MFC r217226:

[FreeBSD/releng/8.2.git] / sys / vm / vm_object.c

/*-
 * Copyright (c) 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * The Mach Operating System project at Carnegie-Mellon University.
 *
 * 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, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``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 REGENTS OR CONTRIBUTORS 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.
 *
 *      from: @(#)vm_object.c   8.5 (Berkeley) 3/22/94
 *
 *
 * Copyright (c) 1987, 1990 Carnegie-Mellon University.
 * All rights reserved.
 *
 * Authors: Avadis Tevanian, Jr., Michael Wayne Young
 *
 * Permission to use, copy, modify and distribute this software and
 * its documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 *
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
 * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 *
 * Carnegie Mellon requests users of this software to return to
 *
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 *
 * any improvements or extensions that they make and grant Carnegie the
 * rights to redistribute these changes.
 */

/*
 *      Virtual memory object module.
 */

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

#include "opt_vm.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/lock.h>
#include <sys/mman.h>
#include <sys/mount.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/mutex.h>
#include <sys/proc.h>           /* for curproc, pageproc */
#include <sys/socket.h>
#include <sys/resourcevar.h>
#include <sys/vnode.h>
#include <sys/vmmeter.h>
#include <sys/sx.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_pageout.h>
#include <vm/vm_pager.h>
#include <vm/swap_pager.h>
#include <vm/vm_kern.h>
#include <vm/vm_extern.h>
#include <vm/vm_reserv.h>
#include <vm/uma.h>

static int msync_flush_flags = 0;
SYSCTL_INT(_vm, OID_AUTO, msync_flush_flags, CTLFLAG_RW, &msync_flush_flags, 0,
    "Does nothing; kept for backward compatibility");

static int old_msync;
SYSCTL_INT(_vm, OID_AUTO, old_msync, CTLFLAG_RW, &old_msync, 0,
    "Use old (insecure) msync behavior");

static int      vm_object_page_collect_flush(vm_object_t object, vm_page_t p,
                    int pagerflags);
static void     vm_object_qcollapse(vm_object_t object);
static void     vm_object_vndeallocate(vm_object_t object);

/*
 *      Virtual memory objects maintain the actual data
 *      associated with allocated virtual memory.  A given
 *      page of memory exists within exactly one object.
 *
 *      An object is only deallocated when all "references"
 *      are given up.  Only one "reference" to a given
 *      region of an object should be writeable.
 *
 *      Associated with each object is a list of all resident
 *      memory pages belonging to that object; this list is
 *      maintained by the "vm_page" module, and locked by the object's
 *      lock.
 *
 *      Each object also records a "pager" routine which is
 *      used to retrieve (and store) pages to the proper backing
 *      storage.  In addition, objects may be backed by other
 *      objects from which they were virtual-copied.
 *
 *      The only items within the object structure which are
 *      modified after time of creation are:
 *              reference count         locked by object's lock
 *              pager routine           locked by object's lock
 *
 */

struct object_q vm_object_list;
struct mtx vm_object_list_mtx;  /* lock for object list and count */

struct vm_object kernel_object_store;
struct vm_object kmem_object_store;

SYSCTL_NODE(_vm_stats, OID_AUTO, object, CTLFLAG_RD, 0, "VM object stats");

static long object_collapses;
SYSCTL_LONG(_vm_stats_object, OID_AUTO, collapses, CTLFLAG_RD,
    &object_collapses, 0, "VM object collapses");

static long object_bypasses;
SYSCTL_LONG(_vm_stats_object, OID_AUTO, bypasses, CTLFLAG_RD,
    &object_bypasses, 0, "VM object bypasses");

static uma_zone_t obj_zone;

static int vm_object_zinit(void *mem, int size, int flags);

#ifdef INVARIANTS
static void vm_object_zdtor(void *mem, int size, void *arg);

static void
vm_object_zdtor(void *mem, int size, void *arg)
{
        vm_object_t object;

        object = (vm_object_t)mem;
        KASSERT(TAILQ_EMPTY(&object->memq),
            ("object %p has resident pages",
            object));
#if VM_NRESERVLEVEL > 0
        KASSERT(LIST_EMPTY(&object->rvq),
            ("object %p has reservations",
            object));
#endif
        KASSERT(object->cache == NULL,
            ("object %p has cached pages",
            object));
        KASSERT(object->paging_in_progress == 0,
            ("object %p paging_in_progress = %d",
            object, object->paging_in_progress));
        KASSERT(object->resident_page_count == 0,
            ("object %p resident_page_count = %d",
            object, object->resident_page_count));
        KASSERT(object->shadow_count == 0,
            ("object %p shadow_count = %d",
            object, object->shadow_count));
}
#endif

static int
vm_object_zinit(void *mem, int size, int flags)
{
        vm_object_t object;

        object = (vm_object_t)mem;
        bzero(&object->mtx, sizeof(object->mtx));
        VM_OBJECT_LOCK_INIT(object, "standard object");

        /* These are true for any object that has been freed */
        object->paging_in_progress = 0;
        object->resident_page_count = 0;
        object->shadow_count = 0;
        return (0);
}

void
_vm_object_allocate(objtype_t type, vm_pindex_t size, vm_object_t object)
{

        TAILQ_INIT(&object->memq);
        LIST_INIT(&object->shadow_head);

        object->root = NULL;
        object->type = type;
        object->size = size;
        object->generation = 1;
        object->ref_count = 1;
        object->memattr = VM_MEMATTR_DEFAULT;
        object->flags = 0;
        object->uip = NULL;
        object->charge = 0;
        if ((object->type == OBJT_DEFAULT) || (object->type == OBJT_SWAP))
                object->flags = OBJ_ONEMAPPING;
        object->pg_color = 0;
        object->handle = NULL;
        object->backing_object = NULL;
        object->backing_object_offset = (vm_ooffset_t) 0;
#if VM_NRESERVLEVEL > 0
        LIST_INIT(&object->rvq);
#endif
        object->cache = NULL;

        mtx_lock(&vm_object_list_mtx);
        TAILQ_INSERT_TAIL(&vm_object_list, object, object_list);
        mtx_unlock(&vm_object_list_mtx);
}

/*
 *      vm_object_init:
 *
 *      Initialize the VM objects module.
 */
void
vm_object_init(void)
{
        TAILQ_INIT(&vm_object_list);
        mtx_init(&vm_object_list_mtx, "vm object_list", NULL, MTX_DEF);
        
