --------
         *     xxxxxxxx xxxxxxxx xxxx---- ----d---
         *     ssssssss ssssssss ssss---- -----z--
         *
         *   Small:
         *     rrrrrrrr rrrrrrrr rrrr---- -------a
         *     rrrrrrrr rrrrrrrr rrrr---- -------a
         *     rrrrrrrr rrrrrrrr rrrr---- -------a
         *
         *   Large:
         *     ssssssss ssssssss ssss---- ------la
         *     -------- -------- -------- ------la
         *     -------- -------- -------- ------la
         */
        size_t                          bits;
#define CHUNK_MAP_KEY           ((size_t)0x10U)
#define CHUNK_MAP_DIRTY         ((size_t)0x08U)
#define CHUNK_MAP_ZEROED        ((size_t)0x04U)
#define CHUNK_MAP_LARGE         ((size_t)0x02U)
#define CHUNK_MAP_ALLOCATED     ((size_t)0x01U)
};
typedef rb_tree(arena_chunk_map_t) arena_avail_tree_t;
typedef rb_tree(arena_chunk_map_t) arena_run_tree_t;

/* Arena chunk header. */
typedef struct arena_chunk_s arena_chunk_t;
struct arena_chunk_s {
        /* Arena that owns the chunk. */
        arena_t         *arena;

        /* Linkage for the arena's chunks_dirty tree. */
        rb_node(arena_chunk_t) link_dirty;

        /* Number of dirty pages. */
        size_t          ndirty;

        /* Map of pages within chunk that keeps track of free/large/small. */
        arena_chunk_map_t map[1]; /* Dynamically sized. */
};
typedef rb_tree(arena_chunk_t) arena_chunk_tree_t;

typedef struct arena_run_s arena_run_t;
struct arena_run_s {
#ifdef MALLOC_DEBUG
        uint32_t        magic;
#  define ARENA_RUN_MAGIC 0x384adf93
#endif

        /* Bin this run is associated with. */
        arena_bin_t     *bin;

        /* Index of first element that might have a free region. */
        unsigned        regs_minelm;

        /* Number of free regions in run. */
        unsigned        nfree;

        /* Bitmask of in-use regions (0: in use, 1: free). */
        unsigned        regs_mask[1]; /* Dynamically sized. */
};

struct arena_bin_s {
        /*
         * Current run being used to service allocations of this bin's size
         * class.
         */
        arena_run_t     *runcur;

        /*
         * Tree of non-full runs.  This tree is used when looking for an
         * existing run when runcur is no longer usable.  We choose the
         * non-full run that is lowest in memory; this policy tends to keep
         * objects packed well, and it can also help reduce the number of
         * almost-empty chunks.
         */
        arena_run_tree_t runs;

        /* Size of regions in a run for this bin's size class. */
        size_t          reg_size;

        /* Total size of a run for this bin's size class. */
        size_t          run_size;

        /* Total number of regions in a run for this bin's size class. */
        uint32_t        nregs;

        /* Number of elements in a run's regs_mask for this bin's size class. */
        uint32_t        regs_mask_nelms;

        /* Offset of first region in a run for this bin's size class. */
        uint32_t        reg0_offset;

#ifdef MALLOC_STATS
        /* Bin statistics. */
        malloc_bin_stats_t stats;
#endif
};

struct arena_s {
#ifdef MALLOC_DEBUG
        uint32_t                magic;
#  define ARENA_MAGIC 0x947d3d24
#endif

        /* All operations on this arena require that lock be locked. */
        pthread_mutex_t         lock;

#ifdef MALLOC_STATS
        arena_stats_t           stats;
#endif

        /* Tree of dirty-page-containing chunks this arena manages. */
        arena_chunk_tree_t      chunks_dirty;

        /*
         * In order to avoid rapid chunk allocation/deallocation when an arena
         * oscillates right on the cusp of needing a new chunk, cache the most
         * recently freed chunk.  The spare is left in the arena's chunk trees
         * until it is deleted.
         *
         * There is one spare chunk per arena, rather than one spare total, in
         * order to avoid interactions between multiple threads that could make
         * a single spare inadequate.
         */
        arena_chunk_t           *spare;

        /*
         * Current count of pages within unused runs that are potentially
         * dirty, and for which madvise(... MADV_FREE) has not been called.  By
         * tracking this, we can institute a limit on how much dirty unused
         * memory is mapped for each arena.
         */
        size_t                  ndirty;

        /*
         * Size/address-ordered tree of this arena's available runs.  This tree
         * is used for first-best-fit run allocation.
         */
        arena_avail_tree_t      runs_avail;

#ifdef MALLOC_BALANCE
        /*
         * The arena load balancing machinery needs to keep track of how much
         * lock contention there is.  This value is exponentially averaged.
         */
        uint32_t                contention;
#endif

        /*
         * bins is used to store rings of free regions of the following sizes,
         * assuming a 16-byte quantum, 4kB pagesize, and default MALLOC_OPTIONS.
         *
         *   bins[i] | size |
         *   --------+------+
         *        0  |    2 |
         *        1  |    4 |
         *        2  |    8 |
         *   --------+------+
         *        3  |   16 |
         *        4  |   32 |
         *        5  |   48 |
         *        6  |   64 |
         *           :      :
         *           :      :
         *       33  |  496 |
         *       34  |  512 |
         *   --------+------+
         *       35  | 1024 |
         *       36  | 2048 |
         *   --------+------+
         */
        arena_bin_t             bins[1]; /* Dynamically sized. */
};

/******************************************************************************/
/*
 * Data.
 */

/* Number of CPUs. */
static unsigned         ncpus;

/* VM page size. */
static size_t           pagesize;
static size_t           pagesize_mask;
static size_t           pagesize_2pow;

/* Various bin-related settings. */
static size_t           bin_maxclass; /* Max size class for bins. */
static unsigned         ntbins; /* Number of (2^n)-spaced tiny bins. */
static unsigned         nqbins; /* Number of quantum-spaced bins. */
static unsigned         nsbins; /* Number of (2^n)-spaced sub-page bins. */
static size_t           small_min;
static size_t           small_max;

/* Various quantum-related settings. */
static size_t           quantum;
static size_t           quantum_mask; /* (quantum - 1). */

/* Various chunk-related settings. */
static size_t           chunksize;
static size_t           chunksize_mask; /* (chunksize - 1). */
static size_t           chunk_npages;
static size_t           arena_chunk_header_npages;
static size_t           arena_maxclass; /* Max size class for arenas. */

/********/
/*
 * Chunks.
 */

/* Protects chunk-related data structures. */
static malloc_mutex_t   huge_mtx;

/* Tree of chunks that are stand-alone huge allocations. */
static extent_tree_t    huge;

#ifdef MALLOC_DSS
/*
 * Protects sbrk() calls.  This avoids malloc races among threads, though it
 * does not protect against races with threads that call sbrk() directly.
 */
static malloc_mutex_t   dss_mtx;
/* Base address of the DSS. */
static void             *dss_base;
/* Current end of the DSS, or ((void *)-1) if the DSS is exhausted. */
static void             *dss_prev;
/* Current upper limit on DSS addresses. */
static void             *dss_max;

/*
 * Trees of chunks that were previously allocated (trees differ only in node
 * ordering).  These are used when allocating chunks, in an attempt to re-use
 * address space.  Depending on function, different tree orderings are needed,
 * which is why there are two trees with the same contents.
 */
static extent_tree_t    dss_chunks_szad;
static extent_tree_t    dss_chunks_ad;
#endif

#ifdef MALLOC_STATS
/* Huge allocation statistics. */
static uint64_t         huge_nmalloc;
static uint64_t         huge_ndalloc;
static size_t           huge_allocated;
#endif

/****************************/
/*
 * base (internal allocation).
 */

/*
 * Current pages that are being used for internal memory allocations.  These
 * pages are carved up in cacheline-size quanta, so that there is no chance of
 * false cache line sharing.
 */
static void             *base_pages;
static void             *base_next_addr;
static void             *base_past_addr; /* Addr immediately past base_pages. */
static extent_node_t    *base_nodes;
static malloc_mutex_t   base_mtx;
#ifdef MALLOC_STATS
static size_t           base_mapped;
#endif

/********/
/*
 * Arenas.
 */

/*
 * Arenas that are used to service external requests.  Not all elements of the
 * arenas array are necessarily used; arenas are created lazily as needed.
 */
static arena_t          **arenas;
static unsigned         narenas;
#ifndef NO_TLS
#  ifdef MALLOC_BALANCE
static unsigned         narenas_2pow;
#  else
static unsigned         next_arena;
#  endif
#endif
static pthread_mutex_t  arenas_lock; /* Protects arenas initialization. */

#ifndef NO_TLS
/*
 * Map of pthread_self() --> arenas[???], used for selecting an arena to use
 * for allocations.
 */
static __thread arena_t *arenas_map;
#endif

#ifdef MALLOC_STATS
/* Chunk statistics. */
static chunk_stats_t    stats_chunks;
#endif

/*******************************/
/*
 * Runtime configuration options.
 */
const char      *_malloc_options;

#ifndef MALLOC_PRODUCTION
static bool     opt_abort = true;
static bool     opt_junk = true;
#else
static bool     opt_abort = false;
static bool     opt_junk = false;
#endif
#ifdef MALLOC_DSS
static bool     opt_dss = true;
static bool     opt_mmap = true;
#endif
static size_t   opt_dirty_max = DIRTY_MAX_DEFAULT;
#ifdef MALLOC_BALANCE
static uint64_t opt_balance_threshold = BALANCE_THRESHOLD_DEFAULT;
#endif
static bool     opt_print_stats = false;
static size_t   opt_quantum_2pow = QUANTUM_2POW_MIN;
static size_t   opt_small_max_2pow = SMALL_MAX_2POW_DEFAULT;
static size_t   opt_chunk_2pow = CHUNK_2POW_DEFAULT;
static bool     opt_utrace = false;
static bool     opt_sysv = false;
static bool     opt_xmalloc = false;
static bool     opt_zero = false;
static int      opt_narenas_lshift = 0;

typedef struct {
        void    *p;
        size_t  s;
        void    *r;
} malloc_utrace_t;

#define UTRACE(a, b, c)                                                 \
        if (opt_utrace) {                                               \
                malloc_utrace_t ut;                                     \
                ut.p = (a);                                             \
                ut.s = (b);                                             \
                ut.r = (c);                                             \
                utrace(&ut, sizeof(ut));                                \
        }

/******************************************************************************/
/*
 * Begin function prototypes for non-inline static functions.
 */

static void     malloc_mutex_init(malloc_mutex_t *mutex);
static bool     malloc_spin_init(pthread_mutex_t *lock);
static void     wrtmessage(const char *p1, const char *p2, const char *p3,
                const char *p4);
#ifdef MALLOC_STATS
static void     malloc_printf(const char *format, ...);
#endif
static char     *umax2s(uintmax_t x, char *s);
#ifdef MALLOC_DSS
static bool     base_pages_alloc_dss(size_t minsize);
#endif
static bool     base_pages_alloc_mmap(size_t minsize);
static bool     base_pages_alloc(size_t minsize);
static void     *base_alloc(size_t size);
static void     *base_calloc(size_t number, size_t size);
static extent_node_t *base_node_alloc(void);
static void     base_node_dealloc(extent_node_t *node);
#ifdef MALLOC_STATS
static void     stats_print(arena_t *arena);
#endif
static void     *pages_map(void *addr, size_t size);
static void     pages_unmap(void *addr, size_t size);
#ifdef MALLOC_DSS
static void     *chunk_alloc_dss(size_t size);
static void     *chunk_recycle_dss(size_t size, bool zero);
#endif
static void     *chunk_alloc_mmap(size_t size);
static void     *chunk_alloc(size_t size, bool zero);
#ifdef MALLOC_DSS
static extent_node_t *chunk_dealloc_dss_record(void *chunk, size_t size);
static bool     chunk_dealloc_dss(void *chunk, size_t size);
#endif
static void     chunk_dealloc_mmap(void *chunk, size_t size);
static void     chunk_dealloc(void *chunk, size_t size);
#ifndef NO_TLS
static arena_t  *choose_arena_hard(void);
#endif
static void     arena_run_split(arena_t *arena, arena_run_t *run, size_t size,
    bool large, bool zero);
static arena_chunk_t *arena_chunk_alloc(arena_t *arena);
static void     arena_chunk_dealloc(arena_t *arena, arena_chunk_t *chunk);
static arena_run_t *arena_run_alloc(arena_t *arena, size_t size, bool large,
    bool zero);
static void     arena_purge(arena_t *arena);
static void     arena_run_dalloc(arena_t *arena, arena_run_t *run, bool dirty);
static void     arena_run_trim_head(arena_t *arena, arena_chunk_t *chunk,
    arena_run_t *run, size_t oldsize, size_t newsize);
static void     arena_run_trim_tail(arena_t *arena, arena_chunk_t *chunk,
    arena_run_t *run, size_t oldsize, size_t newsize, bool dirty);
static arena_run_t *arena_bin_nonfull_run_get(arena_t *arena, arena_bin_t *bin);
static void *arena_bin_malloc_hard(arena_t *arena, arena_bin_t *bin);
static size_t arena_bin_run_size_calc(arena_bin_t *bin, size_t min_run_size);
#ifdef MALLOC_BALANCE
static void     arena_lock_balance_hard(arena_t *arena);
#endif
static void     *arena_malloc_large(arena_t *arena, size_t size, bool zero);
static void     *arena_palloc(arena_t *arena, size_t alignment, size_t size,
    size_t alloc_size);
static size_t   arena_salloc(const void *ptr);
static void     arena_dalloc_large(arena_t *arena, arena_chunk_t *chunk,
    void *ptr);
static void     arena_ralloc_large_shrink(arena_t *arena, arena_chunk_t *chunk,
    void *ptr, size_t size, size_t oldsize);
static bool     arena_ralloc_large_grow(arena_t *arena, arena_chunk_t *chunk,
    void *ptr, size_t size, size_t oldsize);
static bool     arena_ralloc_large(void *ptr, size_t size, size_t oldsize);
static void     *arena_ralloc(void *ptr, size_t size, size_t oldsize);
static bool     arena_new(arena_t *arena);
static arena_t  *arenas_extend(unsigned ind);
static void     *huge_malloc(size_t size, bool zero);
static void     *huge_palloc(size_t alignment, size_t size);
static void     *huge_ralloc(void *ptr, size_t size, size_t oldsize);
static void     huge_dalloc(void *ptr);
static void     malloc_print_stats(void);
static bool     malloc_init_hard(void);

/*
 * End function prototypes.
 */
/******************************************************************************/
/*
 * Begin mutex.  We can't use normal pthread mutexes in all places, because
 * they require malloc()ed memory, which causes bootstrapping issues in some
 * cases.
 */

static void
malloc_mutex_init(malloc_mutex_t *mutex)
{
        static const spinlock_t lock = _SPINLOCK_INITIALIZER;

        mutex->lock = lock;
}

static inline void
malloc_mutex_lock(malloc_mutex_t *mutex)
{

        if (__isthreaded)
                _SPINLOCK(&mutex->lock);
}

static inline void
malloc_mutex_unlock(malloc_mutex_t *mutex)
{

        if (__isthreaded)
                _SPINUNLOCK(&mutex->lock);
}

/*
 * End mutex.
 */
/******************************************************************************/
/*
 * Begin spin lock.  Spin locks here are actually adaptive mutexes that block
 * after a period of spinning, because unbounded spinning would allow for
 * priority inversion.
 */

/*
 * We use an unpublished interface to initialize pthread mutexes with an
 * allocation callback, in order to avoid infinite recursion.
 */
int     _pthread_mutex_init_calloc_cb(pthread_mutex_t *mutex,
    void *(calloc_cb)(size_t, size_t));

__weak_reference(_pthread_mutex_init_calloc_cb_stub,
    _pthread_mutex_init_calloc_cb);

int
_pthread_mutex_init_calloc_cb_stub(pthread_mutex_t *mutex,
    void *(calloc_cb)(size_t, size_t))
{

        return (0);
}

static bool
malloc_spin_init(pthread_mutex_t *lock)
{

        if (_pthread_mutex_init_calloc_cb(lock, base_calloc) != 0)
                return (true);

        return (false);
}

static inline unsigned
malloc_spin_lock(pthread_mutex_t *lock)
{
        unsigned ret = 0;

        if (__isthreaded) {
                if (_pthread_mutex_trylock(lock) != 0) {
                        unsigned i;
                        volatile unsigned j;

