2 * Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC.
3 * Copyright (C) 2007 The Regents of the University of California.
4 * Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
5 * Written by Brian Behlendorf <behlendorf1@llnl.gov>.
8 * This file is part of the SPL, Solaris Porting Layer.
9 * For details, see <http://zfsonlinux.org/>.
11 * The SPL is free software; you can redistribute it and/or modify it
12 * under the terms of the GNU General Public License as published by the
13 * Free Software Foundation; either version 2 of the License, or (at your
14 * option) any later version.
16 * The SPL is distributed in the hope that it will be useful, but WITHOUT
17 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
18 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
21 * You should have received a copy of the GNU General Public License along
22 * with the SPL. If not, see <http://www.gnu.org/licenses/>.
29 #include <linux/sched.h>
30 #include <linux/vmalloc.h>
32 typedef struct vmem { } vmem_t;
34 extern vmem_t *heap_arena;
35 extern vmem_t *zio_alloc_arena;
36 extern vmem_t *zio_arena;
38 extern size_t vmem_size(vmem_t *vmp, int typemask);
41 * Memory allocation interfaces
43 #define VMEM_ALLOC 0x01
44 #define VMEM_FREE 0x02
47 #define VMALLOC_TOTAL (VMALLOC_END - VMALLOC_START)
51 * vmem_* is an interface to a low level arena-based memory allocator on
52 * Illumos that is used to allocate virtual address space. The kmem SLAB
53 * allocator allocates slabs from it. Then the generic allocation functions
54 * kmem_{alloc,zalloc,free}() are layered on top of SLAB allocators.
56 * On Linux, the primary means of doing allocations is via kmalloc(), which
57 * is similarly layered on top of something called the buddy allocator. The
58 * buddy allocator is not available to kernel modules, it uses physical
59 * memory addresses rather than virtual memory addresses and is prone to
62 * Linux sets aside a relatively small address space for in-kernel virtual
63 * memory from which allocations can be done using vmalloc(). It might seem
64 * like a good idea to use vmalloc() to implement something similar to
65 * Illumos' allocator. However, this has the following problems:
67 * 1. Page directory table allocations are hard coded to use GFP_KERNEL.
68 * Consequently, any KM_PUSHPAGE or KM_NOSLEEP allocations done using
69 * vmalloc() will not have proper semantics.
71 * 2. Address space exhaustion is a real issue on 32-bit platforms where
72 * only a few 100MB are available. The kernel will handle it by spinning
73 * when it runs out of address space.
75 * 3. All vmalloc() allocations and frees are protected by a single global
76 * lock which serializes all allocations.
78 * 4. Accessing /proc/meminfo and /proc/vmallocinfo will iterate the entire
79 * list. The former will sum the allocations while the latter will print
80 * them to user space in a way that user space can keep the lock held
81 * indefinitely. When the total number of mapped allocations is large
82 * (several 100,000) a large amount of time will be spent waiting on locks.
84 * 5. Linux has a wait_on_bit() locking primitive that assumes physical
85 * memory is used, it simply does not work on virtual memory. Certain
86 * Linux structures (e.g. the superblock) use them and might be embedded
87 * into a structure from Illumos. This makes using Linux virtual memory
88 * unsafe in certain situations.
90 * It follows that we cannot obtain identical semantics to those on Illumos.
91 * Consequently, we implement the kmem_{alloc,zalloc,free}() functions in
92 * such a way that they can be used as drop-in replacements for small vmem_*
93 * allocations (8MB in size or smaller) and map vmem_{alloc,zalloc,free}()
97 #define vmem_alloc(sz, fl) spl_vmem_alloc((sz), (fl), __func__, __LINE__)
98 #define vmem_zalloc(sz, fl) spl_vmem_zalloc((sz), (fl), __func__, __LINE__)
99 #define vmem_free(ptr, sz) spl_vmem_free((ptr), (sz))
100 #define vmem_qcache_reap(ptr) ((void)0)
102 extern void *spl_vmem_alloc(size_t sz, int fl, const char *func, int line);
103 extern void *spl_vmem_zalloc(size_t sz, int fl, const char *func, int line);
104 extern void spl_vmem_free(const void *ptr, size_t sz);
106 int spl_vmem_init(void);
107 void spl_vmem_fini(void);
109 #endif /* _SPL_VMEM_H */