        VM_OBJECT_LOCK_INIT(&kernel_object_store, "kernel object");
        _vm_object_allocate(OBJT_PHYS, OFF_TO_IDX(VM_MAX_KERNEL_ADDRESS - VM_MIN_KERNEL_ADDRESS),
            kernel_object);
#if VM_NRESERVLEVEL > 0
        kernel_object->flags |= OBJ_COLORED;
        kernel_object->pg_color = (u_short)atop(VM_MIN_KERNEL_ADDRESS);
#endif

        VM_OBJECT_LOCK_INIT(&kmem_object_store, "kmem object");
        _vm_object_allocate(OBJT_PHYS, OFF_TO_IDX(VM_MAX_KERNEL_ADDRESS - VM_MIN_KERNEL_ADDRESS),
            kmem_object);
#if VM_NRESERVLEVEL > 0
        kmem_object->flags |= OBJ_COLORED;
        kmem_object->pg_color = (u_short)atop(VM_MIN_KERNEL_ADDRESS);
#endif

        /*
         * The lock portion of struct vm_object must be type stable due
         * to vm_pageout_fallback_object_lock locking a vm object
         * without holding any references to it.
         */
        obj_zone = uma_zcreate("VM OBJECT", sizeof (struct vm_object), NULL,
#ifdef INVARIANTS
            vm_object_zdtor,
#else
            NULL,
#endif
            vm_object_zinit, NULL, UMA_ALIGN_PTR, UMA_ZONE_VM|UMA_ZONE_NOFREE);
}

void
vm_object_clear_flag(vm_object_t object, u_short bits)
{

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        object->flags &= ~bits;
}

/*
 *      Sets the default memory attribute for the specified object.  Pages
 *      that are allocated to this object are by default assigned this memory
 *      attribute.
 *
 *      Presently, this function must be called before any pages are allocated
 *      to the object.  In the future, this requirement may be relaxed for
 *      "default" and "swap" objects.
 */
int
vm_object_set_memattr(vm_object_t object, vm_memattr_t memattr)
{

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        switch (object->type) {
        case OBJT_DEFAULT:
        case OBJT_DEVICE:
        case OBJT_PHYS:
        case OBJT_SG:
        case OBJT_SWAP:
        case OBJT_VNODE:
                if (!TAILQ_EMPTY(&object->memq))
                        return (KERN_FAILURE);
                break;
        case OBJT_DEAD:
                return (KERN_INVALID_ARGUMENT);
        }
        object->memattr = memattr;
        return (KERN_SUCCESS);
}

void
vm_object_pip_add(vm_object_t object, short i)
{

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        object->paging_in_progress += i;
}

void
vm_object_pip_subtract(vm_object_t object, short i)
{

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        object->paging_in_progress -= i;
}

void
vm_object_pip_wakeup(vm_object_t object)
{

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        object->paging_in_progress--;
        if ((object->flags & OBJ_PIPWNT) && object->paging_in_progress == 0) {
                vm_object_clear_flag(object, OBJ_PIPWNT);
                wakeup(object);
        }
}

void
vm_object_pip_wakeupn(vm_object_t object, short i)
{

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        if (i)
                object->paging_in_progress -= i;
        if ((object->flags & OBJ_PIPWNT) && object->paging_in_progress == 0) {
                vm_object_clear_flag(object, OBJ_PIPWNT);
                wakeup(object);
        }
}

void
vm_object_pip_wait(vm_object_t object, char *waitid)
{

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        while (object->paging_in_progress) {
                object->flags |= OBJ_PIPWNT;
                msleep(object, VM_OBJECT_MTX(object), PVM, waitid, 0);
        }
}

/*
 *      vm_object_allocate:
 *
 *      Returns a new object with the given size.
 */
vm_object_t
vm_object_allocate(objtype_t type, vm_pindex_t size)
{
        vm_object_t object;

        object = (vm_object_t)uma_zalloc(obj_zone, M_WAITOK);
        _vm_object_allocate(type, size, object);
        return (object);
}


/*
 *      vm_object_reference:
 *
 *      Gets another reference to the given object.  Note: OBJ_DEAD
 *      objects can be referenced during final cleaning.
 */
void
vm_object_reference(vm_object_t object)
{
        if (object == NULL)
                return;
        VM_OBJECT_LOCK(object);
        vm_object_reference_locked(object);
        VM_OBJECT_UNLOCK(object);
}

/*
 *      vm_object_reference_locked:
 *
 *      Gets another reference to the given object.
 *
 *      The object must be locked.
 */
void
vm_object_reference_locked(vm_object_t object)
{
        struct vnode *vp;

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        object->ref_count++;
        if (object->type == OBJT_VNODE) {
                vp = object->handle;
                vref(vp);
        }
}

/*
 * Handle deallocating an object of type OBJT_VNODE.
 */
static void
vm_object_vndeallocate(vm_object_t object)
{
        struct vnode *vp = (struct vnode *) object->handle;

        VFS_ASSERT_GIANT(vp->v_mount);
        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        KASSERT(object->type == OBJT_VNODE,
            ("vm_object_vndeallocate: not a vnode object"));
        KASSERT(vp != NULL, ("vm_object_vndeallocate: missing vp"));
#ifdef INVARIANTS
        if (object->ref_count == 0) {
                vprint("vm_object_vndeallocate", vp);
                panic("vm_object_vndeallocate: bad object reference count");
        }
#endif

        object->ref_count--;
        if (object->ref_count == 0) {
                mp_fixme("Unlocked vflag access.");
                vp->v_vflag &= ~VV_TEXT;
        }
        VM_OBJECT_UNLOCK(object);
        /*
         * vrele may need a vop lock
         */
        vrele(vp);
}

/*
 *      vm_object_deallocate:
 *
 *      Release a reference to the specified object,
 *      gained either through a vm_object_allocate
 *      or a vm_object_reference call.  When all references
 *      are gone, storage associated with this object
 *      may be relinquished.
 *
 *      No object may be locked.
 */
void
vm_object_deallocate(vm_object_t object)
{
        vm_object_t temp;

        while (object != NULL) {
                int vfslocked;

                vfslocked = 0;
        restart:
                VM_OBJECT_LOCK(object);
                if (object->type == OBJT_VNODE) {
                        struct vnode *vp = (struct vnode *) object->handle;