                        /* Exponentially back off. */
                        for (i = 1; i <= SPIN_LIMIT_2POW; i++) {
                                for (j = 0; j < (1U << i); j++) {
                                        ret++;
                                        CPU_SPINWAIT;
                                }

                                if (_pthread_mutex_trylock(lock) == 0)
                                        return (ret);
                        }

                        /*
                         * Spinning failed.  Block until the lock becomes
                         * available, in order to avoid indefinite priority
                         * inversion.
                         */
                        _pthread_mutex_lock(lock);
                        assert((ret << BLOCK_COST_2POW) != 0);
                        return (ret << BLOCK_COST_2POW);
                }
        }

        return (ret);
}

static inline void
malloc_spin_unlock(pthread_mutex_t *lock)
{

        if (__isthreaded)
                _pthread_mutex_unlock(lock);
}

/*
 * End spin lock.
 */
/******************************************************************************/
/*
 * Begin Utility functions/macros.
 */

/* Return the chunk address for allocation address a. */
#define CHUNK_ADDR2BASE(a)                                              \
        ((void *)((uintptr_t)(a) & ~chunksize_mask))

/* Return the chunk offset of address a. */
#define CHUNK_ADDR2OFFSET(a)                                            \
        ((size_t)((uintptr_t)(a) & chunksize_mask))

/* Return the smallest chunk multiple that is >= s. */
#define CHUNK_CEILING(s)                                                \
        (((s) + chunksize_mask) & ~chunksize_mask)

/* Return the smallest cacheline multiple that is >= s. */
#define CACHELINE_CEILING(s)                                            \
        (((s) + (CACHELINE - 1)) & ~(CACHELINE - 1))

/* Return the smallest quantum multiple that is >= a. */
#define QUANTUM_CEILING(a)                                              \
        (((a) + quantum_mask) & ~quantum_mask)

/* Return the smallest pagesize multiple that is >= s. */
#define PAGE_CEILING(s)                                                 \
        (((s) + pagesize_mask) & ~pagesize_mask)

/* Compute the smallest power of 2 that is >= x. */
static inline size_t
pow2_ceil(size_t x)
{

        x--;
        x |= x >> 1;
        x |= x >> 2;
        x |= x >> 4;
        x |= x >> 8;
        x |= x >> 16;
#if (SIZEOF_PTR == 8)
        x |= x >> 32;
#endif
        x++;
        return (x);
}

#ifdef MALLOC_BALANCE
/*
 * Use a simple linear congruential pseudo-random number generator:
 *
 *   prn(y) = (a*x + c) % m
 *
 * where the following constants ensure maximal period:
 *
 *   a == Odd number (relatively prime to 2^n), and (a-1) is a multiple of 4.
 *   c == Odd number (relatively prime to 2^n).
 *   m == 2^32
 *
 * See Knuth's TAOCP 3rd Ed., Vol. 2, pg. 17 for details on these constraints.
 *
 * This choice of m has the disadvantage that the quality of the bits is
 * proportional to bit position.  For example. the lowest bit has a cycle of 2,
 * the next has a cycle of 4, etc.  For this reason, we prefer to use the upper
 * bits.
 */
#  define PRN_DEFINE(suffix, var, a, c)                                 \
static inline void                                                      \
sprn_##suffix(uint32_t seed)                                            \
{                                                                       \
        var = seed;                                                     \
}                                                                       \
                                                                        \
static inline uint32_t                                                  \
prn_##suffix(uint32_t lg_range)                                         \
{                                                                       \
        uint32_t ret, x;                                                \
                                                                        \
        assert(lg_range > 0);                                           \
        assert(lg_range <= 32);                                         \
                                                                        \
        x = (var * (a)) + (c);                                          \
        var = x;                                                        \
        ret = x >> (32 - lg_range);                                     \
                                                                        \
        return (ret);                                                   \
}
#  define SPRN(suffix, seed)    sprn_##suffix(seed)
#  define PRN(suffix, lg_range) prn_##suffix(lg_range)
#endif

#ifdef MALLOC_BALANCE
/* Define the PRNG used for arena assignment. */
static __thread uint32_t balance_x;
PRN_DEFINE(balance, balance_x, 1297, 1301)
#endif

static void
wrtmessage(const char *p1, const char *p2, const char *p3, const char *p4)
{

        _write(STDERR_FILENO, p1, strlen(p1));
        _write(STDERR_FILENO, p2, strlen(p2));
        _write(STDERR_FILENO, p3, strlen(p3));
        _write(STDERR_FILENO, p4, strlen(p4));
}

void    (*_malloc_message)(const char *p1, const char *p2, const char *p3,
            const char *p4) = wrtmessage;

#ifdef MALLOC_STATS
/*
 * Print to stderr in such a way as to (hopefully) avoid memory allocation.
 */
static void
malloc_printf(const char *format, ...)
{
        char buf[4096];
        va_list ap;

        va_start(ap, format);
        vsnprintf(buf, sizeof(buf), format, ap);
        va_end(ap);
        _malloc_message(buf, "", "", "");
}
#endif

/*
 * We don't want to depend on vsnprintf() for production builds, since that can
 * cause unnecessary bloat for static binaries.  umax2s() provides minimal
 * integer printing functionality, so that malloc_printf() use can be limited to
 * MALLOC_STATS code.
 */
#define UMAX2S_BUFSIZE  21
static char *
umax2s(uintmax_t x, char *s)
{
        unsigned i;

        /* Make sure UMAX2S_BUFSIZE is large enough. */
        assert(sizeof(uintmax_t) <= 8);

        i = UMAX2S_BUFSIZE - 1;
        s[i] = '\0';
        do {
                i--;
                s[i] = "0123456789"[x % 10];
                x /= 10;
        } while (x > 0);

        return (&s[i]);
}

/******************************************************************************/

#ifdef MALLOC_DSS
static bool
base_pages_alloc_dss(size_t minsize)
{

        /*
         * Do special DSS allocation here, since base allocations don't need to
         * be chunk-aligned.
         */
        malloc_mutex_lock(&dss_mtx);
        if (dss_prev != (void *)-1) {
                intptr_t incr;
                size_t csize = CHUNK_CEILING(minsize);

                do {
                        /* Get the current end of the DSS. */
                        dss_max = sbrk(0);

                        /*
                         * Calculate how much padding is necessary to
                         * chunk-align the end of the DSS.  Don't worry about
                         * dss_max not being chunk-aligned though.
                         */
                        incr = (intptr_t)chunksize
                            - (intptr_t)CHUNK_ADDR2OFFSET(dss_max);
                        assert(incr >= 0);
                        if ((size_t)incr < minsize)
                                incr += csize;

                        dss_prev = sbrk(incr);
                        if (dss_prev == dss_max) {
                                /* Success. */
                                dss_max = (void *)((intptr_t)dss_prev + incr);
                                base_pages = dss_prev;
                                base_next_addr = base_pages;
                                base_past_addr = dss_max;
#ifdef MALLOC_STATS
                                base_mapped += incr;
#endif
                                malloc_mutex_unlock(&dss_mtx);
                                return (false);
                        }
                } while (dss_prev != (void *)-1);
        }
        malloc_mutex_unlock(&dss_mtx);

        return (true);
}
#endif

static bool
base_pages_alloc_mmap(size_t minsize)
{
        size_t csize;

        assert(minsize != 0);
        csize = PAGE_CEILING(minsize);
        base_pages = pages_map(NULL, csize);
        if (base_pages == NULL)
                return (true);
        base_next_addr = base_pages;
        base_past_addr = (void *)((uintptr_t)base_pages + csize);
#ifdef MALLOC_STATS
        base_mapped += csize;
#endif

        return (false);
}

static bool
base_pages_alloc(size_t minsize)
{

#ifdef MALLOC_DSS
        if (opt_mmap && minsize != 0)
#endif
        {
                if (base_pages_alloc_mmap(minsize) == false)
                        return (false);
        }

#ifdef MALLOC_DSS
        if (opt_dss) {
                if (base_pages_alloc_dss(minsize) == false)
                        return (false);
        }

#endif

        return (true);
}

static void *
base_alloc(size_t size)
{
        void *ret;
        size_t csize;

        /* Round size up to nearest multiple of the cacheline size. */
        csize = CACHELINE_CEILING(size);

        malloc_mutex_lock(&base_mtx);
        /* Make sure there's enough space for the allocation. */
        if ((uintptr_t)base_next_addr + csize > (uintptr_t)base_past_addr) {
                if (base_pages_alloc(csize)) {
                        malloc_mutex_unlock(&base_mtx);
                        return (NULL);
                }
        }
        /* Allocate. */
        ret = base_next_addr;
        base_next_addr = (void *)((uintptr_t)base_next_addr + csize);
        malloc_mutex_unlock(&base_mtx);

        return (ret);
}

static void *
base_calloc(size_t number, size_t size)
{
        void *ret;

        ret = base_alloc(number * size);
        memset(ret, 0, number * size);

        return (ret);
}

static extent_node_t *
base_node_alloc(void)
{
        extent_node_t *ret;

        malloc_mutex_lock(&base_mtx);
        if (base_nodes != NULL) {
                ret = base_nodes;
                base_nodes = *(extent_node_t **)ret;
                malloc_mutex_unlock(&base_mtx);
        } else {
                malloc_mutex_unlock(&base_mtx);
                ret = (extent_node_t *)base_alloc(sizeof(extent_node_t));
        }

        return (ret);
}

static void
base_node_dealloc(extent_node_t *node)
{

        malloc_mutex_lock(&base_mtx);
        *(extent_node_t **)node = base_nodes;
        base_nodes = node;
        malloc_mutex_unlock(&base_mtx);
}

/******************************************************************************/

#ifdef MALLOC_STATS
static void
stats_print(arena_t *arena)
{
        unsigned i, gap_start;

        malloc_printf("dirty: %zu page%s dirty, %llu sweep%s,"
            " %llu madvise%s, %llu page%s purged\n",
            arena->ndirty, arena->ndirty == 1 ? "" : "s",
            arena->stats.npurge, arena->stats.npurge == 1 ? "" : "s",
            arena->stats.nmadvise, arena->stats.nmadvise == 1 ? "" : "s",
            arena->stats.purged, arena->stats.purged == 1 ? "" : "s");

        malloc_printf("            allocated      nmalloc      ndalloc\n");
        malloc_printf("small:   %12zu %12llu %12llu\n",
            arena->stats.allocated_small, arena->stats.nmalloc_small,
            arena->stats.ndalloc_small);
        malloc_printf("large:   %12zu %12llu %12llu\n",
            arena->stats.allocated_large, arena->stats.nmalloc_large,
            arena->stats.ndalloc_large);
        malloc_printf("total:   %12zu %12llu %12llu\n",
            arena->stats.allocated_small + arena->stats.allocated_large,
            arena->stats.nmalloc_small + arena->stats.nmalloc_large,
            arena->stats.ndalloc_small + arena->stats.ndalloc_large);
        malloc_printf("mapped:  %12zu\n", arena->stats.mapped);

        malloc_printf("bins:     bin   size regs pgs  requests   newruns"
            "    reruns maxruns curruns\n");
        for (i = 0, gap_start = UINT_MAX; i < ntbins + nqbins + nsbins; i++) {
                if (arena->bins[i].stats.nrequests == 0) {
                        if (gap_start == UINT_MAX)
                                gap_start = i;
                } else {
                        if (gap_start != UINT_MAX) {
                                if (i > gap_start + 1) {
                                        /* Gap of more than one size class. */
                                        malloc_printf("[%u..%u]\n",
                                            gap_start, i - 1);
                                } else {
                                        /* Gap of one size class. */
                                        malloc_printf("[%u]\n", gap_start);
                                }
                                gap_start = UINT_MAX;
                        }
                        malloc_printf(
                            "%13u %1s %4u %4u %3u %9llu %9llu"
                            " %9llu %7lu %7lu\n",
                            i,
                            i < ntbins ? "T" : i < ntbins + nqbins ? "Q" : "S",
                            arena->bins[i].reg_size,
                            arena->bins[i].nregs,
                            arena->bins[i].run_size >> pagesize_2pow,
                            arena->bins[i].stats.nrequests,
                            arena->bins[i].stats.nruns,
                            arena->bins[i].stats.reruns,
                            arena->bins[i].stats.highruns,
                            arena->bins[i].stats.curruns);
                }
        }
        if (gap_start != UINT_MAX) {
                if (i > gap_start + 1) {
                        /* Gap of more than one size class. */
                        malloc_printf("[%u..%u]\n", gap_start, i - 1);
                } else {
                        /* Gap of one size class. */
                        malloc_printf("[%u]\n", gap_start);
                }
        }
}
#endif

/*
 * End Utility functions/macros.
 */
/******************************************************************************/
/*
 * Begin extent tree code.
 */

#ifdef MALLOC_DSS
static inline int
extent_szad_comp(extent_node_t *a, extent_node_t *b)
{
        int ret;
        size_t a_size = a->size;
        size_t b_size = b->size;

        ret = (a_size > b_size) - (a_size < b_size);
        if (ret == 0) {
                uintptr_t a_addr = (uintptr_t)a->addr;
                uintptr_t b_addr = (uintptr_t)b->addr;

                ret = (a_addr > b_addr) - (a_addr < b_addr);
        }

        return (ret);
}

/* Wrap red-black tree macros in functions. */
rb_wrap(__unused static, extent_tree_szad_, extent_tree_t, extent_node_t,
    link_szad, extent_szad_comp)
#endif

static inline int
extent_ad_comp(extent_node_t *a, extent_node_t *b)
{
        uintptr_t a_addr = (uintptr_t)a->addr;
        uintptr_t b_addr = (uintptr_t)b->addr;

        return ((a_addr > b_addr) - (a_addr < b_addr));
}

/* Wrap red-black tree macros in functions. */
rb_wrap(__unused static, extent_tree_ad_, extent_tree_t, extent_node_t, link_ad,
    extent_ad_comp)

/*
 * End extent tree code.
 */
/******************************************************************************/
/*
 * Begin chunk management functions.
 */

static void *
pages_map(void *addr, size_t size)
{
        void *ret;

        /*
         * We don't use MAP_FIXED here, because it can cause the *replacement*
         * of existing mappings, and we only want to create new mappings.
         */
        ret = mmap(addr, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON,
            -1, 0);
        assert(ret != NULL);

        if (ret == MAP_FAILED)
                ret = NULL;
        else if (addr != NULL && ret != addr) {
                /*
                 * We succeeded in mapping memory, but not in the right place.
                 */
                if (munmap(ret, size) == -1) {
                        char buf[STRERROR_BUF];

                        strerror_r(errno, buf, sizeof(buf));
                        _malloc_message(_getprogname(),
                            ": (malloc) Error in munmap(): ", buf, "\n");
                        if (opt_abort)
                                abort();
                }
                ret = NULL;
        }

        assert(ret == NULL || (addr == NULL && ret != addr)
            || (addr != NULL && ret == addr));
        return (ret);
}

static void
pages_unmap(void *addr, size_t size)
{

        if (munmap(addr, size) == -1) {
                char buf[STRERROR_BUF];

                strerror_r(errno, buf, sizeof(buf));
                _malloc_message(_getprogname(),
                    ": (malloc) Error in munmap(): ", buf, "\n");
                if (opt_abort)
                        abort();
        }
}

#ifdef MALLOC_DSS
static void *
chunk_alloc_dss(size_t size)
{

        /*
         * sbrk() uses a signed increment argument, so take care not to
         * interpret a huge allocation request as a negative increment.
         */
        if ((intptr_t)size < 0)
                return (NULL);

        malloc_mutex_lock(&dss_mtx);
        if (dss_prev != (void *)-1) {
                intptr_t incr;

                /*
                 * The loop is necessary to recover from races with other
                 * threads that are using the DSS for something other than
                 * malloc.
                 */
                do {
                        void *ret;

                        /* Get the current end of the DSS. */
                        dss_max = sbrk(0);

                        /*
                         * Calculate how much padding is necessary to
                         * chunk-align the end of the DSS.
                         */
                        incr = (intptr_t)size
                            - (intptr_t)CHUNK_ADDR2OFFSET(dss_max);
                        if (incr == (intptr_t)size)
                                ret = dss_max;
                        else {
                                ret = (void *)((intptr_t)dss_max + incr);
                                incr += size;
                        }

                        dss_prev = sbrk(incr);
                        if (dss_prev == dss_max) {
                                /* Success. */
                                dss_max = (void *)((intptr_t)dss_prev + incr);
                                malloc_mutex_unlock(&dss_mtx);
                                return (ret);
                        }
                } while (dss_prev != (void *)-1);
        }
        malloc_mutex_unlock(&dss_mtx);

        return (NULL);
}

static void *
chunk_recycle_dss(size_t size, bool zero)
{
        extent_node_t *node, key;

        key.addr = NULL;
        key.size = size;
        malloc_mutex_lock(&dss_mtx);
        node = extent_tree_szad_nsearch(&dss_chunks_szad, &key);
        if (node != NULL) {
                void *ret = node->addr;

                /* Remove node from the tree. */
                extent_tree_szad_remove(&dss_chunks_szad, node);
                if (node->size == size) {
                        extent_tree_ad_remove(&dss_chunks_ad, node);
                        base_node_dealloc(node);
                } else {
                        /*
                         * Insert the remainder of node's address range as a
                         * smaller chunk.  Its position within dss_chunks_ad
                         * does not change.
                         */
                        assert(node->size > size);
                        node->addr = (void *)((uintptr_t)node->addr + size);
                        node->size -= size;
                        extent_tree_szad_insert(&dss_chunks_szad, node);
                }
                malloc_mutex_unlock(&dss_mtx);

                if (zero)
                        memset(ret, 0, size);
                return (ret);
        }
        malloc_mutex_unlock(&dss_mtx);

        return (NULL);
}
#endif

static void *
chunk_alloc_mmap(size_t size)
{
        void *ret;
        size_t offset;

        /*
         * Ideally, there would be a way to specify alignment to mmap() (like
         * NetBSD has), but in the absence of such a feature, we have to work
         * hard to efficiently create aligned mappings.  The reliable, but
         * expensive method is to create a mapping that is over-sized, then
         * trim the excess.  However, that always results in at least one call
         * to pages_unmap().
         *
         * A more optimistic approach is to try mapping precisely the right
         * amount, then try to append another mapping if alignment is off.  In
         * practice, this works out well as long as the application is not
         * interleaving mappings via direct mmap() calls.  If we do run into a
         * situation where there is an interleaved mapping and we are unable to
         * extend an unaligned mapping, our best option is to momentarily
         * revert to the reliable-but-expensive method.  This will tend to
         * leave a gap in the memory map that is too small to cause later
         * problems for the optimistic method.
         */

        ret = pages_map(NULL, size);
        if (ret == NULL)
                return (NULL);

        offset = CHUNK_ADDR2OFFSET(ret);
        if (offset != 0) {
                /* Try to extend chunk boundary. */
                if (pages_map((void *)((uintptr_t)ret + size),
                    chunksize - offset) == NULL) {
                        /*
                         * Extension failed.  Clean up, then revert to the
                         * reliable-but-expensive method.
                         */
                        pages_unmap(ret, size);

                        /* Beware size_t wrap-around. */
                        if (size + chunksize <= size)
                                return NULL;

                        ret = pages_map(NULL, size + chunksize);
                        if (ret == NULL)
                                return (NULL);

                        /* Clean up unneeded leading/trailing space. */
                        offset = CHUNK_ADDR2OFFSET(ret);
                        if (offset != 0) {
                                /* Leading space. */
                                pages_unmap(ret, chunksize - offset);

                                ret = (void *)((uintptr_t)ret +
                                    (chunksize - offset));

                                /* Trailing space. */
                                pages_unmap((void *)((uintptr_t)ret + size),
                                    offset);
                        } else {
                                /* Trailing space only. */
                                pages_unmap((void *)((uintptr_t)ret + size),
                                    chunksize);
                        }
                } else {
                        /* Clean up unneeded leading space. */
                        pages_unmap(ret, chunksize - offset);
                        ret = (void *)((uintptr_t)ret + (chunksize - offset));
                }
        }

        return (ret);
}

static void *
chunk_alloc(size_t size, bool zero)
{
        void *ret;

        assert(size != 0);
        assert((size & chunksize_mask) == 0);

#ifdef MALLOC_DSS
        if (opt_mmap)
#endif
        {
                ret = chunk_alloc_mmap(size);
                if (ret != NULL)
                        goto RETURN;
        }

#ifdef MALLOC_DSS
        if (opt_dss) {
                ret = chunk_recycle_dss(size, zero);
                if (ret != NULL) {
                        goto RETURN;
                }

                ret = chunk_alloc_dss(size);
                if (ret != NULL)
                        goto RETURN;
        }
#endif

        /* All strategies for allocation failed. */
        ret = NULL;
RETURN:
#ifdef MALLOC_STATS
        if (ret != NULL) {
                stats_chunks.nchunks += (size / chunksize);
                stats_chunks.curchunks += (size / chunksize);
        }
        if (stats_chunks.curchunks > stats_chunks.highchunks)
                stats_chunks.highchunks = stats_chunks.curchunks;
#endif

        assert(CHUNK_ADDR2BASE(ret) == ret);
        return (ret);
}

#ifdef MALLOC_DSS
static extent_node_t *
chunk_dealloc_dss_record(void *chunk, size_t size)
{
        extent_node_t *node, *prev, key;

        key.addr = (void *)((uintptr_t)chunk + size);
        node = extent_tree_ad_nsearch(&dss_chunks_ad, &key);
        /* Try to coalesce forward. */
        if (node != NULL && node->addr == key.addr) {
                /*
                 * Coalesce chunk with the following address range.  This does
                 * not change the position within dss_chunks_ad, so only
                 * remove/insert from/into dss_chunks_szad.
                 */
                extent_tree_szad_remove(&dss_chunks_szad, node);
                node->addr = chunk;
                node->size += size;
                extent_tree_szad_insert(&dss_chunks_szad, node);
        } else {
                /*
                 * Coalescing forward failed, so insert a new node.  Drop
                 * dss_mtx during node allocation, since it is possible that a
                 * new base chunk will be allocated.
                 */
                malloc_mutex_unlock(&dss_mtx);
                node = base_node_alloc();
                malloc_mutex_lock(&dss_mtx);
                if (node == NULL)
                        return (NULL);
                node->addr = chunk;
                node->size = size;
                extent_tree_ad_insert(&dss_chunks_ad, node);
                extent_tree_szad_insert(&dss_chunks_szad, node);
        }

        /* Try to coalesce backward. */
        prev = extent_tree_ad_prev(&dss_chunks_ad, node);
        if (prev != NULL && (void *)((uintptr_t)prev->addr + prev->size) ==
            chunk) {
                /*
                 * Coalesce chunk with the previous address range.  This does
                 * not change the position within dss_chunks_ad, so only
                 * remove/insert node from/into dss_chunks_szad.
                 */
                extent_tree_szad_remove(&dss_chunks_szad, prev);
                extent_tree_ad_remove(&dss_chunks_ad, prev);

                extent_tree_szad_remove(&dss_chunks_szad, node);
                node->addr = prev->addr;
                node->size += prev->size;
                extent_tree_szad_insert(&dss_chunks_szad, node);

                base_node_dealloc(prev);
        }

        return (node);
}

static bool
chunk_dealloc_dss(void *chunk, size_t size)
{

        malloc_mutex_lock(&dss_mtx);
        if ((uintptr_t)chunk >= (uintptr_t)dss_base
            && (uintptr_t)chunk < (uintptr_t)dss_max) {
                extent_node_t *node;

                /* Try to coalesce with other unused chunks. */
                node = chunk_dealloc_dss_record(chunk, size);
                if (node != NULL) {
                        chunk = node->addr;
                        size = node->size;
                }

                /* Get the current end of the DSS. */
                dss_max = sbrk(0);

                /*
                 * Try to shrink the DSS if this chunk is at the end of the
                 * DSS.  The sbrk() call here is subject to a race condition
                 * with threads that use brk(2) or sbrk(2) directly, but the
                 * alternative would be to leak memory for the sake of poorly
                 * designed multi-threaded programs.
                 */
                if ((void *)((uintptr_t)chunk + size) == dss_max
                    && (dss_prev = sbrk(-(intptr_t)size)) == dss_max) {
                        /* Success. */
                        dss_max = (void *)((intptr_t)dss_prev - (intptr_t)size);

                        if (node != NULL) {
                                extent_tree_szad_remove(&dss_chunks_szad, node);
                                extent_tree_ad_remove(&dss_chunks_ad, node);
                                base_node_dealloc(node);
                        }
                        malloc_mutex_unlock(&dss_mtx);
                } else {
                        malloc_mutex_unlock(&dss_mtx);
                        madvise(chunk, size, MADV_FREE);
                }

                return (false);
        }
        malloc_mutex_unlock(&dss_mtx);

        return (true);
}
#endif

static void
chunk_dealloc_mmap(void *chunk, size_t size)
{

        pages_unmap(chunk, size);
}

static void
chunk_dealloc(void *chunk, size_t size)
{

        assert(chunk != NULL);
        assert(CHUNK_ADDR2BASE(chunk) == chunk);
        assert(size != 0);
        assert((size & chunksize_mask) == 0);

#ifdef MALLOC_STATS
        stats_chunks.curchunks -= (size / chunksize);
#endif

#ifdef MALLOC_DSS
        if (opt_dss) {
                if (chunk_dealloc_dss(chunk, size) == false)
                        return;
        }

        if (opt_mmap)
#endif
                chunk_dealloc_mmap(chunk, size);
}

/*
 * End chunk management functions.
 */
/******************************************************************************/
/*
 * Begin arena.
 */

/*
 * Choose an arena based on a per-thread value (fast-path code, calls slow-path
 * code if necessary).
 */
static inline arena_t *
choose_arena(void)
{
        arena_t *ret;

        /*
         * We can only use TLS if this is a PIC library, since for the static
         * library version, libc's malloc is used by TLS allocation, which
         * introduces a bootstrapping issue.
         */
#ifndef NO_TLS
        if (__isthreaded == false) {
            /* Avoid the overhead of TLS for single-threaded operation. */
            return (arenas[0]);
        }

        ret = arenas_map;
        if (ret == NULL) {
                ret = choose_arena_hard();
                assert(ret != NULL);
        }
#else
        if (__isthreaded && narenas > 1) {
                unsigned long ind;

                /*
                 * Hash _pthread_self() to one of the arenas.  There is a prime
                 * number of arenas, so this has a reasonable chance of
                 * working.  Even so, the hashing can be easily thwarted by
                 * inconvenient _pthread_self() values.  Without specific
                 * knowledge of how _pthread_self() calculates values, we can't
                 * easily do much better than this.
                 */
                ind = (unsigned long) _pthread_self() % narenas;

                /*
                 * Optimistially assume that arenas[ind] has been initialized.
                 * At worst, we find out that some other thread has already
                 * done so, after acquiring the lock in preparation.  Note that
                 * this lazy locking also has the effect of lazily forcing
                 * cache coherency; without the lock acquisition, there's no
                 * guarantee that modification of arenas[ind] by another thread
                 * would be seen on this CPU for an arbitrary amount of time.
                 *
                 * In general, this approach to modifying a synchronized value
                 * isn't a good idea, but in this case we only ever modify the
                 * value once, so things work out well.
                 */
                ret = arenas[ind];
                if (ret == NULL) {
                        /*
                         * Avoid races with another thread that may have already
                         * initialized arenas[ind].
                         */
                        malloc_spin_lock(&arenas_lock);
                        if (arenas[ind] == NULL)
                                ret = arenas_extend((unsigned)ind);
                        else
                                ret = arenas[ind];
                        malloc_spin_unlock(&arenas_lock);
                }
        } else
                ret = arenas[0];
#endif

        assert(ret != NULL);
        return (ret);
}

#ifndef NO_TLS
/*
 * Choose an arena based on a per-thread value (slow-path code only, called
 * only by choose_arena()).
 */
static arena_t *
choose_arena_hard(void)
{
        arena_t *ret;

        assert(__isthreaded);

#ifdef MALLOC_BALANCE
        /* Seed the PRNG used for arena load balancing. */
        SPRN(balance, (uint32_t)(uintptr_t)(_pthread_self()));
#endif

        if (narenas > 1) {
#ifdef MALLOC_BALANCE
                unsigned ind;

                ind = PRN(balance, narenas_2pow);
                if ((ret = arenas[ind]) == NULL) {
                        malloc_spin_lock(&arenas_lock);
                        if ((ret = arenas[ind]) == NULL)
                                ret = arenas_extend(ind);
                        malloc_spin_unlock(&arenas_lock);
                }
#else
                malloc_spin_lock(&arenas_lock);
                if ((ret = arenas[next_arena]) == NULL)
                        ret = arenas_extend(next_arena);
                next_arena = (next_arena + 1) % narenas;
                malloc_spin_unlock(&arenas_lock);
#endif
        } else
                ret = arenas[0];

        arenas_map = ret;

        return (ret);
}
#endif

static inline int
arena_chunk_comp(arena_chunk_t *a, arena_chunk_t *b)
{
        uintptr_t a_chunk = (uintptr_t)a;
        uintptr_t b_chunk = (uintptr_t)b;

        assert(a != NULL);
        assert(b != NULL);

        return ((a_chunk > b_chunk) - (a_chunk < b_chunk));
}

/* Wrap red-black tree macros in functions. */
rb_wrap(__unused static, arena_chunk_tree_dirty_, arena_chunk_tree_t,
    arena_chunk_t, link_dirty, arena_chunk_comp)

static inline int
arena_run_comp(arena_chunk_map_t *a, arena_chunk_map_t *b)
{
        uintptr_t a_mapelm = (uintptr_t)a;
        uintptr_t b_mapelm = (uintptr_t)b;

        assert(a != NULL);
        assert(b != NULL);

        return ((a_mapelm > b_mapelm) - (a_mapelm < b_mapelm));
}

/* Wrap red-black tree macros in functions. */
rb_wrap(__unused static, arena_run_tree_, arena_run_tree_t, arena_chunk_map_t,
    link, arena_run_comp)

static inline int
arena_avail_comp(arena_chunk_map_t *a, arena_chunk_map_t *b)
{
        int ret;
        size_t a_size = a->bits & ~pagesize_mask;
        size_t b_size = b->bits & ~pagesize_mask;

        ret = (a_size > b_size) - (a_size < b_size);
        if (ret == 0) {
                uintptr_t a_mapelm, b_mapelm;

                if ((a->bits & CHUNK_MAP_KEY) == 0)
                        a_mapelm = (uintptr_t)a;
                else {
                        /*
                         * Treat keys as though they are lower than anything
                         * else.
                         */
                        a_mapelm = 0;
                }
                b_mapelm = (uintptr_t)b;

                ret = (a_mapelm > b_mapelm) - (a_mapelm < b_mapelm);
        }

        return (ret);
}

/* Wrap red-black tree macros in functions. */
rb_wrap(__unused static, arena_avail_tree_, arena_avail_tree_t,
    arena_chunk_map_t, link, arena_avail_comp)

static inline void *
arena_run_reg_alloc(arena_run_t *run, arena_bin_t *bin)
{
        void *ret;
        unsigned i, mask, bit, regind;

        assert(run->magic == ARENA_RUN_MAGIC);
        assert(run->regs_minelm < bin->regs_mask_nelms);

        /*
         * Move the first check outside the loop, so that run->regs_minelm can
         * be updated unconditionally, without the possibility of updating it
         * multiple times.
         */
        i = run->regs_minelm;
        mask = run->regs_mask[i];
        if (mask != 0) {
                /* Usable allocation found. */
                bit = ffs((int)mask) - 1;

                regind = ((i << (SIZEOF_INT_2POW + 3)) + bit);
                assert(regind < bin->nregs);
                ret = (void *)(((uintptr_t)run) + bin->reg0_offset
                    + (bin->reg_size * regind));

                /* Clear bit. */
                mask ^= (1U << bit);
                run->regs_mask[i] = mask;

                return (ret);
        }

        for (i++; i < bin->regs_mask_nelms; i++) {
                mask = run->regs_mask[i];
                if (mask != 0) {
                        /* Usable allocation found. */
                        bit = ffs((int)mask) - 1;

                        regind = ((i << (SIZEOF_INT_2POW + 3)) + bit);
                        assert(regind < bin->nregs);
                        ret = (void *)(((uintptr_t)run) + bin->reg0_offset
                            + (bin->reg_size * regind));