                        /*
                         * Conditionally acquire Giant for a vnode-backed
                         * object.  We have to be careful since the type of
                         * a vnode object can change while the object is
                         * unlocked.
                         */
                        if (VFS_NEEDSGIANT(vp->v_mount) && !vfslocked) {
                                vfslocked = 1;
                                if (!mtx_trylock(&Giant)) {
                                        VM_OBJECT_UNLOCK(object);
                                        mtx_lock(&Giant);
                                        goto restart;
                                }
                        }
                        vm_object_vndeallocate(object);
                        VFS_UNLOCK_GIANT(vfslocked);
                        return;
                } else
                        /*
                         * This is to handle the case that the object
                         * changed type while we dropped its lock to
                         * obtain Giant.
                         */
                        VFS_UNLOCK_GIANT(vfslocked);

                KASSERT(object->ref_count != 0,
                        ("vm_object_deallocate: object deallocated too many times: %d", object->type));

                /*
                 * If the reference count goes to 0 we start calling
                 * vm_object_terminate() on the object chain.
                 * A ref count of 1 may be a special case depending on the
                 * shadow count being 0 or 1.
                 */
                object->ref_count--;
                if (object->ref_count > 1) {
                        VM_OBJECT_UNLOCK(object);
                        return;
                } else if (object->ref_count == 1) {
                        if (object->shadow_count == 0 &&
                            object->handle == NULL &&
                            (object->type == OBJT_DEFAULT ||
                             object->type == OBJT_SWAP)) {
                                vm_object_set_flag(object, OBJ_ONEMAPPING);
                        } else if ((object->shadow_count == 1) &&
                            (object->handle == NULL) &&
                            (object->type == OBJT_DEFAULT ||
                             object->type == OBJT_SWAP)) {
                                vm_object_t robject;

                                robject = LIST_FIRST(&object->shadow_head);
                                KASSERT(robject != NULL,
                                    ("vm_object_deallocate: ref_count: %d, shadow_count: %d",
                                         object->ref_count,
                                         object->shadow_count));
                                if (!VM_OBJECT_TRYLOCK(robject)) {
                                        /*
                                         * Avoid a potential deadlock.
                                         */
                                        object->ref_count++;
                                        VM_OBJECT_UNLOCK(object);
                                        /*
                                         * More likely than not the thread
                                         * holding robject's lock has lower
                                         * priority than the current thread.
                                         * Let the lower priority thread run.
                                         */
                                        pause("vmo_de", 1);
                                        continue;
                                }
                                /*
                                 * Collapse object into its shadow unless its
                                 * shadow is dead.  In that case, object will
                                 * be deallocated by the thread that is
                                 * deallocating its shadow.
                                 */
                                if ((robject->flags & OBJ_DEAD) == 0 &&
                                    (robject->handle == NULL) &&
                                    (robject->type == OBJT_DEFAULT ||
                                     robject->type == OBJT_SWAP)) {

                                        robject->ref_count++;
retry:
                                        if (robject->paging_in_progress) {
                                                VM_OBJECT_UNLOCK(object);
                                                vm_object_pip_wait(robject,
                                                    "objde1");
                                                temp = robject->backing_object;
                                                if (object == temp) {
                                                        VM_OBJECT_LOCK(object);
                                                        goto retry;
                                                }
                                        } else if (object->paging_in_progress) {
                                                VM_OBJECT_UNLOCK(robject);
                                                object->flags |= OBJ_PIPWNT;
                                                msleep(object,
                                                    VM_OBJECT_MTX(object),
                                                    PDROP | PVM, "objde2", 0);
                                                VM_OBJECT_LOCK(robject);
                                                temp = robject->backing_object;
                                                if (object == temp) {
                                                        VM_OBJECT_LOCK(object);
                                                        goto retry;
                                                }
                                        } else
                                                VM_OBJECT_UNLOCK(object);

                                        if (robject->ref_count == 1) {
                                                robject->ref_count--;
                                                object = robject;
                                                goto doterm;
                                        }
                                        object = robject;
                                        vm_object_collapse(object);
                                        VM_OBJECT_UNLOCK(object);
                                        continue;
                                }
                                VM_OBJECT_UNLOCK(robject);
                        }
                        VM_OBJECT_UNLOCK(object);
                        return;
                }
doterm:
                temp = object->backing_object;
                if (temp != NULL) {
                        VM_OBJECT_LOCK(temp);
                        LIST_REMOVE(object, shadow_list);
                        temp->shadow_count--;
                        VM_OBJECT_UNLOCK(temp);
                        object->backing_object = NULL;
                }
                /*
                 * Don't double-terminate, we could be in a termination
                 * recursion due to the terminate having to sync data
                 * to disk.
                 */
                if ((object->flags & OBJ_DEAD) == 0)
                        vm_object_terminate(object);
                else
                        VM_OBJECT_UNLOCK(object);
                object = temp;
        }
}

/*
 *      vm_object_destroy removes the object from the global object list
 *      and frees the space for the object.
 */
void
vm_object_destroy(vm_object_t object)
{

        /*
         * Remove the object from the global object list.
         */
        mtx_lock(&vm_object_list_mtx);
        TAILQ_REMOVE(&vm_object_list, object, object_list);
        mtx_unlock(&vm_object_list_mtx);

        /*
         * Release the allocation charge.
         */
        if (object->uip != NULL) {
                KASSERT(object->type == OBJT_DEFAULT ||
                    object->type == OBJT_SWAP,
                    ("vm_object_terminate: non-swap obj %p has uip",
                     object));
                swap_release_by_uid(object->charge, object->uip);
                object->charge = 0;
                uifree(object->uip);
                object->uip = NULL;
        }

        /*
         * Free the space for the object.
         */
        uma_zfree(obj_zone, object);
}

/*
 *      vm_object_terminate actually destroys the specified object, freeing
 *      up all previously used resources.
 *
 *      The object must be locked.
 *      This routine may block.
 */
void
vm_object_terminate(vm_object_t object)
{
        vm_page_t p;

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);

        /*
         * Make sure no one uses us.
         */
        vm_object_set_flag(object, OBJ_DEAD);

        /*
         * wait for the pageout daemon to be done with the object
         */
        vm_object_pip_wait(object, "objtrm");

        KASSERT(!object->paging_in_progress,
                ("vm_object_terminate: pageout in progress"));

        /*
         * Clean and free the pages, as appropriate. All references to the
         * object are gone, so we don't need to lock it.
         */
        if (object->type == OBJT_VNODE) {
                struct vnode *vp = (struct vnode *)object->handle;

                /*
                 * Clean pages and flush buffers.
                 */
                vm_object_page_clean(object, 0, 0, OBJPC_SYNC);
                VM_OBJECT_UNLOCK(object);

                vinvalbuf(vp, V_SAVE, 0, 0);