                        /* Clear bit. */
                        mask ^= (1U << bit);
                        run->regs_mask[i] = mask;

                        /*
                         * Make a note that nothing before this element
                         * contains a free region.
                         */
                        run->regs_minelm = i; /* Low payoff: + (mask == 0); */

                        return (ret);
                }
        }
        /* Not reached. */
        assert(0);
        return (NULL);
}

static inline void
arena_run_reg_dalloc(arena_run_t *run, arena_bin_t *bin, void *ptr, size_t size)
{
        /*
         * To divide by a number D that is not a power of two we multiply
         * by (2^21 / D) and then right shift by 21 positions.
         *
         *   X / D
         *
         * becomes
         *
         *   (X * size_invs[(D >> QUANTUM_2POW_MIN) - 3]) >> SIZE_INV_SHIFT
         */
#define SIZE_INV_SHIFT 21
#define SIZE_INV(s) (((1U << SIZE_INV_SHIFT) / (s << QUANTUM_2POW_MIN)) + 1)
        static const unsigned size_invs[] = {
            SIZE_INV(3),
            SIZE_INV(4), SIZE_INV(5), SIZE_INV(6), SIZE_INV(7),
            SIZE_INV(8), SIZE_INV(9), SIZE_INV(10), SIZE_INV(11),
            SIZE_INV(12),SIZE_INV(13), SIZE_INV(14), SIZE_INV(15),
            SIZE_INV(16),SIZE_INV(17), SIZE_INV(18), SIZE_INV(19),
            SIZE_INV(20),SIZE_INV(21), SIZE_INV(22), SIZE_INV(23),
            SIZE_INV(24),SIZE_INV(25), SIZE_INV(26), SIZE_INV(27),
            SIZE_INV(28),SIZE_INV(29), SIZE_INV(30), SIZE_INV(31)
#if (QUANTUM_2POW_MIN < 4)
            ,
            SIZE_INV(32), SIZE_INV(33), SIZE_INV(34), SIZE_INV(35),
            SIZE_INV(36), SIZE_INV(37), SIZE_INV(38), SIZE_INV(39),
            SIZE_INV(40), SIZE_INV(41), SIZE_INV(42), SIZE_INV(43),
            SIZE_INV(44), SIZE_INV(45), SIZE_INV(46), SIZE_INV(47),
            SIZE_INV(48), SIZE_INV(49), SIZE_INV(50), SIZE_INV(51),
            SIZE_INV(52), SIZE_INV(53), SIZE_INV(54), SIZE_INV(55),
            SIZE_INV(56), SIZE_INV(57), SIZE_INV(58), SIZE_INV(59),
            SIZE_INV(60), SIZE_INV(61), SIZE_INV(62), SIZE_INV(63)
#endif
        };
        unsigned diff, regind, elm, bit;

        assert(run->magic == ARENA_RUN_MAGIC);
        assert(((sizeof(size_invs)) / sizeof(unsigned)) + 3
            >= (SMALL_MAX_DEFAULT >> QUANTUM_2POW_MIN));

        /*
         * Avoid doing division with a variable divisor if possible.  Using
         * actual division here can reduce allocator throughput by over 20%!
         */
        diff = (unsigned)((uintptr_t)ptr - (uintptr_t)run - bin->reg0_offset);
        if ((size & (size - 1)) == 0) {
                /*
                 * log2_table allows fast division of a power of two in the
                 * [1..128] range.
                 *
                 * (x / divisor) becomes (x >> log2_table[divisor - 1]).
                 */
                static const unsigned char log2_table[] = {
                    0, 1, 0, 2, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 4,
                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 5,
                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 6,
                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7
                };

                if (size <= 128)
                        regind = (diff >> log2_table[size - 1]);
                else if (size <= 32768)
                        regind = diff >> (8 + log2_table[(size >> 8) - 1]);
                else {
                        /*
                         * The run size is too large for us to use the lookup
                         * table.  Use real division.
                         */
                        regind = diff / size;
                }
        } else if (size <= (((sizeof(size_invs) / sizeof(unsigned)) + 2)
            << QUANTUM_2POW_MIN)) {
                regind = size_invs[(size >> QUANTUM_2POW_MIN) - 3] * diff;
                regind >>= SIZE_INV_SHIFT;
        } else {
                /*
                 * size_invs isn't large enough to handle this size class, so
                 * calculate regind using actual division.  This only happens
                 * if the user increases small_max via the 'S' runtime
                 * configuration option.
                 */
                regind = diff / size;
        };
        assert(diff == regind * size);
        assert(regind < bin->nregs);

        elm = regind >> (SIZEOF_INT_2POW + 3);
        if (elm < run->regs_minelm)
                run->regs_minelm = elm;
        bit = regind - (elm << (SIZEOF_INT_2POW + 3));
        assert((run->regs_mask[elm] & (1U << bit)) == 0);
        run->regs_mask[elm] |= (1U << bit);
#undef SIZE_INV
#undef SIZE_INV_SHIFT
}

static void
arena_run_split(arena_t *arena, arena_run_t *run, size_t size, bool large,
    bool zero)
{
        arena_chunk_t *chunk;
        size_t old_ndirty, run_ind, total_pages, need_pages, rem_pages, i;

        chunk = (arena_chunk_t *)CHUNK_ADDR2BASE(run);
        old_ndirty = chunk->ndirty;
        run_ind = (unsigned)(((uintptr_t)run - (uintptr_t)chunk)
            >> pagesize_2pow);
        total_pages = (chunk->map[run_ind].bits & ~pagesize_mask) >>
            pagesize_2pow;
        need_pages = (size >> pagesize_2pow);
        assert(need_pages > 0);
        assert(need_pages <= total_pages);
        rem_pages = total_pages - need_pages;

        arena_avail_tree_remove(&arena->runs_avail, &chunk->map[run_ind]);

        /* Keep track of trailing unused pages for later use. */
        if (rem_pages > 0) {
                chunk->map[run_ind+need_pages].bits = (rem_pages <<
                    pagesize_2pow) | (chunk->map[run_ind+need_pages].bits &
                    pagesize_mask);
                chunk->map[run_ind+total_pages-1].bits = (rem_pages <<
                    pagesize_2pow) | (chunk->map[run_ind+total_pages-1].bits &
                    pagesize_mask);
                arena_avail_tree_insert(&arena->runs_avail,
                    &chunk->map[run_ind+need_pages]);
        }

        for (i = 0; i < need_pages; i++) {
                /* Zero if necessary. */
                if (zero) {
                        if ((chunk->map[run_ind + i].bits & CHUNK_MAP_ZEROED)
                            == 0) {
                                memset((void *)((uintptr_t)chunk + ((run_ind
                                    + i) << pagesize_2pow)), 0, pagesize);
                                /* CHUNK_MAP_ZEROED is cleared below. */
                        }
                }

                /* Update dirty page accounting. */
                if (chunk->map[run_ind + i].bits & CHUNK_MAP_DIRTY) {
                        chunk->ndirty--;
                        arena->ndirty--;
                        /* CHUNK_MAP_DIRTY is cleared below. */
                }

                /* Initialize the chunk map. */
                if (large) {
                        chunk->map[run_ind + i].bits = CHUNK_MAP_LARGE
                            | CHUNK_MAP_ALLOCATED;
                } else {
                        chunk->map[run_ind + i].bits = (size_t)run
                            | CHUNK_MAP_ALLOCATED;
                }
        }

        /*
         * Set the run size only in the first element for large runs.  This is
         * primarily a debugging aid, since the lack of size info for trailing
         * pages only matters if the application tries to operate on an
         * interior pointer.
         */
        if (large)
                chunk->map[run_ind].bits |= size;

        if (chunk->ndirty == 0 && old_ndirty > 0)
                arena_chunk_tree_dirty_remove(&arena->chunks_dirty, chunk);
}

static arena_chunk_t *
arena_chunk_alloc(arena_t *arena)
{
        arena_chunk_t *chunk;
        size_t i;

        if (arena->spare != NULL) {
                chunk = arena->spare;
                arena->spare = NULL;
        } else {
                chunk = (arena_chunk_t *)chunk_alloc(chunksize, true);
                if (chunk == NULL)
                        return (NULL);
#ifdef MALLOC_STATS
                arena->stats.mapped += chunksize;
#endif

                chunk->arena = arena;

                /*
                 * Claim that no pages are in use, since the header is merely
                 * overhead.
                 */
                chunk->ndirty = 0;

                /*
                 * Initialize the map to contain one maximal free untouched run.
                 */
                for (i = 0; i < arena_chunk_header_npages; i++)
                        chunk->map[i].bits = 0;
                chunk->map[i].bits = arena_maxclass | CHUNK_MAP_ZEROED;
                for (i++; i < chunk_npages-1; i++) {
                        chunk->map[i].bits = CHUNK_MAP_ZEROED;
                }
                chunk->map[chunk_npages-1].bits = arena_maxclass |
                    CHUNK_MAP_ZEROED;
        }

        /* Insert the run into the runs_avail tree. */
        arena_avail_tree_insert(&arena->runs_avail,
            &chunk->map[arena_chunk_header_npages]);

        return (chunk);
}

static void
arena_chunk_dealloc(arena_t *arena, arena_chunk_t *chunk)
{

        if (arena->spare != NULL) {
                if (arena->spare->ndirty > 0) {
                        arena_chunk_tree_dirty_remove(
                            &chunk->arena->chunks_dirty, arena->spare);
                        arena->ndirty -= arena->spare->ndirty;
                }
                chunk_dealloc((void *)arena->spare, chunksize);
#ifdef MALLOC_STATS
                arena->stats.mapped -= chunksize;
#endif
        }

        /*
         * Remove run from runs_avail, regardless of whether this chunk
         * will be cached, so that the arena does not use it.  Dirty page
         * flushing only uses the chunks_dirty tree, so leaving this chunk in
         * the chunks_* trees is sufficient for that purpose.
         */
        arena_avail_tree_remove(&arena->runs_avail,
            &chunk->map[arena_chunk_header_npages]);

        arena->spare = chunk;
}

static arena_run_t *
arena_run_alloc(arena_t *arena, size_t size, bool large, bool zero)
{
        arena_chunk_t *chunk;
        arena_run_t *run;
        arena_chunk_map_t *mapelm, key;

        assert(size <= arena_maxclass);
        assert((size & pagesize_mask) == 0);

        /* Search the arena's chunks for the lowest best fit. */
        key.bits = size | CHUNK_MAP_KEY;
        mapelm = arena_avail_tree_nsearch(&arena->runs_avail, &key);
        if (mapelm != NULL) {
                arena_chunk_t *run_chunk = CHUNK_ADDR2BASE(mapelm);
                size_t pageind = ((uintptr_t)mapelm - (uintptr_t)run_chunk->map)
                    / sizeof(arena_chunk_map_t);

                run = (arena_run_t *)((uintptr_t)run_chunk + (pageind
                    << pagesize_2pow));
                arena_run_split(arena, run, size, large, zero);
                return (run);
        }

        /*
         * No usable runs.  Create a new chunk from which to allocate the run.
         */
        chunk = arena_chunk_alloc(arena);
        if (chunk == NULL)
                return (NULL);
        run = (arena_run_t *)((uintptr_t)chunk + (arena_chunk_header_npages <<
            pagesize_2pow));
        /* Update page map. */
        arena_run_split(arena, run, size, large, zero);
        return (run);
}

static void
arena_purge(arena_t *arena)
{
        arena_chunk_t *chunk;
        size_t i, npages;
#ifdef MALLOC_DEBUG
        size_t ndirty = 0;

        rb_foreach_begin(arena_chunk_t, link_dirty, &arena->chunks_dirty,
            chunk) {
                ndirty += chunk->ndirty;
        } rb_foreach_end(arena_chunk_t, link_dirty, &arena->chunks_dirty, chunk)
        assert(ndirty == arena->ndirty);
#endif
        assert(arena->ndirty > opt_dirty_max);

#ifdef MALLOC_STATS
        arena->stats.npurge++;
#endif

        /*
         * Iterate downward through chunks until enough dirty memory has been
         * purged.  Terminate as soon as possible in order to minimize the
         * number of system calls, even if a chunk has only been partially
         * purged.
         */
        while (arena->ndirty > (opt_dirty_max >> 1)) {
                chunk = arena_chunk_tree_dirty_last(&arena->chunks_dirty);
                assert(chunk != NULL);

                for (i = chunk_npages - 1; chunk->ndirty > 0; i--) {
                        assert(i >= arena_chunk_header_npages);

                        if (chunk->map[i].bits & CHUNK_MAP_DIRTY) {
                                chunk->map[i].bits ^= CHUNK_MAP_DIRTY;
                                /* Find adjacent dirty run(s). */
                                for (npages = 1; i > arena_chunk_header_npages
                                    && (chunk->map[i - 1].bits &
                                    CHUNK_MAP_DIRTY); npages++) {
                                        i--;
                                        chunk->map[i].bits ^= CHUNK_MAP_DIRTY;
                                }
                                chunk->ndirty -= npages;
                                arena->ndirty -= npages;

                                madvise((void *)((uintptr_t)chunk + (i <<
                                    pagesize_2pow)), (npages << pagesize_2pow),
                                    MADV_FREE);
#ifdef MALLOC_STATS
                                arena->stats.nmadvise++;
                                arena->stats.purged += npages;
#endif
                                if (arena->ndirty <= (opt_dirty_max >> 1))
                                        break;
                        }
                }

                if (chunk->ndirty == 0) {
                        arena_chunk_tree_dirty_remove(&arena->chunks_dirty,
                            chunk);
                }
        }
}

static void
arena_run_dalloc(arena_t *arena, arena_run_t *run, bool dirty)
{
        arena_chunk_t *chunk;
        size_t size, run_ind, run_pages;

        chunk = (arena_chunk_t *)CHUNK_ADDR2BASE(run);
        run_ind = (size_t)(((uintptr_t)run - (uintptr_t)chunk)
            >> pagesize_2pow);
        assert(run_ind >= arena_chunk_header_npages);
        assert(run_ind < chunk_npages);
        if ((chunk->map[run_ind].bits & CHUNK_MAP_LARGE) != 0)
                size = chunk->map[run_ind].bits & ~pagesize_mask;
        else
                size = run->bin->run_size;
        run_pages = (size >> pagesize_2pow);

        /* Mark pages as unallocated in the chunk map. */
        if (dirty) {
                size_t i;

                for (i = 0; i < run_pages; i++) {
                        assert((chunk->map[run_ind + i].bits & CHUNK_MAP_DIRTY)
                            == 0);
                        chunk->map[run_ind + i].bits = CHUNK_MAP_DIRTY;
                }

                if (chunk->ndirty == 0) {
                        arena_chunk_tree_dirty_insert(&arena->chunks_dirty,
                            chunk);
                }
                chunk->ndirty += run_pages;
                arena->ndirty += run_pages;
        } else {
                size_t i;

                for (i = 0; i < run_pages; i++) {
                        chunk->map[run_ind + i].bits &= ~(CHUNK_MAP_LARGE |
                            CHUNK_MAP_ALLOCATED);
                }
        }
        chunk->map[run_ind].bits = size | (chunk->map[run_ind].bits &
            pagesize_mask);
        chunk->map[run_ind+run_pages-1].bits = size |
            (chunk->map[run_ind+run_pages-1].bits & pagesize_mask);

        /* Try to coalesce forward. */
        if (run_ind + run_pages < chunk_npages &&
            (chunk->map[run_ind+run_pages].bits & CHUNK_MAP_ALLOCATED) == 0) {
                size_t nrun_size = chunk->map[run_ind+run_pages].bits &
                    ~pagesize_mask;

                /*
                 * Remove successor from runs_avail; the coalesced run is
                 * inserted later.
                 */
                arena_avail_tree_remove(&arena->runs_avail,
                    &chunk->map[run_ind+run_pages]);

                size += nrun_size;
                run_pages = size >> pagesize_2pow;

                assert((chunk->map[run_ind+run_pages-1].bits & ~pagesize_mask)
                    == nrun_size);
                chunk->map[run_ind].bits = size | (chunk->map[run_ind].bits &
                    pagesize_mask);
                chunk->map[run_ind+run_pages-1].bits = size |
                    (chunk->map[run_ind+run_pages-1].bits & pagesize_mask);
        }