                VM_OBJECT_LOCK(object);
        }

        KASSERT(object->ref_count == 0, 
                ("vm_object_terminate: object with references, ref_count=%d",
                object->ref_count));

        /*
         * Now free any remaining pages. For internal objects, this also
         * removes them from paging queues. Don't free wired pages, just
         * remove them from the object. 
         */
        vm_page_lock_queues();
        while ((p = TAILQ_FIRST(&object->memq)) != NULL) {
                KASSERT(!p->busy && (p->oflags & VPO_BUSY) == 0,
                        ("vm_object_terminate: freeing busy page %p "
                        "p->busy = %d, p->oflags %x\n", p, p->busy, p->oflags));
                if (p->wire_count == 0) {
                        vm_page_free(p);
                        cnt.v_pfree++;
                } else {
                        vm_page_remove(p);
                }
        }
        vm_page_unlock_queues();

#if VM_NRESERVLEVEL > 0
        if (__predict_false(!LIST_EMPTY(&object->rvq)))
                vm_reserv_break_all(object);
#endif
        if (__predict_false(object->cache != NULL))
                vm_page_cache_free(object, 0, 0);

        /*
         * Let the pager know object is dead.
         */
        vm_pager_deallocate(object);
        VM_OBJECT_UNLOCK(object);

        vm_object_destroy(object);
}

/*
 *      vm_object_page_clean
 *
 *      Clean all dirty pages in the specified range of object.  Leaves page 
 *      on whatever queue it is currently on.   If NOSYNC is set then do not
 *      write out pages with VPO_NOSYNC set (originally comes from MAP_NOSYNC),
 *      leaving the object dirty.
 *
 *      When stuffing pages asynchronously, allow clustering.  XXX we need a
 *      synchronous clustering mode implementation.
 *
 *      Odd semantics: if start == end, we clean everything.
 *
 *      The object must be locked.
 */
void
vm_object_page_clean(vm_object_t object, vm_pindex_t start, vm_pindex_t end,
    int flags)
{
        vm_page_t np, p;
        vm_pindex_t pi, tend;
        int clearobjflags, curgeneration, n, pagerflags;

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        KASSERT(object->type == OBJT_VNODE, ("Not a vnode object"));
        if ((object->flags & OBJ_MIGHTBEDIRTY) == 0 ||
            object->resident_page_count == 0)
                return;

        pagerflags = (flags & (OBJPC_SYNC | OBJPC_INVAL)) != 0 ?
            VM_PAGER_PUT_SYNC : VM_PAGER_CLUSTER_OK;
        pagerflags |= (flags & OBJPC_INVAL) != 0 ? VM_PAGER_PUT_INVAL : 0;

        tend = (end == 0) ? object->size : end;

        vm_object_set_flag(object, OBJ_CLEANING);

        vm_page_lock_queues();

        /*
         * Make the page read-only so we can then clear the object flags.
         *
         * However, if this is a nosync mmap then the object is likely to 
         * stay dirty so do not mess with the page and do not clear the
         * object flags.
         */
        clearobjflags = 1;
        for (p = vm_page_find_least(object, start);
            p != NULL && p->pindex < tend; p = TAILQ_NEXT(p, listq)) {
                if ((flags & OBJPC_NOSYNC) != 0 &&
                    (p->oflags & VPO_NOSYNC) != 0)
                        clearobjflags = 0;
                else
                        pmap_remove_write(p);
        }

        if (clearobjflags && (start == 0) && (tend == object->size))
                vm_object_clear_flag(object, OBJ_MIGHTBEDIRTY);

rescan:
        curgeneration = object->generation;

        for (p = vm_page_find_least(object, start); p != NULL; p = np) {
                pi = p->pindex;
                if (pi >= tend)
                        break;
                np = TAILQ_NEXT(p, listq);
                if (p->valid == 0)
                        continue;
                if (vm_page_sleep_if_busy(p, TRUE, "vpcwai")) {
                        vm_page_lock_queues();
                        if (object->generation != curgeneration)
                                goto rescan;
                        np = vm_page_find_least(object, pi);
                        continue;
                }
                vm_page_test_dirty(p);
                if (p->dirty == 0)
                        continue;

                /*
                 * If we have been asked to skip nosync pages and this is a
                 * nosync page, skip it.  Note that the object flags were
                 * not cleared in this case so we do not have to set them.
                 */
                if ((flags & OBJPC_NOSYNC) != 0 &&
                    (p->oflags & VPO_NOSYNC) != 0)
                        continue;

                n = vm_object_page_collect_flush(object, p, pagerflags);
                if (object->generation != curgeneration)
                        goto rescan;
                np = vm_page_find_least(object, pi + n);
        }
        vm_page_unlock_queues();
#if 0
        VOP_FSYNC(vp, (pagerflags & VM_PAGER_PUT_SYNC) ? MNT_WAIT : 0);
#endif

        vm_object_clear_flag(object, OBJ_CLEANING);
}

static int
vm_object_page_collect_flush(vm_object_t object, vm_page_t p, int pagerflags)
{
        vm_page_t ma[vm_pageout_page_count], p_first, tp;
        int count, i, mreq, runlen;

        mtx_assert(&vm_page_queue_mtx, MA_OWNED);

        count = 1;
        mreq = 0;

        for (tp = p; count < vm_pageout_page_count; count++) {
                tp = vm_page_next(tp);
                if (tp == NULL || tp->busy != 0 || (tp->oflags & VPO_BUSY) != 0)
                        break;
                vm_page_test_dirty(tp);
                if (tp->dirty == 0)
                        break;
        }

        for (p_first = p; count < vm_pageout_page_count; count++) {
                tp = vm_page_prev(p_first);
                if (tp == NULL || tp->busy != 0 || (tp->oflags & VPO_BUSY) != 0)
                        break;
                vm_page_test_dirty(tp);
                if (tp->dirty == 0)
                        break;
                p_first = tp;
                mreq++;
        }

        for (tp = p_first, i = 0; i < count; tp = TAILQ_NEXT(tp, listq), i++)
                ma[i] = tp;

        vm_pageout_flush(ma, count, pagerflags, mreq, &runlen);
        return (runlen);
}

/*
 * Note that there is absolutely no sense in writing out
 * anonymous objects, so we track down the vnode object
 * to write out.
 * We invalidate (remove) all pages from the address space
 * for semantic correctness.
 *
 * Note: certain anonymous maps, such as MAP_NOSYNC maps,
 * may start out with a NULL object.
 */
void
vm_object_sync(vm_object_t object, vm_ooffset_t offset, vm_size_t size,
    boolean_t syncio, boolean_t invalidate)
{
        vm_object_t backing_object;
        struct vnode *vp;
        struct mount *mp;
        int flags;

        if (object == NULL)
                return;
        VM_OBJECT_LOCK(object);
        while ((backing_object = object->backing_object) != NULL) {
                VM_OBJECT_LOCK(backing_object);
                offset += object->backing_object_offset;
                VM_OBJECT_UNLOCK(object);
                object = backing_object;
                if (object->size < OFF_TO_IDX(offset + size))
                        size = IDX_TO_OFF(object->size) - offset;
        }
        /*
         * Flush pages if writing is allowed, invalidate them
         * if invalidation requested.  Pages undergoing I/O
         * will be ignored by vm_object_page_remove().
         *
         * We cannot lock the vnode and then wait for paging
         * to complete without deadlocking against vm_fault.
         * Instead we simply call vm_object_page_remove() and
         * allow it to block internally on a page-by-page
         * basis when it encounters pages undergoing async
         * I/O.
         */
        if (object->type == OBJT_VNODE &&
            (object->flags & OBJ_MIGHTBEDIRTY) != 0) {
                int vfslocked;
                vp = object->handle;
                VM_OBJECT_UNLOCK(object);
                (void) vn_start_write(vp, &mp, V_WAIT);
                vfslocked = VFS_LOCK_GIANT(vp->v_mount);
                vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
                flags = (syncio || invalidate) ? OBJPC_SYNC : 0;
                flags |= invalidate ? OBJPC_INVAL : 0;
                VM_OBJECT_LOCK(object);
                vm_object_page_clean(object,
                    OFF_TO_IDX(offset),
                    OFF_TO_IDX(offset + size + PAGE_MASK),
                    flags);
                VM_OBJECT_UNLOCK(object);
                VOP_UNLOCK(vp, 0);
                VFS_UNLOCK_GIANT(vfslocked);
                vn_finished_write(mp);
                VM_OBJECT_LOCK(object);
        }
        if ((object->type == OBJT_VNODE ||
             object->type == OBJT_DEVICE) && invalidate) {
                boolean_t purge;
                purge = old_msync || (object->type == OBJT_DEVICE);
                vm_object_page_remove(object,
                    OFF_TO_IDX(offset),
                    OFF_TO_IDX(offset + size + PAGE_MASK),
                    purge ? FALSE : TRUE);
        }
        VM_OBJECT_UNLOCK(object);
}

/*
 *      vm_object_madvise:
 *
 *      Implements the madvise function at the object/page level.
 *
 *      MADV_WILLNEED   (any object)
 *
 *          Activate the specified pages if they are resident.
 *
 *      MADV_DONTNEED   (any object)
 *
 *          Deactivate the specified pages if they are resident.
 *
 *      MADV_FREE       (OBJT_DEFAULT/OBJT_SWAP objects,
 *                       OBJ_ONEMAPPING only)
 *
 *          Deactivate and clean the specified pages if they are
 *          resident.  This permits the process to reuse the pages
 *          without faulting or the kernel to reclaim the pages
 *          without I/O.
 */
void
vm_object_madvise(vm_object_t object, vm_pindex_t pindex, int count, int advise)
{
        vm_pindex_t end, tpindex;
        vm_object_t backing_object, tobject;
        vm_page_t m;

        if (object == NULL)
                return;
        VM_OBJECT_LOCK(object);
        end = pindex + count;
        /*
         * Locate and adjust resident pages
         */
        for (; pindex < end; pindex += 1) {
relookup:
                tobject = object;
                tpindex = pindex;
shadowlookup:
                /*
                 * MADV_FREE only operates on OBJT_DEFAULT or OBJT_SWAP pages
                 * and those pages must be OBJ_ONEMAPPING.
                 */
                if (advise == MADV_FREE) {
                        if ((tobject->type != OBJT_DEFAULT &&
                             tobject->type != OBJT_SWAP) ||
                            (tobject->flags & OBJ_ONEMAPPING) == 0) {
                                goto unlock_tobject;
                        }
                } else if (tobject->type == OBJT_PHYS)
                        goto unlock_tobject;
                m = vm_page_lookup(tobject, tpindex);
                if (m == NULL && advise == MADV_WILLNEED) {
                        /*
                         * If the page is cached, reactivate it.
                         */
                        m = vm_page_alloc(tobject, tpindex, VM_ALLOC_IFCACHED |
                            VM_ALLOC_NOBUSY);
                }
                if (m == NULL) {
                        /*
                         * There may be swap even if there is no backing page
                         */
                        if (advise == MADV_FREE && tobject->type == OBJT_SWAP)
                                swap_pager_freespace(tobject, tpindex, 1);
                        /*
                         * next object
                         */
                        backing_object = tobject->backing_object;
                        if (backing_object == NULL)
                                goto unlock_tobject;
                        VM_OBJECT_LOCK(backing_object);
                        tpindex += OFF_TO_IDX(tobject->backing_object_offset);
                        if (tobject != object)
                                VM_OBJECT_UNLOCK(tobject);
                        tobject = backing_object;
                        goto shadowlookup;
                } else if (m->valid != VM_PAGE_BITS_ALL)
                        goto unlock_tobject;
                /*
                 * If the page is not in a normal state, skip it.
                 */
                vm_page_lock_queues();
                if (m->hold_count != 0 || m->wire_count != 0) {
                        vm_page_unlock_queues();
                        goto unlock_tobject;
                }
                if ((m->oflags & VPO_BUSY) || m->busy) {
                        if (advise == MADV_WILLNEED)
                                /*
                                 * Reference the page before unlocking and
                                 * sleeping so that the page daemon is less
                                 * likely to reclaim it. 
                                 */
                                vm_page_flag_set(m, PG_REFERENCED);
                        vm_page_unlock_queues();
                        if (object != tobject)
                                VM_OBJECT_UNLOCK(object);
                        m->oflags |= VPO_WANTED;
                        msleep(m, VM_OBJECT_MTX(tobject), PDROP | PVM, "madvpo",
                            0);
                        VM_OBJECT_LOCK(object);
                        goto relookup;
                }
                if (advise == MADV_WILLNEED) {
                        vm_page_activate(m);
                } else if (advise == MADV_DONTNEED) {
                        vm_page_dontneed(m);
                } else if (advise == MADV_FREE) {
                        /*
                         * Mark the page clean.  This will allow the page
                         * to be freed up by the system.  However, such pages
                         * are often reused quickly by malloc()/free()
                         * so we do not do anything that would cause
                         * a page fault if we can help it.
                         *
                         * Specifically, we do not try to actually free
                         * the page now nor do we try to put it in the
                         * cache (which would cause a page fault on reuse).
                         *
                         * But we do make the page is freeable as we
                         * can without actually taking the step of unmapping
                         * it.
                         */
                        pmap_clear_modify(m);
                        m->dirty = 0;
                        m->act_count = 0;
                        vm_page_dontneed(m);
                }
                vm_page_unlock_queues();
                if (advise == MADV_FREE && tobject->type == OBJT_SWAP)
                        swap_pager_freespace(tobject, tpindex, 1);
unlock_tobject:
                if (tobject != object)
                        VM_OBJECT_UNLOCK(tobject);
        }       
        VM_OBJECT_UNLOCK(object);
}