        /* Try to coalesce backward. */
        if (run_ind > arena_chunk_header_npages && (chunk->map[run_ind-1].bits &
            CHUNK_MAP_ALLOCATED) == 0) {
                size_t prun_size = chunk->map[run_ind-1].bits & ~pagesize_mask;

                run_ind -= prun_size >> pagesize_2pow;

                /*
                 * Remove predecessor from runs_avail; the coalesced run is
                 * inserted later.
                 */
                arena_avail_tree_remove(&arena->runs_avail,
                    &chunk->map[run_ind]);

                size += prun_size;
                run_pages = size >> pagesize_2pow;

                assert((chunk->map[run_ind].bits & ~pagesize_mask) ==
                    prun_size);
                chunk->map[run_ind].bits = size | (chunk->map[run_ind].bits &
                    pagesize_mask);
                chunk->map[run_ind+run_pages-1].bits = size |
                    (chunk->map[run_ind+run_pages-1].bits & pagesize_mask);
        }

        /* Insert into runs_avail, now that coalescing is complete. */
        arena_avail_tree_insert(&arena->runs_avail, &chunk->map[run_ind]);

        /* Deallocate chunk if it is now completely unused. */
        if ((chunk->map[arena_chunk_header_npages].bits & (~pagesize_mask |
            CHUNK_MAP_ALLOCATED)) == arena_maxclass)
                arena_chunk_dealloc(arena, chunk);

        /* Enforce opt_dirty_max. */
        if (arena->ndirty > opt_dirty_max)
                arena_purge(arena);
}

static void
arena_run_trim_head(arena_t *arena, arena_chunk_t *chunk, arena_run_t *run,
    size_t oldsize, size_t newsize)
{
        size_t pageind = ((uintptr_t)run - (uintptr_t)chunk) >> pagesize_2pow;
        size_t head_npages = (oldsize - newsize) >> pagesize_2pow;

        assert(oldsize > newsize);

        /*
         * Update the chunk map so that arena_run_dalloc() can treat the
         * leading run as separately allocated.
         */
        chunk->map[pageind].bits = (oldsize - newsize) | CHUNK_MAP_LARGE |
            CHUNK_MAP_ALLOCATED;
        chunk->map[pageind+head_npages].bits = newsize | CHUNK_MAP_LARGE |
            CHUNK_MAP_ALLOCATED;

        arena_run_dalloc(arena, run, false);
}

static void
arena_run_trim_tail(arena_t *arena, arena_chunk_t *chunk, arena_run_t *run,
    size_t oldsize, size_t newsize, bool dirty)
{
        size_t pageind = ((uintptr_t)run - (uintptr_t)chunk) >> pagesize_2pow;
        size_t npages = newsize >> pagesize_2pow;

        assert(oldsize > newsize);

        /*
         * Update the chunk map so that arena_run_dalloc() can treat the
         * trailing run as separately allocated.
         */
        chunk->map[pageind].bits = newsize | CHUNK_MAP_LARGE |
            CHUNK_MAP_ALLOCATED;
        chunk->map[pageind+npages].bits = (oldsize - newsize) | CHUNK_MAP_LARGE
            | CHUNK_MAP_ALLOCATED;

        arena_run_dalloc(arena, (arena_run_t *)((uintptr_t)run + newsize),
            dirty);
}

static arena_run_t *
arena_bin_nonfull_run_get(arena_t *arena, arena_bin_t *bin)
{
        arena_chunk_map_t *mapelm;
        arena_run_t *run;
        unsigned i, remainder;

        /* Look for a usable run. */
        mapelm = arena_run_tree_first(&bin->runs);
        if (mapelm != NULL) {
                /* run is guaranteed to have available space. */
                arena_run_tree_remove(&bin->runs, mapelm);
                run = (arena_run_t *)(mapelm->bits & ~pagesize_mask);
#ifdef MALLOC_STATS
                bin->stats.reruns++;
#endif
                return (run);
        }
        /* No existing runs have any space available. */

        /* Allocate a new run. */
        run = arena_run_alloc(arena, bin->run_size, false, false);
        if (run == NULL)
                return (NULL);

        /* Initialize run internals. */
        run->bin = bin;

        for (i = 0; i < bin->regs_mask_nelms - 1; i++)
                run->regs_mask[i] = UINT_MAX;
        remainder = bin->nregs & ((1U << (SIZEOF_INT_2POW + 3)) - 1);
        if (remainder == 0)
                run->regs_mask[i] = UINT_MAX;
        else {
                /* The last element has spare bits that need to be unset. */
                run->regs_mask[i] = (UINT_MAX >> ((1U << (SIZEOF_INT_2POW + 3))
                    - remainder));
        }

        run->regs_minelm = 0;

        run->nfree = bin->nregs;
#ifdef MALLOC_DEBUG
        run->magic = ARENA_RUN_MAGIC;
#endif

#ifdef MALLOC_STATS
        bin->stats.nruns++;
        bin->stats.curruns++;
        if (bin->stats.curruns > bin->stats.highruns)
                bin->stats.highruns = bin->stats.curruns;
#endif
        return (run);
}

/* bin->runcur must have space available before this function is called. */
static inline void *
arena_bin_malloc_easy(arena_t *arena, arena_bin_t *bin, arena_run_t *run)
{
        void *ret;

        assert(run->magic == ARENA_RUN_MAGIC);
        assert(run->nfree > 0);

        ret = arena_run_reg_alloc(run, bin);
        assert(ret != NULL);
        run->nfree--;

        return (ret);
}

/* Re-fill bin->runcur, then call arena_bin_malloc_easy(). */
static void *
arena_bin_malloc_hard(arena_t *arena, arena_bin_t *bin)
{

        bin->runcur = arena_bin_nonfull_run_get(arena, bin);
        if (bin->runcur == NULL)
                return (NULL);
        assert(bin->runcur->magic == ARENA_RUN_MAGIC);
        assert(bin->runcur->nfree > 0);

        return (arena_bin_malloc_easy(arena, bin, bin->runcur));
}

/*
 * Calculate bin->run_size such that it meets the following constraints:
 *
 *   *) bin->run_size >= min_run_size
 *   *) bin->run_size <= arena_maxclass
 *   *) bin->run_size <= RUN_MAX_SMALL
 *   *) run header overhead <= RUN_MAX_OVRHD (or header overhead relaxed).
 *
 * bin->nregs, bin->regs_mask_nelms, and bin->reg0_offset are
 * also calculated here, since these settings are all interdependent.
 */
static size_t
arena_bin_run_size_calc(arena_bin_t *bin, size_t min_run_size)
{
        size_t try_run_size, good_run_size;
        unsigned good_nregs, good_mask_nelms, good_reg0_offset;
        unsigned try_nregs, try_mask_nelms, try_reg0_offset;

        assert(min_run_size >= pagesize);
        assert(min_run_size <= arena_maxclass);
        assert(min_run_size <= RUN_MAX_SMALL);

        /*
         * Calculate known-valid settings before entering the run_size
         * expansion loop, so that the first part of the loop always copies
         * valid settings.
         *
         * The do..while loop iteratively reduces the number of regions until
         * the run header and the regions no longer overlap.  A closed formula
         * would be quite messy, since there is an interdependency between the
         * header's mask length and the number of regions.
         */
        try_run_size = min_run_size;
        try_nregs = ((try_run_size - sizeof(arena_run_t)) / bin->reg_size)
            + 1; /* Counter-act try_nregs-- in loop. */
        do {
                try_nregs--;
                try_mask_nelms = (try_nregs >> (SIZEOF_INT_2POW + 3)) +
                    ((try_nregs & ((1U << (SIZEOF_INT_2POW + 3)) - 1)) ? 1 : 0);
                try_reg0_offset = try_run_size - (try_nregs * bin->reg_size);
        } while (sizeof(arena_run_t) + (sizeof(unsigned) * (try_mask_nelms - 1))
            > try_reg0_offset);

        /* run_size expansion loop. */
        do {
                /*
                 * Copy valid settings before trying more aggressive settings.
                 */
                good_run_size = try_run_size;
                good_nregs = try_nregs;
                good_mask_nelms = try_mask_nelms;
                good_reg0_offset = try_reg0_offset;

                /* Try more aggressive settings. */
                try_run_size += pagesize;
                try_nregs = ((try_run_size - sizeof(arena_run_t)) /
                    bin->reg_size) + 1; /* Counter-act try_nregs-- in loop. */
                do {
                        try_nregs--;
                        try_mask_nelms = (try_nregs >> (SIZEOF_INT_2POW + 3)) +
                            ((try_nregs & ((1U << (SIZEOF_INT_2POW + 3)) - 1)) ?
                            1 : 0);
                        try_reg0_offset = try_run_size - (try_nregs *
                            bin->reg_size);
                } while (sizeof(arena_run_t) + (sizeof(unsigned) *
                    (try_mask_nelms - 1)) > try_reg0_offset);
        } while (try_run_size <= arena_maxclass && try_run_size <= RUN_MAX_SMALL
            && RUN_MAX_OVRHD * (bin->reg_size << 3) > RUN_MAX_OVRHD_RELAX
            && (try_reg0_offset << RUN_BFP) > RUN_MAX_OVRHD * try_run_size);

        assert(sizeof(arena_run_t) + (sizeof(unsigned) * (good_mask_nelms - 1))
            <= good_reg0_offset);
        assert((good_mask_nelms << (SIZEOF_INT_2POW + 3)) >= good_nregs);

        /* Copy final settings. */
        bin->run_size = good_run_size;
        bin->nregs = good_nregs;
        bin->regs_mask_nelms = good_mask_nelms;
        bin->reg0_offset = good_reg0_offset;

        return (good_run_size);
}

#ifdef MALLOC_BALANCE
static inline void
arena_lock_balance(arena_t *arena)
{
        unsigned contention;

        contention = malloc_spin_lock(&arena->lock);
        if (narenas > 1) {
                /*
                 * Calculate the exponentially averaged contention for this
                 * arena.  Due to integer math always rounding down, this value
                 * decays somewhat faster then normal.
                 */
                arena->contention = (((uint64_t)arena->contention
                    * (uint64_t)((1U << BALANCE_ALPHA_INV_2POW)-1))
                    + (uint64_t)contention) >> BALANCE_ALPHA_INV_2POW;
                if (arena->contention >= opt_balance_threshold)
                        arena_lock_balance_hard(arena);
        }
}

static void
arena_lock_balance_hard(arena_t *arena)
{
        uint32_t ind;

        arena->contention = 0;
#ifdef MALLOC_STATS
        arena->stats.nbalance++;
#endif
        ind = PRN(balance, narenas_2pow);
        if (arenas[ind] != NULL)
                arenas_map = arenas[ind];
        else {
                malloc_spin_lock(&arenas_lock);
                if (arenas[ind] != NULL)
                        arenas_map = arenas[ind];
                else
                        arenas_map = arenas_extend(ind);
                malloc_spin_unlock(&arenas_lock);
        }
}
#endif

static inline void *
arena_malloc_small(arena_t *arena, size_t size, bool zero)
{
        void *ret;
        arena_bin_t *bin;
        arena_run_t *run;

        if (size < small_min) {
                /* Tiny. */
                size = pow2_ceil(size);
                bin = &arena->bins[ffs((int)(size >> (TINY_MIN_2POW +
                    1)))];
#if (!defined(NDEBUG) || defined(MALLOC_STATS))
                /*
                 * Bin calculation is always correct, but we may need
                 * to fix size for the purposes of assertions and/or
                 * stats accuracy.
                 */
                if (size < (1U << TINY_MIN_2POW))
                        size = (1U << TINY_MIN_2POW);
#endif
        } else if (size <= small_max) {
                /* Quantum-spaced. */
                size = QUANTUM_CEILING(size);
                bin = &arena->bins[ntbins + (size >> opt_quantum_2pow)
                    - 1];
        } else {
                /* Sub-page. */
                size = pow2_ceil(size);
                bin = &arena->bins[ntbins + nqbins
                    + (ffs((int)(size >> opt_small_max_2pow)) - 2)];
        }
        assert(size == bin->reg_size);

#ifdef MALLOC_BALANCE
        arena_lock_balance(arena);
#else
        malloc_spin_lock(&arena->lock);
#endif
        if ((run = bin->runcur) != NULL && run->nfree > 0)
                ret = arena_bin_malloc_easy(arena, bin, run);
        else
                ret = arena_bin_malloc_hard(arena, bin);

        if (ret == NULL) {
                malloc_spin_unlock(&arena->lock);
                return (NULL);
        }

#ifdef MALLOC_STATS
        bin->stats.nrequests++;
        arena->stats.nmalloc_small++;
        arena->stats.allocated_small += size;
#endif
        malloc_spin_unlock(&arena->lock);

        if (zero == false) {
                if (opt_junk)
                        memset(ret, 0xa5, size);
                else if (opt_zero)
                        memset(ret, 0, size);
        } else
                memset(ret, 0, size);

        return (ret);
}

static void *
arena_malloc_large(arena_t *arena, size_t size, bool zero)
{
        void *ret;

        /* Large allocation. */
        size = PAGE_CEILING(size);
#ifdef MALLOC_BALANCE
        arena_lock_balance(arena);
#else
        malloc_spin_lock(&arena->lock);
#endif
        ret = (void *)arena_run_alloc(arena, size, true, zero);
        if (ret == NULL) {
                malloc_spin_unlock(&arena->lock);
                return (NULL);
        }
#ifdef MALLOC_STATS
        arena->stats.nmalloc_large++;
        arena->stats.allocated_large += size;
#endif
        malloc_spin_unlock(&arena->lock);

        if (zero == false) {
                if (opt_junk)
                        memset(ret, 0xa5, size);
                else if (opt_zero)
                        memset(ret, 0, size);
        }

        return (ret);
}

static inline void *
arena_malloc(arena_t *arena, size_t size, bool zero)
{

        assert(arena != NULL);
        assert(arena->magic == ARENA_MAGIC);
        assert(size != 0);
        assert(QUANTUM_CEILING(size) <= arena_maxclass);

        if (size <= bin_maxclass) {
                return (arena_malloc_small(arena, size, zero));
        } else
                return (arena_malloc_large(arena, size, zero));
}

static inline void *
imalloc(size_t size)
{

        assert(size != 0);

        if (size <= arena_maxclass)
                return (arena_malloc(choose_arena(), size, false));
        else
                return (huge_malloc(size, false));
}

static inline void *
icalloc(size_t size)
{

        if (size <= arena_maxclass)
                return (arena_malloc(choose_arena(), size, true));
        else
                return (huge_malloc(size, true));
}

/* Only handles large allocations that require more than page alignment. */
static void *
arena_palloc(arena_t *arena, size_t alignment, size_t size, size_t alloc_size)
{
        void *ret;
        size_t offset;
        arena_chunk_t *chunk;

        assert((size & pagesize_mask) == 0);
        assert((alignment & pagesize_mask) == 0);

#ifdef MALLOC_BALANCE
        arena_lock_balance(arena);
#else
        malloc_spin_lock(&arena->lock);
#endif
        ret = (void *)arena_run_alloc(arena, alloc_size, true, false);
        if (ret == NULL) {
                malloc_spin_unlock(&arena->lock);
                return (NULL);
        }

        chunk = (arena_chunk_t *)CHUNK_ADDR2BASE(ret);

        offset = (uintptr_t)ret & (alignment - 1);
        assert((offset & pagesize_mask) == 0);
        assert(offset < alloc_size);
        if (offset == 0)
                arena_run_trim_tail(arena, chunk, ret, alloc_size, size, false);
        else {
                size_t leadsize, trailsize;

                leadsize = alignment - offset;
                if (leadsize > 0) {
                        arena_run_trim_head(arena, chunk, ret, alloc_size,
                            alloc_size - leadsize);
                        ret = (void *)((uintptr_t)ret + leadsize);
                }

                trailsize = alloc_size - leadsize - size;
                if (trailsize != 0) {
                        /* Trim trailing space. */
                        assert(trailsize < alloc_size);
                        arena_run_trim_tail(arena, chunk, ret, size + trailsize,
                            size, false);
                }
        }

#ifdef MALLOC_STATS
        arena->stats.nmalloc_large++;
        arena->stats.allocated_large += size;
#endif
        malloc_spin_unlock(&arena->lock);

        if (opt_junk)
                memset(ret, 0xa5, size);
        else if (opt_zero)
                memset(ret, 0, size);
        return (ret);
}

static inline void *
ipalloc(size_t alignment, size_t size)
{
        void *ret;
        size_t ceil_size;