/*
 *      vm_object_shadow:
 *
 *      Create a new object which is backed by the
 *      specified existing object range.  The source
 *      object reference is deallocated.
 *
 *      The new object and offset into that object
 *      are returned in the source parameters.
 */
void
vm_object_shadow(
        vm_object_t *object,    /* IN/OUT */
        vm_ooffset_t *offset,   /* IN/OUT */
        vm_size_t length)
{
        vm_object_t source;
        vm_object_t result;

        source = *object;

        /*
         * Don't create the new object if the old object isn't shared.
         */
        if (source != NULL) {
                VM_OBJECT_LOCK(source);
                if (source->ref_count == 1 &&
                    source->handle == NULL &&
                    (source->type == OBJT_DEFAULT ||
                     source->type == OBJT_SWAP)) {
                        VM_OBJECT_UNLOCK(source);
                        return;
                }
                VM_OBJECT_UNLOCK(source);
        }

        /*
         * Allocate a new object with the given length.
         */
        result = vm_object_allocate(OBJT_DEFAULT, length);

        /*
         * The new object shadows the source object, adding a reference to it.
         * Our caller changes his reference to point to the new object,
         * removing a reference to the source object.  Net result: no change
         * of reference count.
         *
         * Try to optimize the result object's page color when shadowing
         * in order to maintain page coloring consistency in the combined 
         * shadowed object.
         */
        result->backing_object = source;
        /*
         * Store the offset into the source object, and fix up the offset into
         * the new object.
         */
        result->backing_object_offset = *offset;
        if (source != NULL) {
                VM_OBJECT_LOCK(source);
                LIST_INSERT_HEAD(&source->shadow_head, result, shadow_list);
                source->shadow_count++;
#if VM_NRESERVLEVEL > 0
                result->flags |= source->flags & OBJ_COLORED;
                result->pg_color = (source->pg_color + OFF_TO_IDX(*offset)) &
                    ((1 << (VM_NFREEORDER - 1)) - 1);
#endif
                VM_OBJECT_UNLOCK(source);
        }


        /*
         * Return the new things
         */
        *offset = 0;
        *object = result;
}

/*
 *      vm_object_split:
 *
 * Split the pages in a map entry into a new object.  This affords
 * easier removal of unused pages, and keeps object inheritance from
 * being a negative impact on memory usage.
 */
void
vm_object_split(vm_map_entry_t entry)
{
        vm_page_t m, m_next;
        vm_object_t orig_object, new_object, source;
        vm_pindex_t idx, offidxstart;
        vm_size_t size;

        orig_object = entry->object.vm_object;
        if (orig_object->type != OBJT_DEFAULT && orig_object->type != OBJT_SWAP)
                return;
        if (orig_object->ref_count <= 1)
                return;
        VM_OBJECT_UNLOCK(orig_object);

        offidxstart = OFF_TO_IDX(entry->offset);
        size = atop(entry->end - entry->start);

        /*
         * If swap_pager_copy() is later called, it will convert new_object
         * into a swap object.
         */
        new_object = vm_object_allocate(OBJT_DEFAULT, size);

        /*
         * At this point, the new object is still private, so the order in
         * which the original and new objects are locked does not matter.
         */
        VM_OBJECT_LOCK(new_object);
        VM_OBJECT_LOCK(orig_object);
        source = orig_object->backing_object;
        if (source != NULL) {
                VM_OBJECT_LOCK(source);
                if ((source->flags & OBJ_DEAD) != 0) {
                        VM_OBJECT_UNLOCK(source);
                        VM_OBJECT_UNLOCK(orig_object);
                        VM_OBJECT_UNLOCK(new_object);
                        vm_object_deallocate(new_object);
                        VM_OBJECT_LOCK(orig_object);
                        return;
                }
                LIST_INSERT_HEAD(&source->shadow_head,
                                  new_object, shadow_list);
                source->shadow_count++;
                vm_object_reference_locked(source);     /* for new_object */
                vm_object_clear_flag(source, OBJ_ONEMAPPING);
                VM_OBJECT_UNLOCK(source);
                new_object->backing_object_offset = 
                        orig_object->backing_object_offset + entry->offset;
                new_object->backing_object = source;
        }
        if (orig_object->uip != NULL) {
                new_object->uip = orig_object->uip;
                uihold(orig_object->uip);
                new_object->charge = ptoa(size);
                KASSERT(orig_object->charge >= ptoa(size),
                    ("orig_object->charge < 0"));
                orig_object->charge -= ptoa(size);
        }
retry:
        m = vm_page_find_least(orig_object, offidxstart);
        vm_page_lock_queues();
        for (; m != NULL && (idx = m->pindex - offidxstart) < size;
            m = m_next) {
                m_next = TAILQ_NEXT(m, listq);

                /*
                 * We must wait for pending I/O to complete before we can
                 * rename the page.
                 *
                 * We do not have to VM_PROT_NONE the page as mappings should
                 * not be changed by this operation.
                 */
                if ((m->oflags & VPO_BUSY) || m->busy) {
                        vm_page_unlock_queues();
                        VM_OBJECT_UNLOCK(new_object);
                        m->oflags |= VPO_WANTED;
                        msleep(m, VM_OBJECT_MTX(orig_object), PVM, "spltwt", 0);
                        VM_OBJECT_LOCK(new_object);
                        goto retry;
                }
                vm_page_rename(m, new_object, idx);
                /* page automatically made dirty by rename and cache handled */
                vm_page_busy(m);
        }
        vm_page_unlock_queues();
        if (orig_object->type == OBJT_SWAP) {
                /*
                 * swap_pager_copy() can sleep, in which case the orig_object's
                 * and new_object's locks are released and reacquired. 
                 */
                swap_pager_copy(orig_object, new_object, offidxstart, 0);

                /*
                 * Transfer any cached pages from orig_object to new_object.
                 */
                if (__predict_false(orig_object->cache != NULL))
                        vm_page_cache_transfer(orig_object, offidxstart,
                            new_object);
        }
        VM_OBJECT_UNLOCK(orig_object);
        TAILQ_FOREACH(m, &new_object->memq, listq)
                vm_page_wakeup(m);
        VM_OBJECT_UNLOCK(new_object);
        entry->object.vm_object = new_object;
        entry->offset = 0LL;
        vm_object_deallocate(orig_object);
        VM_OBJECT_LOCK(new_object);
}

#define OBSC_TEST_ALL_SHADOWED  0x0001
#define OBSC_COLLAPSE_NOWAIT    0x0002
#define OBSC_COLLAPSE_WAIT      0x0004

static int
vm_object_backing_scan(vm_object_t object, int op)
{
        int r = 1;
        vm_page_t p;
        vm_object_t backing_object;
        vm_pindex_t backing_offset_index;

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        VM_OBJECT_LOCK_ASSERT(object->backing_object, MA_OWNED);

        backing_object = object->backing_object;
        backing_offset_index = OFF_TO_IDX(object->backing_object_offset);

        /*
         * Initial conditions
         */
        if (op & OBSC_TEST_ALL_SHADOWED) {
                /*
                 * We do not want to have to test for the existence of cache
                 * or swap pages in the backing object.  XXX but with the
                 * new swapper this would be pretty easy to do.
                 *
                 * XXX what about anonymous MAP_SHARED memory that hasn't
                 * been ZFOD faulted yet?  If we do not test for this, the
                 * shadow test may succeed! XXX
                 */
                if (backing_object->type != OBJT_DEFAULT) {
                        return (0);
                }
        }
        if (op & OBSC_COLLAPSE_WAIT) {
                vm_object_set_flag(backing_object, OBJ_DEAD);
        }

        /*
         * Our scan
         */
        p = TAILQ_FIRST(&backing_object->memq);
        while (p) {
                vm_page_t next = TAILQ_NEXT(p, listq);
                vm_pindex_t new_pindex = p->pindex - backing_offset_index;

                if (op & OBSC_TEST_ALL_SHADOWED) {
                        vm_page_t pp;

                        /*
                         * Ignore pages outside the parent object's range
                         * and outside the parent object's mapping of the 
                         * backing object.
                         *
                         * note that we do not busy the backing object's
                         * page.
                         */
                        if (
                            p->pindex < backing_offset_index ||
                            new_pindex >= object->size
                        ) {
                                p = next;
                                continue;
                        }

                        /*
                         * See if the parent has the page or if the parent's
                         * object pager has the page.  If the parent has the
                         * page but the page is not valid, the parent's
                         * object pager must have the page.
                         *
                         * If this fails, the parent does not completely shadow
                         * the object and we might as well give up now.
                         */

                        pp = vm_page_lookup(object, new_pindex);
                        if (
                            (pp == NULL || pp->valid == 0) &&
                            !vm_pager_has_page(object, new_pindex, NULL, NULL)
                        ) {
                                r = 0;
                                break;
                        }
                }

                /*
                 * Check for busy page
                 */
                if (op & (OBSC_COLLAPSE_WAIT | OBSC_COLLAPSE_NOWAIT)) {
                        vm_page_t pp;

                        if (op & OBSC_COLLAPSE_NOWAIT) {
                                if ((p->oflags & VPO_BUSY) ||
                                    !p->valid || 
                                    p->busy) {
                                        p = next;
                                        continue;
                                }
                        } else if (op & OBSC_COLLAPSE_WAIT) {
                                if ((p->oflags & VPO_BUSY) || p->busy) {
                                        VM_OBJECT_UNLOCK(object);
                                        p->oflags |= VPO_WANTED;
                                        msleep(p, VM_OBJECT_MTX(backing_object),
                                            PDROP | PVM, "vmocol", 0);
                                        VM_OBJECT_LOCK(object);
                                        VM_OBJECT_LOCK(backing_object);
                                        /*
                                         * If we slept, anything could have
                                         * happened.  Since the object is
                                         * marked dead, the backing offset
                                         * should not have changed so we
                                         * just restart our scan.
                                         */
                                        p = TAILQ_FIRST(&backing_object->memq);
                                        continue;
                                }
                        }

                        KASSERT(
                            p->object == backing_object,
                            ("vm_object_backing_scan: object mismatch")
                        );

                        /*
                         * Destroy any associated swap
                         */
                        if (backing_object->type == OBJT_SWAP) {
                                swap_pager_freespace(
                                    backing_object, 
                                    p->pindex,
                                    1
                                );
                        }

                        if (
                            p->pindex < backing_offset_index ||
                            new_pindex >= object->size
                        ) {
                                /*
                                 * Page is out of the parent object's range, we 
                                 * can simply destroy it. 
                                 */
                                vm_page_lock_queues();
                                KASSERT(!pmap_page_is_mapped(p),
                                    ("freeing mapped page %p", p));
                                if (p->wire_count == 0)
                                        vm_page_free(p);
                                else
                                        vm_page_remove(p);
                                vm_page_unlock_queues();
                                p = next;
                                continue;
                        }

                        pp = vm_page_lookup(object, new_pindex);
                        if (
                            pp != NULL ||
                            vm_pager_has_page(object, new_pindex, NULL, NULL)
                        ) {
                                /*
                                 * page already exists in parent OR swap exists
                                 * for this location in the parent.  Destroy 
                                 * the original page from the backing object.
                                 *
                                 * Leave the parent's page alone
                                 */
                                vm_page_lock_queues();
                                KASSERT(!pmap_page_is_mapped(p),
                                    ("freeing mapped page %p", p));
                                if (p->wire_count == 0)
                                        vm_page_free(p);
                                else
                                        vm_page_remove(p);
                                vm_page_unlock_queues();
                                p = next;
                                continue;
                        }

#if VM_NRESERVLEVEL > 0
                        /*
                         * Rename the reservation.
                         */
                        vm_reserv_rename(p, object, backing_object,
                            backing_offset_index);
#endif