        /*
         * Round size up to the nearest multiple of alignment.
         *
         * This done, we can take advantage of the fact that for each small
         * size class, every object is aligned at the smallest power of two
         * that is non-zero in the base two representation of the size.  For
         * example:
         *
         *   Size |   Base 2 | Minimum alignment
         *   -----+----------+------------------
         *     96 |  1100000 |  32
         *    144 | 10100000 |  32
         *    192 | 11000000 |  64
         *
         * Depending on runtime settings, it is possible that arena_malloc()
         * will further round up to a power of two, but that never causes
         * correctness issues.
         */
        ceil_size = (size + (alignment - 1)) & (-alignment);
        /*
         * (ceil_size < size) protects against the combination of maximal
         * alignment and size greater than maximal alignment.
         */
        if (ceil_size < size) {
                /* size_t overflow. */
                return (NULL);
        }

        if (ceil_size <= pagesize || (alignment <= pagesize
            && ceil_size <= arena_maxclass))
                ret = arena_malloc(choose_arena(), ceil_size, false);
        else {
                size_t run_size;

                /*
                 * We can't achieve sub-page alignment, so round up alignment
                 * permanently; it makes later calculations simpler.
                 */
                alignment = PAGE_CEILING(alignment);
                ceil_size = PAGE_CEILING(size);
                /*
                 * (ceil_size < size) protects against very large sizes within
                 * pagesize of SIZE_T_MAX.
                 *
                 * (ceil_size + alignment < ceil_size) protects against the
                 * combination of maximal alignment and ceil_size large enough
                 * to cause overflow.  This is similar to the first overflow
                 * check above, but it needs to be repeated due to the new
                 * ceil_size value, which may now be *equal* to maximal
                 * alignment, whereas before we only detected overflow if the
                 * original size was *greater* than maximal alignment.
                 */
                if (ceil_size < size || ceil_size + alignment < ceil_size) {
                        /* size_t overflow. */
                        return (NULL);
                }

                /*
                 * Calculate the size of the over-size run that arena_palloc()
                 * would need to allocate in order to guarantee the alignment.
                 */
                if (ceil_size >= alignment)
                        run_size = ceil_size + alignment - pagesize;
                else {
                        /*
                         * It is possible that (alignment << 1) will cause
                         * overflow, but it doesn't matter because we also
                         * subtract pagesize, which in the case of overflow
                         * leaves us with a very large run_size.  That causes
                         * the first conditional below to fail, which means
                         * that the bogus run_size value never gets used for
                         * anything important.
                         */
                        run_size = (alignment << 1) - pagesize;
                }

                if (run_size <= arena_maxclass) {
                        ret = arena_palloc(choose_arena(), alignment, ceil_size,
                            run_size);
                } else if (alignment <= chunksize)
                        ret = huge_malloc(ceil_size, false);
                else
                        ret = huge_palloc(alignment, ceil_size);
        }

        assert(((uintptr_t)ret & (alignment - 1)) == 0);
        return (ret);
}

/* Return the size of the allocation pointed to by ptr. */
static size_t
arena_salloc(const void *ptr)
{
        size_t ret;
        arena_chunk_t *chunk;
        size_t pageind, mapbits;

        assert(ptr != NULL);
        assert(CHUNK_ADDR2BASE(ptr) != ptr);

        chunk = (arena_chunk_t *)CHUNK_ADDR2BASE(ptr);
        pageind = (((uintptr_t)ptr - (uintptr_t)chunk) >> pagesize_2pow);
        mapbits = chunk->map[pageind].bits;
        assert((mapbits & CHUNK_MAP_ALLOCATED) != 0);
        if ((mapbits & CHUNK_MAP_LARGE) == 0) {
                arena_run_t *run = (arena_run_t *)(mapbits & ~pagesize_mask);
                assert(run->magic == ARENA_RUN_MAGIC);
                ret = run->bin->reg_size;
        } else {
                ret = mapbits & ~pagesize_mask;
                assert(ret != 0);
        }

        return (ret);
}

static inline size_t
isalloc(const void *ptr)
{
        size_t ret;
        arena_chunk_t *chunk;

        assert(ptr != NULL);

        chunk = (arena_chunk_t *)CHUNK_ADDR2BASE(ptr);
        if (chunk != ptr) {
                /* Region. */
                assert(chunk->arena->magic == ARENA_MAGIC);

                ret = arena_salloc(ptr);
        } else {
                extent_node_t *node, key;

                /* Chunk (huge allocation). */

                malloc_mutex_lock(&huge_mtx);

                /* Extract from tree of huge allocations. */
                key.addr = __DECONST(void *, ptr);
                node = extent_tree_ad_search(&huge, &key);
                assert(node != NULL);

                ret = node->size;

                malloc_mutex_unlock(&huge_mtx);
        }

        return (ret);
}

static inline void
arena_dalloc_small(arena_t *arena, arena_chunk_t *chunk, void *ptr,
    arena_chunk_map_t *mapelm)
{
        arena_run_t *run;
        arena_bin_t *bin;
        size_t size;

        run = (arena_run_t *)(mapelm->bits & ~pagesize_mask);
        assert(run->magic == ARENA_RUN_MAGIC);
        bin = run->bin;
        size = bin->reg_size;

        if (opt_junk)
                memset(ptr, 0x5a, size);

        arena_run_reg_dalloc(run, bin, ptr, size);
        run->nfree++;

        if (run->nfree == bin->nregs) {
                /* Deallocate run. */
                if (run == bin->runcur)
                        bin->runcur = NULL;
                else if (bin->nregs != 1) {
                        size_t run_pageind = (((uintptr_t)run -
                            (uintptr_t)chunk)) >> pagesize_2pow;
                        arena_chunk_map_t *run_mapelm =
                            &chunk->map[run_pageind];
                        /*
                         * This block's conditional is necessary because if the
                         * run only contains one region, then it never gets
                         * inserted into the non-full runs tree.
                         */
                        arena_run_tree_remove(&bin->runs, run_mapelm);
                }
#ifdef MALLOC_DEBUG
                run->magic = 0;
#endif
                arena_run_dalloc(arena, run, true);
#ifdef MALLOC_STATS
                bin->stats.curruns--;
#endif
        } else if (run->nfree == 1 && run != bin->runcur) {
                /*
                 * Make sure that bin->runcur always refers to the lowest
                 * non-full run, if one exists.
                 */
                if (bin->runcur == NULL)
                        bin->runcur = run;
                else if ((uintptr_t)run < (uintptr_t)bin->runcur) {
                        /* Switch runcur. */
                        if (bin->runcur->nfree > 0) {
                                arena_chunk_t *runcur_chunk =
                                    CHUNK_ADDR2BASE(bin->runcur);
                                size_t runcur_pageind =
                                    (((uintptr_t)bin->runcur -
                                    (uintptr_t)runcur_chunk)) >> pagesize_2pow;
                                arena_chunk_map_t *runcur_mapelm =
                                    &runcur_chunk->map[runcur_pageind];

                                /* Insert runcur. */
                                arena_run_tree_insert(&bin->runs,
                                    runcur_mapelm);
                        }
                        bin->runcur = run;
                } else {
                        size_t run_pageind = (((uintptr_t)run -
                            (uintptr_t)chunk)) >> pagesize_2pow;
                        arena_chunk_map_t *run_mapelm =
                            &chunk->map[run_pageind];

                        assert(arena_run_tree_search(&bin->runs, run_mapelm) ==
                            NULL);
                        arena_run_tree_insert(&bin->runs, run_mapelm);
                }
        }
#ifdef MALLOC_STATS
        arena->stats.allocated_small -= size;
        arena->stats.ndalloc_small++;
#endif
}

static void
arena_dalloc_large(arena_t *arena, arena_chunk_t *chunk, void *ptr)
{
        /* Large allocation. */
        malloc_spin_lock(&arena->lock);

#ifndef MALLOC_STATS
        if (opt_junk)
#endif
        {
                size_t pageind = ((uintptr_t)ptr - (uintptr_t)chunk) >>
                    pagesize_2pow;
                size_t size = chunk->map[pageind].bits & ~pagesize_mask;

#ifdef MALLOC_STATS
                if (opt_junk)
#endif
                        memset(ptr, 0x5a, size);
#ifdef MALLOC_STATS
                arena->stats.allocated_large -= size;
#endif
        }
#ifdef MALLOC_STATS
        arena->stats.ndalloc_large++;
#endif

        arena_run_dalloc(arena, (arena_run_t *)ptr, true);
        malloc_spin_unlock(&arena->lock);
}

static inline void
arena_dalloc(arena_t *arena, arena_chunk_t *chunk, void *ptr)
{
        size_t pageind;
        arena_chunk_map_t *mapelm;

        assert(arena != NULL);
        assert(arena->magic == ARENA_MAGIC);
        assert(chunk->arena == arena);
        assert(ptr != NULL);
        assert(CHUNK_ADDR2BASE(ptr) != ptr);

        pageind = (((uintptr_t)ptr - (uintptr_t)chunk) >> pagesize_2pow);
        mapelm = &chunk->map[pageind];
        assert((mapelm->bits & CHUNK_MAP_ALLOCATED) != 0);
        if ((mapelm->bits & CHUNK_MAP_LARGE) == 0) {
                /* Small allocation. */
                malloc_spin_lock(&arena->lock);
                arena_dalloc_small(arena, chunk, ptr, mapelm);
                malloc_spin_unlock(&arena->lock);
        } else
                arena_dalloc_large(arena, chunk, ptr);
}

static inline void
idalloc(void *ptr)
{
        arena_chunk_t *chunk;

        assert(ptr != NULL);

        chunk = (arena_chunk_t *)CHUNK_ADDR2BASE(ptr);
        if (chunk != ptr)
                arena_dalloc(chunk->arena, chunk, ptr);
        else
                huge_dalloc(ptr);
}

static void
arena_ralloc_large_shrink(arena_t *arena, arena_chunk_t *chunk, void *ptr,
    size_t size, size_t oldsize)
{

        assert(size < oldsize);

        /*
         * Shrink the run, and make trailing pages available for other
         * allocations.
         */
#ifdef MALLOC_BALANCE
        arena_lock_balance(arena);
#else
        malloc_spin_lock(&arena->lock);
#endif
        arena_run_trim_tail(arena, chunk, (arena_run_t *)ptr, oldsize, size,
            true);
#ifdef MALLOC_STATS
        arena->stats.allocated_large -= oldsize - size;
#endif
        malloc_spin_unlock(&arena->lock);
}

static bool
arena_ralloc_large_grow(arena_t *arena, arena_chunk_t *chunk, void *ptr,
    size_t size, size_t oldsize)
{
        size_t pageind = ((uintptr_t)ptr - (uintptr_t)chunk) >> pagesize_2pow;
        size_t npages = oldsize >> pagesize_2pow;

        assert(oldsize == (chunk->map[pageind].bits & ~pagesize_mask));

        /* Try to extend the run. */
        assert(size > oldsize);
#ifdef MALLOC_BALANCE
        arena_lock_balance(arena);
#else
        malloc_spin_lock(&arena->lock);
#endif
        if (pageind + npages < chunk_npages && (chunk->map[pageind+npages].bits
            & CHUNK_MAP_ALLOCATED) == 0 && (chunk->map[pageind+npages].bits &
            ~pagesize_mask) >= size - oldsize) {
                /*
                 * The next run is available and sufficiently large.  Split the
                 * following run, then merge the first part with the existing
                 * allocation.
                 */
                arena_run_split(arena, (arena_run_t *)((uintptr_t)chunk +
                    ((pageind+npages) << pagesize_2pow)), size - oldsize, true,
                    false);

                chunk->map[pageind].bits = size | CHUNK_MAP_LARGE |
                    CHUNK_MAP_ALLOCATED;
                chunk->map[pageind+npages].bits = CHUNK_MAP_LARGE |
                    CHUNK_MAP_ALLOCATED;

#ifdef MALLOC_STATS
                arena->stats.allocated_large += size - oldsize;
#endif
                malloc_spin_unlock(&arena->lock);
                return (false);
        }
        malloc_spin_unlock(&arena->lock);

        return (true);
}

/*
 * Try to resize a large allocation, in order to avoid copying.  This will
 * always fail if growing an object, and the following run is already in use.
 */
static bool
arena_ralloc_large(void *ptr, size_t size, size_t oldsize)
{
        size_t psize;

        psize = PAGE_CEILING(size);
        if (psize == oldsize) {
                /* Same size class. */
                if (opt_junk && size < oldsize) {
                        memset((void *)((uintptr_t)ptr + size), 0x5a, oldsize -
                            size);
                }
                return (false);
        } else {
                arena_chunk_t *chunk;
                arena_t *arena;

                chunk = (arena_chunk_t *)CHUNK_ADDR2BASE(ptr);
                arena = chunk->arena;
                assert(arena->magic == ARENA_MAGIC);

                if (psize < oldsize) {
                        /* Fill before shrinking in order avoid a race. */
                        if (opt_junk) {
                                memset((void *)((uintptr_t)ptr + size), 0x5a,
                                    oldsize - size);
                        }
                        arena_ralloc_large_shrink(arena, chunk, ptr, psize,
                            oldsize);
                        return (false);
                } else {
                        bool ret = arena_ralloc_large_grow(arena, chunk, ptr,
                            psize, oldsize);
                        if (ret == false && opt_zero) {
                                memset((void *)((uintptr_t)ptr + oldsize), 0,
                                    size - oldsize);
                        }
                        return (ret);
                }
        }
}

static void *
arena_ralloc(void *ptr, size_t size, size_t oldsize)
{
        void *ret;
        size_t copysize;

        /* Try to avoid moving the allocation. */
        if (size < small_min) {
                if (oldsize < small_min &&
                    ffs((int)(pow2_ceil(size) >> (TINY_MIN_2POW + 1)))
                    == ffs((int)(pow2_ceil(oldsize) >> (TINY_MIN_2POW + 1))))
                        goto IN_PLACE; /* Same size class. */
        } else if (size <= small_max) {
                if (oldsize >= small_min && oldsize <= small_max &&
                    (QUANTUM_CEILING(size) >> opt_quantum_2pow)
                    == (QUANTUM_CEILING(oldsize) >> opt_quantum_2pow))
                        goto IN_PLACE; /* Same size class. */
        } else if (size <= bin_maxclass) {
                if (oldsize > small_max && oldsize <= bin_maxclass &&
                    pow2_ceil(size) == pow2_ceil(oldsize))
                        goto IN_PLACE; /* Same size class. */
        } else if (oldsize > bin_maxclass && oldsize <= arena_maxclass) {
                assert(size > bin_maxclass);
                if (arena_ralloc_large(ptr, size, oldsize) == false)
                        return (ptr);
        }

        /*
         * If we get here, then size and oldsize are different enough that we
         * need to move the object.  In that case, fall back to allocating new
         * space and copying.
         */
        ret = arena_malloc(choose_arena(), size, false);
        if (ret == NULL)
                return (NULL);

        /* Junk/zero-filling were already done by arena_malloc(). */
        copysize = (size < oldsize) ? size : oldsize;
        memcpy(ret, ptr, copysize);
        idalloc(ptr);
        return (ret);
IN_PLACE:
        if (opt_junk && size < oldsize)
                memset((void *)((uintptr_t)ptr + size), 0x5a, oldsize - size);
        else if (opt_zero && size > oldsize)
                memset((void *)((uintptr_t)ptr + oldsize), 0, size - oldsize);
        return (ptr);
}

static inline void *
iralloc(void *ptr, size_t size)
{
        size_t oldsize;

        assert(ptr != NULL);
        assert(size != 0);

        oldsize = isalloc(ptr);

        if (size <= arena_maxclass)
                return (arena_ralloc(ptr, size, oldsize));
        else
                return (huge_ralloc(ptr, size, oldsize));
}

static bool
arena_new(arena_t *arena)
{
        unsigned i;
        arena_bin_t *bin;
        size_t prev_run_size;

        if (malloc_spin_init(&arena->lock))
                return (true);

#ifdef MALLOC_STATS
        memset(&arena->stats, 0, sizeof(arena_stats_t));
#endif

        /* Initialize chunks. */
        arena_chunk_tree_dirty_new(&arena->chunks_dirty);
        arena->spare = NULL;

        arena->ndirty = 0;

        arena_avail_tree_new(&arena->runs_avail);

#ifdef MALLOC_BALANCE
        arena->contention = 0;
#endif

        /* Initialize bins. */
        prev_run_size = pagesize;

        /* (2^n)-spaced tiny bins. */
        for (i = 0; i < ntbins; i++) {
                bin = &arena->bins[i];
                bin->runcur = NULL;
                arena_run_tree_new(&bin->runs);

                bin->reg_size = (1U << (TINY_MIN_2POW + i));

                prev_run_size = arena_bin_run_size_calc(bin, prev_run_size);

#ifdef MALLOC_STATS
                memset(&bin->stats, 0, sizeof(malloc_bin_stats_t));
#endif
        }

        /* Quantum-spaced bins. */
        for (; i < ntbins + nqbins; i++) {
                bin = &arena->bins[i];
                bin->runcur = NULL;
                arena_run_tree_new(&bin->runs);

                bin->reg_size = quantum * (i - ntbins + 1);

                prev_run_size = arena_bin_run_size_calc(bin, prev_run_size);

#ifdef MALLOC_STATS
                memset(&bin->stats, 0, sizeof(malloc_bin_stats_t));
#endif
        }

        /* (2^n)-spaced sub-page bins. */
        for (; i < ntbins + nqbins + nsbins; i++) {
                bin = &arena->bins[i];
                bin->runcur = NULL;
                arena_run_tree_new(&bin->runs);

                bin->reg_size = (small_max << (i - (ntbins + nqbins) + 1));

                prev_run_size = arena_bin_run_size_calc(bin, prev_run_size);

#ifdef MALLOC_STATS
                memset(&bin->stats, 0, sizeof(malloc_bin_stats_t));
#endif
        }

#ifdef MALLOC_DEBUG
        arena->magic = ARENA_MAGIC;
#endif

        return (false);
}

/* Create a new arena and insert it into the arenas array at index ind. */
static arena_t *
arenas_extend(unsigned ind)
{
        arena_t *ret;

        /* Allocate enough space for trailing bins. */
        ret = (arena_t *)base_alloc(sizeof(arena_t)
            + (sizeof(arena_bin_t) * (ntbins + nqbins + nsbins - 1)));
        if (ret != NULL && arena_new(ret) == false) {
                arenas[ind] = ret;
                return (ret);
        }
        /* Only reached if there is an OOM error. */

        /*
         * OOM here is quite inconvenient to propagate, since dealing with it
         * would require a check for failure in the fast path.  Instead, punt
         * by using arenas[0].  In practice, this is an extremely unlikely
         * failure.
         */
        _malloc_message(_getprogname(),
            ": (malloc) Error initializing arena\n", "", "");
        if (opt_abort)
                abort();

        return (arenas[0]);
}

/*
 * End arena.
 */
/******************************************************************************/
/*
 * Begin general internal functions.
 */

static void *
huge_malloc(size_t size, bool zero)
{
        void *ret;
        size_t csize;
        extent_node_t *node;

        /* Allocate one or more contiguous chunks for this request. */

        csize = CHUNK_CEILING(size);
        if (csize == 0) {
                /* size is large enough to cause size_t wrap-around. */
                return (NULL);
        }

        /* Allocate an extent node with which to track the chunk. */
        node = base_node_alloc();
        if (node == NULL)
                return (NULL);

        ret = chunk_alloc(csize, zero);
        if (ret == NULL) {
                base_node_dealloc(node);
                return (NULL);
        }

        /* Insert node into huge. */
        node->addr = ret;
        node->size = csize;

        malloc_mutex_lock(&huge_mtx);
        extent_tree_ad_insert(&huge, node);
#ifdef MALLOC_STATS
        huge_nmalloc++;
        huge_allocated += csize;
#endif
        malloc_mutex_unlock(&huge_mtx);

        if (zero == false) {
                if (opt_junk)
                        memset(ret, 0xa5, csize);
                else if (opt_zero)
                        memset(ret, 0, csize);
        }

        return (ret);
}

/* Only handles large allocations that require more than chunk alignment. */
static void *
huge_palloc(size_t alignment, size_t size)
{
        void *ret;
        size_t alloc_size, chunk_size, offset;
        extent_node_t *node;

        /*
         * This allocation requires alignment that is even larger than chunk
         * alignment.  This means that huge_malloc() isn't good enough.
         *
         * Allocate almost twice as many chunks as are demanded by the size or
         * alignment, in order to assure the alignment can be achieved, then
         * unmap leading and trailing chunks.
         */
        assert(alignment >= chunksize);

        chunk_size = CHUNK_CEILING(size);

        if (size >= alignment)
                alloc_size = chunk_size + alignment - chunksize;
        else
                alloc_size = (alignment << 1) - chunksize;

        /* Allocate an extent node with which to track the chunk. */
        node = base_node_alloc();
        if (node == NULL)
                return (NULL);

        ret = chunk_alloc(alloc_size, false);
        if (ret == NULL) {
                base_node_dealloc(node);
                return (NULL);
        }

        offset = (uintptr_t)ret & (alignment - 1);
        assert((offset & chunksize_mask) == 0);
        assert(offset < alloc_size);
        if (offset == 0) {
                /* Trim trailing space. */
                chunk_dealloc((void *)((uintptr_t)ret + chunk_size), alloc_size
                    - chunk_size);
        } else {
                size_t trailsize;

                /* Trim leading space. */
                chunk_dealloc(ret, alignment - offset);

                ret = (void *)((uintptr_t)ret + (alignment - offset));

                trailsize = alloc_size - (alignment - offset) - chunk_size;
                if (trailsize != 0) {
                    /* Trim trailing space. */
                    assert(trailsize < alloc_size);
                    chunk_dealloc((void *)((uintptr_t)ret + chunk_size),
                        trailsize);
                }
        }

        /* Insert node into huge. */
        node->addr = ret;
        node->size = chunk_size;

        malloc_mutex_lock(&huge_mtx);
        extent_tree_ad_insert(&huge, node);
#ifdef MALLOC_STATS
        huge_nmalloc++;
        huge_allocated += chunk_size;
#endif
        malloc_mutex_unlock(&huge_mtx);

        if (opt_junk)
                memset(ret, 0xa5, chunk_size);
        else if (opt_zero)
                memset(ret, 0, chunk_size);

        return (ret);
}

static void *
huge_ralloc(void *ptr, size_t size, size_t oldsize)
{
        void *ret;
        size_t copysize;

        /* Avoid moving the allocation if the size class would not change. */
        if (oldsize > arena_maxclass &&
            CHUNK_CEILING(size) == CHUNK_CEILING(oldsize)) {
                if (opt_junk && size < oldsize) {
                        memset((void *)((uintptr_t)ptr + size), 0x5a, oldsize
                            - size);
                } else if (opt_zero && size > oldsize) {
                        memset((void *)((uintptr_t)ptr + oldsize), 0, size
                            - oldsize);
                }
                return (ptr);
        }

        /*
         * If we get here, then size and oldsize are different enough that we
         * need to use a different size class.  In that case, fall back to
         * allocating new space and copying.
         */
        ret = huge_malloc(size, false);
        if (ret == NULL)
                return (NULL);

        copysize = (size < oldsize) ? size : oldsize;
        memcpy(ret, ptr, copysize);
        idalloc(ptr);
        return (ret);
}

static void
huge_dalloc(void *ptr)
{
        extent_node_t *node, key;

        malloc_mutex_lock(&huge_mtx);

        /* Extract from tree of huge allocations. */
        key.addr = ptr;
        node = extent_tree_ad_search(&huge, &key);
        assert(node != NULL);
        assert(node->addr == ptr);
        extent_tree_ad_remove(&huge, node);

#ifdef MALLOC_STATS
        huge_ndalloc++;
        huge_allocated -= node->size;
#endif

        malloc_mutex_unlock(&huge_mtx);

        /* Unmap chunk. */
#ifdef MALLOC_DSS
        if (opt_dss && opt_junk)
                memset(node->addr, 0x5a, node->size);
#endif
        chunk_dealloc(node->addr, node->size);

        base_node_dealloc(node);
}

static void
malloc_print_stats(void)
{

        if (opt_print_stats) {
                char s[UMAX2S_BUFSIZE];
                _malloc_message("___ Begin malloc statistics ___\n", "", "",
                    "");
                _malloc_message("Assertions ",
#ifdef NDEBUG
                    "disabled",
#else
                    "enabled",
#endif
                    "\n", "");
                _malloc_message("Boolean MALLOC_OPTIONS: ",
                    opt_abort ? "A" : "a", "", "");
#ifdef MALLOC_DSS
                _malloc_message(opt_dss ? "D" : "d", "", "", "");
#endif
                _malloc_message(opt_junk ? "J" : "j", "", "", "");
#ifdef MALLOC_DSS
                _malloc_message(opt_mmap ? "M" : "m", "", "", "");
#endif
                _malloc_message(opt_utrace ? "PU" : "Pu",
                    opt_sysv ? "V" : "v",
                    opt_xmalloc ? "X" : "x",
                    opt_zero ? "Z\n" : "z\n");

                _malloc_message("CPUs: ", umax2s(ncpus, s), "\n", "");
                _malloc_message("Max arenas: ", umax2s(narenas, s), "\n", "");
#ifdef MALLOC_BALANCE
                _malloc_message("Arena balance threshold: ",
                    umax2s(opt_balance_threshold, s), "\n", "");
#endif
                _malloc_message("Pointer size: ", umax2s(sizeof(void *), s),
                    "\n", "");
                _malloc_message("Quantum size: ", umax2s(quantum, s), "\n", "");
                _malloc_message("Max small size: ", umax2s(small_max, s), "\n",
                    "");
                _malloc_message("Max dirty pages per arena: ",
                    umax2s(opt_dirty_max, s), "\n", "");

                _malloc_message("Chunk size: ", umax2s(chunksize, s), "", "");
                _malloc_message(" (2^", umax2s(opt_chunk_2pow, s), ")\n", "");

#ifdef MALLOC_STATS
                {
                        size_t allocated, mapped;
#ifdef MALLOC_BALANCE
                        uint64_t nbalance = 0;
#endif
                        unsigned i;
                        arena_t *arena;

                        /* Calculate and print allocated/mapped stats. */

                        /* arenas. */
                        for (i = 0, allocated = 0; i < narenas; i++) {
                                if (arenas[i] != NULL) {
                                        malloc_spin_lock(&arenas[i]->lock);
                                        allocated +=
                                            arenas[i]->stats.allocated_small;
                                        allocated +=
                                            arenas[i]->stats.allocated_large;
#ifdef MALLOC_BALANCE
                                        nbalance += arenas[i]->stats.nbalance;
#endif
                                        malloc_spin_unlock(&arenas[i]->lock);
                                }
                        }

                        /* huge/base. */
                        malloc_mutex_lock(&huge_mtx);
                        allocated += huge_allocated;
                        mapped = stats_chunks.curchunks * chunksize;
                        malloc_mutex_unlock(&huge_mtx);

                        malloc_mutex_lock(&base_mtx);
                        mapped += base_mapped;
                        malloc_mutex_unlock(&base_mtx);

                        malloc_printf("Allocated: %zu, mapped: %zu\n",
                            allocated, mapped);

#ifdef MALLOC_BALANCE
                        malloc_printf("Arena balance reassignments: %llu\n",
                            nbalance);
#endif

                        /* Print chunk stats. */
                        {
                                chunk_stats_t chunks_stats;

                                malloc_mutex_lock(&huge_mtx);
                                chunks_stats = stats_chunks;
                                malloc_mutex_unlock(&huge_mtx);

                                malloc_printf("chunks: nchunks   "
                                    "highchunks    curchunks\n");
                                malloc_printf("  %13llu%13lu%13lu\n",
                                    chunks_stats.nchunks,
                                    chunks_stats.highchunks,
                                    chunks_stats.curchunks);
                        }

                        /* Print chunk stats. */
                        malloc_printf(
                            "huge: nmalloc      ndalloc    allocated\n");
                        malloc_printf(" %12llu %12llu %12zu\n",
                            huge_nmalloc, huge_ndalloc, huge_allocated);

                        /* Print stats for each arena. */
                        for (i = 0; i < narenas; i++) {
                                arena = arenas[i];
                                if (arena != NULL) {
                                        malloc_printf(
                                            "\narenas[%u]:\n", i);
                                        malloc_spin_lock(&arena->lock);
                                        stats_print(arena);
                                        malloc_spin_unlock(&arena->lock);
                                }
                        }
                }
#endif /* #ifdef MALLOC_STATS */
                _malloc_message("--- End malloc statistics ---\n", "", "", "");
        }
}

/*
 * FreeBSD's pthreads implementation calls malloc(3), so the malloc
 * implementation has to take pains to avoid infinite recursion during
 * initialization.
 */
static inline bool
malloc_init(void)
{

        if (malloc_initialized == false)
                return (malloc_init_hard());

        return (false);
}

static bool
malloc_init_hard(void)
{
        unsigned i;
        int linklen;
        char buf[PATH_MAX + 1];
        const char *opts;

        malloc_mutex_lock(&init_lock);
        if (malloc_initialized) {
                /*
                 * Another thread initialized the allocator before this one
                 * acquired init_lock.
                 */
                malloc_mutex_unlock(&init_lock);
                return (false);
        }

        /* Get number of CPUs. */
        {
                int mib[2];
                size_t len;

                mib[0] = CTL_HW;
                mib[1] = HW_NCPU;
                len = sizeof(ncpus);
                if (sysctl(mib, 2, &ncpus, &len, (void *) 0, 0) == -1) {
                        /* Error. */
                        ncpus = 1;
                }
        }

        /* Get page size. */
        {
                long result;

                result = sysconf(_SC_PAGESIZE);
                assert(result != -1);
                pagesize = (unsigned)result;

                /*
                 * We assume that pagesize is a power of 2 when calculating
                 * pagesize_mask and pagesize_2pow.
                 */
                assert(((result - 1) & result) == 0);
                pagesize_mask = result - 1;
                pagesize_2pow = ffs((int)result) - 1;
        }

        for (i = 0; i < 3; i++) {
                unsigned j;

                /* Get runtime configuration. */
                switch (i) {
                case 0:
                        if ((linklen = readlink("/etc/malloc.conf", buf,
                                                sizeof(buf) - 1)) != -1) {
                                /*
                                 * Use the contents of the "/etc/malloc.conf"
                                 * symbolic link's name.
                                 */
                                buf[linklen] = '\0';
                                opts = buf;
                        } else {
                                /* No configuration specified. */
                                buf[0] = '\0';
                                opts = buf;
                        }
                        break;
                case 1:
                        if (issetugid() == 0 && (opts =
                            getenv("MALLOC_OPTIONS")) != NULL) {
                                /*
                                 * Do nothing; opts is already initialized to
                                 * the value of the MALLOC_OPTIONS environment
                                 * variable.
                                 */
                        } else {
                                /* No configuration specified. */
                                buf[0] = '\0';
                                opts = buf;
                        }
                        break;
                case 2:
                        if (_malloc_options != NULL) {
                                /*
                                 * Use options that were compiled into the
                                 * program.
                                 */
                                opts = _malloc_options;
                        } else {
                                /* No configuration specified. */
                                buf[0] = '\0';
                                opts = buf;
                        }
                        break;
                default:
                        /* NOTREACHED */
                        assert(false);
                }

                for (j = 0; opts[j] != '\0'; j++) {
                        unsigned k, nreps;
                        bool nseen;

                        /* Parse repetition count, if any. */
                        for (nreps = 0, nseen = false;; j++, nseen = true) {
                                switch (opts[j]) {
                                        case '0': case '1': case '2': case '3':
                                        case '4': case '5': case '6': case '7':
                                        case '8': case '9':
                                                nreps *= 10;
                                                nreps += opts[j] - '0';
                                                break;
                                        default:
                                                goto MALLOC_OUT;
                                }
                        }
MALLOC_OUT:
                        if (nseen == false)
                                nreps = 1;

                        for (k = 0; k < nreps; k++) {
                                switch (opts[j]) {
                                case 'a':
                                        opt_abort = false;
                                        break;
                                case 'A':
                                        opt_abort = true;
                                        break;
                                case 'b':
#ifdef MALLOC_BALANCE
                                        opt_balance_threshold >>= 1;
#endif
                                        break;
                                case 'B':
#ifdef MALLOC_BALANCE
                                        if (opt_balance_threshold == 0)
                                                opt_balance_threshold = 1;
                                        else if ((opt_balance_threshold << 1)
                                            > opt_balance_threshold)
                                                opt_balance_threshold <<= 1;
#endif
                                        break;
                                case 'd':
#ifdef MALLOC_DSS
                                        opt_dss = false;
#endif
                                        break;
                                case 'D':
#ifdef MALLOC_DSS
                                        opt_dss = true;
#endif
                                        break;
                                case 'f':
                                        opt_dirty_max >>= 1;
                                        break;
                                case 'F':
                                        if (opt_dirty_max == 0)
                                                opt_dirty_max = 1;
                                        else if ((opt_dirty_max << 1) != 0)
                                                opt_dirty_max <<= 1;
                                        break;
                                case 'h':
                                        /* Compatibility hack for RELENG_7. */
                                        opt_dirty_max = DIRTY_MAX_DEFAULT;
                                        break;
                                case 'H':
                                        /* Compatibility hack for RELENG_7. */
                                        opt_dirty_max = 0;
                                        break;
                                case 'j':
                                        opt_junk = false;
                                        break;
                                case 'J':
                                        opt_junk = true;
                                        break;
                                case 'k':
                                        /*
                                         * Chunks always require at least one
                                         * header page, so chunks can never be
                                         * smaller than two pages.
                                         */
                                        if (opt_chunk_2pow > pagesize_2pow + 1)
                                                opt_chunk_2pow--;
                                        break;
                                case 'K':
                                        if (opt_chunk_2pow + 1 <
                                            (sizeof(size_t) << 3))
                                                opt_chunk_2pow++;
                                        break;
                                case 'm':
#ifdef MALLOC_DSS
                                        opt_mmap = false;
#endif
                                        break;
                                case 'M':
#ifdef MALLOC_DSS
                                        opt_mmap = true;
#endif
                                        break;
                                case 'n':
                                        opt_narenas_lshift--;
                                        break;
                                case 'N':
                                        opt_narenas_lshift++;
                                        break;
                                case 'p':
                                        opt_print_stats = false;
                                        break;
                                case 'P':
                                        opt_print_stats = true;
                                        break;
                                case 'q':
                                        if (opt_quantum_2pow > QUANTUM_2POW_MIN)
                                                opt_quantum_2pow--;
                                        break;
                                case 'Q':
                                        if (opt_quantum_2pow < pagesize_2pow -
                                            1)
                                                opt_quantum_2pow++;
                                        break;
                                case 's':
                                        if (opt_small_max_2pow >
                                            QUANTUM_2POW_MIN)
                                                opt_small_max_2pow--;
                                        break;
                                case 'S':
                                        if (opt_small_max_2pow < pagesize_2pow
                                            - 1)
                                                opt_small_max_2pow++;
                                        break;
                                case 'u':
                                        opt_utrace = false;
                                        break;
                                case 'U':
                                        opt_utrace = true;
                                        break;
                                case 'v':
                                        opt_sysv = false;
                                        break;
                                case 'V':
                                        opt_sysv = true;
                                        break;
                                case 'x':
                                        opt_xmalloc = false;
                                        break;
                                case 'X':
                                        opt_xmalloc = true;
                                        break;
                                case 'z':
                                        opt_zero = false;
                                        break;
                                case 'Z':
                                        opt_zero = true;
                                        break;
                                default: {
                                        char cbuf[2];

                                        cbuf[0] = opts[j];
                                        cbuf[1] = '\0';
                                        _malloc_message(_getprogname(),
                                            ": (malloc) Unsupported character "
                                            "in malloc options: '", cbuf,
                                            "'\n");
                                }
                                }
                        }
                }
        }

#ifdef MALLOC_DSS
        /* Make sure that there is some method for acquiring memory. */
        if (opt_dss == false && opt_mmap == false)
                opt_mmap = true;
#endif

        /* Take care to call atexit() only once. */
        if (opt_print_stats) {
                /* Print statistics at exit. */
                atexit(malloc_print_stats);
        }

        /* Set variables according to the value of opt_small_max_2pow. */
        if (opt_small_max_2pow < opt_quantum_2pow)
                opt_small_max_2pow = opt_quantum_2pow;
        small_max = (1U << opt_small_max_2pow);

        /* Set bin-related variables. */
        bin_maxclass = (pagesize >> 1);
        assert(opt_quantum_2pow >= TINY_MIN_2POW);
        ntbins = opt_quantum_2pow - TINY_MIN_2POW;
        assert(ntbins <= opt_quantum_2pow);
        nqbins = (small_max >> opt_quantum_2pow);
        nsbins = pagesize_2pow - opt_small_max_2pow - 1;

        /* Set variables according to the value of opt_quantum_2pow. */
        quantum = (1U << opt_quantum_2pow);
        quantum_mask = quantum - 1;
        if (ntbins > 0)
                small_min = (quantum >> 1) + 1;
        else
                small_min = 1;
        assert(small_min <= quantum);

        /* Set variables according to the value of opt_chunk_2pow. */
        chunksize = (1LU << opt_chunk_2pow);
        chunksize_mask = chunksize - 1;
        chunk_npages = (chunksize >> pagesize_2pow);
        {
                size_t header_size;

                /*
                 * Compute the header size such that it is large
                 * enough to contain the page map and enough nodes for the
                 * worst case: one node per non-header page plus one extra for
                 * situations where we briefly have one more node allocated
                 * than we will need.
                 */
                header_size = sizeof(arena_chunk_t) +
                    (sizeof(arena_chunk_map_t) * (chunk_npages - 1));
                arena_chunk_header_npages = (header_size >> pagesize_2pow) +
                    ((header_size & pagesize_mask) != 0);
        }
        arena_maxclass = chunksize - (arena_chunk_header_npages <<
            pagesize_2pow);

        UTRACE(0, 0, 0);

#ifdef MALLOC_STATS
        memset(&stats_chunks, 0, sizeof(chunk_stats_t));
#endif

        /* Various sanity checks that regard configuration. */
        assert(quantum >= sizeof(void *));
        assert(quantum <= pagesize);
        assert(chunksize >= pagesize);
        assert(quantum * 4 <= chunksize);

        /* Initialize chunks data. */
        malloc_mutex_init(&huge_mtx);
        extent_tree_ad_new(&huge);
#ifdef MALLOC_DSS
        malloc_mutex_init(&dss_mtx);
        dss_base = sbrk(0);
        dss_prev = dss_base;
        dss_max = dss_base;
        extent_tree_szad_new(&dss_chunks_szad);
        extent_tree_ad_new(&dss_chunks_ad);
#endif
#ifdef MALLOC_STATS
        huge_nmalloc = 0;
        huge_ndalloc = 0;
        huge_allocated = 0;
#endif

        /* Initialize base allocation data structures. */
#ifdef MALLOC_STATS
        base_mapped = 0;
#endif
#ifdef MALLOC_DSS
        /*
         * Allocate a base chunk here, since it doesn't actually have to be
         * chunk-aligned.  Doing this before allocating any other chunks allows
         * the use of space that would otherwise be wasted.
         */
        if (opt_dss)
                base_pages_alloc(0);
#endif
        base_nodes = NULL;
        malloc_mutex_init(&base_mtx);

        if (ncpus > 1) {
                /*
                 * For SMP systems, create four times as many arenas as there
                 * are CPUs by default.
                 */
                opt_narenas_lshift += 2;
        }

        /* Determine how many arenas to use. */
        narenas = ncpus;
        if (opt_narenas_lshift > 0) {
                if ((narenas << opt_narenas_lshift) > narenas)
                        narenas <<= opt_narenas_lshift;
                /*
                 * Make sure not to exceed the limits of what base_alloc() can
                 * handle.
                 */
                if (narenas * sizeof(arena_t *) > chunksize)
                        narenas = chunksize / sizeof(arena_t *);
        } else if (opt_narenas_lshift < 0) {
                if ((narenas >> -opt_narenas_lshift) < narenas)
                        narenas >>= -opt_narenas_lshift;
                /* Make sure there is at least one arena. */
                if (narenas == 0)
                        narenas = 1;
        }
#ifdef MALLOC_BALANCE
        assert(narenas != 0);
        for (narenas_2pow = 0;
             (narenas >> (narenas_2pow + 1)) != 0;
             narenas_2pow++);
#endif

#ifdef NO_TLS
        if (narenas > 1) {
                static const unsigned primes[] = {1, 3, 5, 7, 11, 13, 17, 19,
                    23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83,
                    89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149,
                    151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211,
                    223, 227, 229, 233, 239, 241, 251, 257, 263};
                unsigned nprimes, parenas;

                /*
                 * Pick a prime number of hash arenas that is more than narenas
                 * so that direct hashing of pthread_self() pointers tends to
                 * spread allocations evenly among the arenas.
                 */
                assert((narenas & 1) == 0); /* narenas must be even. */
                nprimes = (sizeof(primes) >> SIZEOF_INT_2POW);
                parenas = primes[nprimes - 1]; /* In case not enough primes. */
                for (i = 1; i < nprimes; i++) {
                        if (primes[i] > narenas) {
                                parenas = primes[i];
                                break;
                        }
                }
                narenas = parenas;
        }
#endif

#ifndef NO_TLS
#  ifndef MALLOC_BALANCE
        next_arena = 0;
#  endif
#endif

        /* Allocate and initialize arenas. */
        arenas = (arena_t **)base_alloc(sizeof(arena_t *) * narenas);
        if (arenas == NULL) {
                malloc_mutex_unlock(&init_lock);
                return (true);
        }
        /*
         * Zero the array.  In practice, this should always be pre-zeroed,
         * since it was just mmap()ed, but let's be sure.
         */
        memset(arenas, 0, sizeof(arena_t *) * narenas);

        /*
         * Initialize one arena here.  The rest are lazily created in
         * choose_arena_hard().
         */
        arenas_extend(0);
        if (arenas[0] == NULL) {
                malloc_mutex_unlock(&init_lock);
                return (true);
        }
#ifndef NO_TLS
        /*
         * Assign the initial arena to the initial thread, in order to avoid
         * spurious creation of an extra arena if the application switches to
         * threaded mode.
         */
        arenas_map = arenas[0];
#endif
        /*
         * Seed here for the initial thread, since choose_arena_hard() is only
         * called for other threads.  The seed value doesn't really matter.
         */
#ifdef MALLOC_BALANCE
        SPRN(balance, 42);
#endif

        malloc_spin_init(&arenas_lock);

        malloc_initialized = true;
        malloc_mutex_unlock(&init_lock);
        return (false);
}

/*
 * End general internal functions.
 */
/******************************************************************************/
/*
 * Begin malloc(3)-compatible functions.
 */

void *
malloc(size_t size)
{
        void *ret;

        if (malloc_init()) {
                ret = NULL;
                goto RETURN;
        }

        if (size == 0) {
                if (opt_sysv == false)
                        size = 1;
                else {
                        ret = NULL;
                        goto RETURN;
                }
        }

        ret = imalloc(size);

RETURN:
        if (ret == NULL) {
                if (opt_xmalloc) {
                        _malloc_message(_getprogname(),
                            ": (malloc) Error in malloc(): out of memory\n", "",
                            "");
                        abort();
                }
                errno = ENOMEM;
        }

        UTRACE(0, size, ret);
        return (ret);
}

int
posix_memalign(void **memptr, size_t alignment, size_t size)
{
        int ret;
        void *result;

        if (malloc_init())
                result = NULL;
        else {
                /* Make sure that alignment is a large enough power of 2. */
                if (((alignment - 1) & alignment) != 0
                    || alignment < sizeof(void *)) {
                        if (opt_xmalloc) {
                                _malloc_message(_getprogname(),
                                    ": (malloc) Error in posix_memalign(): "
                                    "invalid alignment\n", "", "");
                                abort();
                        }
                        result = NULL;
                        ret = EINVAL;
                        goto RETURN;
                }

                result = ipalloc(alignment, size);
        }

        if (result == NULL) {
                if (opt_xmalloc) {
                        _malloc_message(_getprogname(),
                        ": (malloc) Error in posix_memalign(): out of memory\n",
                        "", "");
                        abort();
                }
                ret = ENOMEM;
                goto RETURN;
        }

        *memptr = result;
        ret = 0;

RETURN:
        UTRACE(0, size, result);
        return (ret);
}

void *
calloc(size_t num, size_t size)
{
        void *ret;
        size_t num_size;

        if (malloc_init()) {
                num_size = 0;
                ret = NULL;
                goto RETURN;
        }

        num_size = num * size;
        if (num_size == 0) {
                if ((opt_sysv == false) && ((num == 0) || (size == 0)))
                        num_size = 1;
                else {
                        ret = NULL;
                        goto RETURN;
                }
        /*
         * Try to avoid division here.  We know that it isn't possible to
         * overflow during multiplication if neither operand uses any of the
         * most significant half of the bits in a size_t.
         */
        } else if (((num | size) & (SIZE_T_MAX << (sizeof(size_t) << 2)))
            && (num_size / size != num)) {
                /* size_t overflow. */
                ret = NULL;
                goto RETURN;
        }

        ret = icalloc(num_size);

RETURN:
        if (ret == NULL) {
                if (opt_xmalloc) {
                        _malloc_message(_getprogname(),
                            ": (malloc) Error in calloc(): out of memory\n", "",
                            "");
                        abort();
                }
                errno = ENOMEM;
        }

        UTRACE(0, num_size, ret);
        return (ret);
}

void *
realloc(void *ptr, size_t size)
{
        void *ret;

        if (size == 0) {
                if (opt_sysv == false)
                        size = 1;
                else {
                        if (ptr != NULL)
                                idalloc(ptr);
                        ret = NULL;
                        goto RETURN;
                }
        }

        if (ptr != NULL) {
                assert(malloc_initialized);

                ret = iralloc(ptr, size);

                if (ret == NULL) {
                        if (opt_xmalloc) {
                                _malloc_message(_getprogname(),
                                    ": (malloc) Error in realloc(): out of "
                                    "memory\n", "", "");
                                abort();
                        }
                        errno = ENOMEM;
                }
        } else {
                if (malloc_init())
                        ret = NULL;
                else
                        ret = imalloc(size);

                if (ret == NULL) {
                        if (opt_xmalloc) {
                                _malloc_message(_getprogname(),
                                    ": (malloc) Error in realloc(): out of "
                                    "memory\n", "", "");
                                abort();
                        }
                        errno = ENOMEM;
                }
        }

RETURN:
        UTRACE(ptr, size, ret);
        return (ret);
}

void
free(void *ptr)
{

        UTRACE(ptr, 0, 0);
        if (ptr != NULL) {
                assert(malloc_initialized);

                idalloc(ptr);
        }
}

/*
 * End malloc(3)-compatible functions.
 */
/******************************************************************************/
/*
 * Begin non-standard functions.
 */

size_t
malloc_usable_size(const void *ptr)
{

        assert(ptr != NULL);

        return (isalloc(ptr));
}

/*
 * End non-standard functions.
 */

/*
 * We provide an unpublished interface in order to receive notifications from
 * the pthreads library whenever a thread exits.  This allows us to clean up
 * thread caches.
 */
void
_malloc_thread_cleanup(void)
{
}

/******************************************************************************/
/*
 * Begin library-private functions, used by threading libraries for protection
 * of malloc during fork().  These functions are only called if the program is
 * running in threaded mode, so there is no need to check whether the program
 * is threaded here.
 */

void
_malloc_prefork(void)
{
        unsigned i;

        /* Acquire all mutexes in a safe order. */

        malloc_spin_lock(&arenas_lock);
        for (i = 0; i < narenas; i++) {
                if (arenas[i] != NULL)
                        malloc_spin_lock(&arenas[i]->lock);
        }
        malloc_spin_unlock(&arenas_lock);

        malloc_mutex_lock(&base_mtx);

        malloc_mutex_lock(&huge_mtx);

#ifdef MALLOC_DSS
        malloc_mutex_lock(&dss_mtx);
#endif
}

void
_malloc_postfork(void)
{
        unsigned i;

        /* Release all mutexes, now that fork() has completed. */

#ifdef MALLOC_DSS
        malloc_mutex_unlock(&dss_mtx);
#endif

        malloc_mutex_unlock(&huge_mtx);

        malloc_mutex_unlock(&base_mtx);

        malloc_spin_lock(&arenas_lock);
        for (i = 0; i < narenas; i++) {
                if (arenas[i] != NULL)
                        malloc_spin_unlock(&arenas[i]->lock);
        }
        malloc_spin_unlock(&arenas_lock);
}

/*
 * End library-private functions.
 */
/******************************************************************************/