                        /*
                         * Page does not exist in parent, rename the
                         * page from the backing object to the main object. 
                         *
                         * If the page was mapped to a process, it can remain 
                         * mapped through the rename.
                         */
                        vm_page_lock_queues();
                        vm_page_rename(p, object, new_pindex);
                        vm_page_unlock_queues();
                        /* page automatically made dirty by rename */
                }
                p = next;
        }
        return (r);
}


/*
 * this version of collapse allows the operation to occur earlier and
 * when paging_in_progress is true for an object...  This is not a complete
 * operation, but should plug 99.9% of the rest of the leaks.
 */
static void
vm_object_qcollapse(vm_object_t object)
{
        vm_object_t backing_object = object->backing_object;

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        VM_OBJECT_LOCK_ASSERT(backing_object, MA_OWNED);

        if (backing_object->ref_count != 1)
                return;

        vm_object_backing_scan(object, OBSC_COLLAPSE_NOWAIT);
}

/*
 *      vm_object_collapse:
 *
 *      Collapse an object with the object backing it.
 *      Pages in the backing object are moved into the
 *      parent, and the backing object is deallocated.
 */
void
vm_object_collapse(vm_object_t object)
{
        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        
        while (TRUE) {
                vm_object_t backing_object;

                /*
                 * Verify that the conditions are right for collapse:
                 *
                 * The object exists and the backing object exists.
                 */
                if ((backing_object = object->backing_object) == NULL)
                        break;

                /*
                 * we check the backing object first, because it is most likely
                 * not collapsable.
                 */
                VM_OBJECT_LOCK(backing_object);
                if (backing_object->handle != NULL ||
                    (backing_object->type != OBJT_DEFAULT &&
                     backing_object->type != OBJT_SWAP) ||
                    (backing_object->flags & OBJ_DEAD) ||
                    object->handle != NULL ||
                    (object->type != OBJT_DEFAULT &&
                     object->type != OBJT_SWAP) ||
                    (object->flags & OBJ_DEAD)) {
                        VM_OBJECT_UNLOCK(backing_object);
                        break;
                }

                if (
                    object->paging_in_progress != 0 ||
                    backing_object->paging_in_progress != 0
                ) {
                        vm_object_qcollapse(object);
                        VM_OBJECT_UNLOCK(backing_object);
                        break;
                }
                /*
                 * We know that we can either collapse the backing object (if
                 * the parent is the only reference to it) or (perhaps) have
                 * the parent bypass the object if the parent happens to shadow
                 * all the resident pages in the entire backing object.
                 *
                 * This is ignoring pager-backed pages such as swap pages.
                 * vm_object_backing_scan fails the shadowing test in this
                 * case.
                 */
                if (backing_object->ref_count == 1) {
                        /*
                         * If there is exactly one reference to the backing
                         * object, we can collapse it into the parent.  
                         */
                        vm_object_backing_scan(object, OBSC_COLLAPSE_WAIT);

#if VM_NRESERVLEVEL > 0
                        /*
                         * Break any reservations from backing_object.
                         */
                        if (__predict_false(!LIST_EMPTY(&backing_object->rvq)))
                                vm_reserv_break_all(backing_object);
#endif

                        /*
                         * Move the pager from backing_object to object.
                         */
                        if (backing_object->type == OBJT_SWAP) {
                                /*
                                 * swap_pager_copy() can sleep, in which case
                                 * the backing_object's and object's locks are
                                 * released and reacquired.
                                 */
                                swap_pager_copy(
                                    backing_object,
                                    object,
                                    OFF_TO_IDX(object->backing_object_offset), TRUE);

                                /*
                                 * Free any cached pages from backing_object.
                                 */
                                if (__predict_false(backing_object->cache != NULL))
                                        vm_page_cache_free(backing_object, 0, 0);
                        }
                        /*
                         * Object now shadows whatever backing_object did.
                         * Note that the reference to 
                         * backing_object->backing_object moves from within 
                         * backing_object to within object.
                         */
                        LIST_REMOVE(object, shadow_list);
                        backing_object->shadow_count--;
                        if (backing_object->backing_object) {
                                VM_OBJECT_LOCK(backing_object->backing_object);
                                LIST_REMOVE(backing_object, shadow_list);
                                LIST_INSERT_HEAD(
                                    &backing_object->backing_object->shadow_head,
                                    object, shadow_list);
                                /*
                                 * The shadow_count has not changed.
                                 */
                                VM_OBJECT_UNLOCK(backing_object->backing_object);
                        }
                        object->backing_object = backing_object->backing_object;
                        object->backing_object_offset +=
                            backing_object->backing_object_offset;

                        /*
                         * Discard backing_object.
                         *
                         * Since the backing object has no pages, no pager left,
                         * and no object references within it, all that is
                         * necessary is to dispose of it.
                         */
                        KASSERT(backing_object->ref_count == 1, (
"backing_object %p was somehow re-referenced during collapse!",
                            backing_object));
                        VM_OBJECT_UNLOCK(backing_object);
                        vm_object_destroy(backing_object);

                        object_collapses++;
                } else {
                        vm_object_t new_backing_object;

                        /*
                         * If we do not entirely shadow the backing object,
                         * there is nothing we can do so we give up.
                         */
                        if (object->resident_page_count != object->size &&
                            vm_object_backing_scan(object,
                            OBSC_TEST_ALL_SHADOWED) == 0) {
                                VM_OBJECT_UNLOCK(backing_object);
                                break;
                        }

                        /*
                         * Make the parent shadow the next object in the
                         * chain.  Deallocating backing_object will not remove
                         * it, since its reference count is at least 2.
                         */
                        LIST_REMOVE(object, shadow_list);
                        backing_object->shadow_count--;

                        new_backing_object = backing_object->backing_object;
                        if ((object->backing_object = new_backing_object) != NULL) {
                                VM_OBJECT_LOCK(new_backing_object);
                                LIST_INSERT_HEAD(
                                    &new_backing_object->shadow_head,
                                    object,
                                    shadow_list
                                );
                                new_backing_object->shadow_count++;
                                vm_object_reference_locked(new_backing_object);
                                VM_OBJECT_UNLOCK(new_backing_object);
                                object->backing_object_offset +=
                                        backing_object->backing_object_offset;
                        }

                        /*
                         * Drop the reference count on backing_object. Since
                         * its ref_count was at least 2, it will not vanish.
                         */
                        backing_object->ref_count--;
                        VM_OBJECT_UNLOCK(backing_object);
                        object_bypasses++;
                }

                /*
                 * Try again with this object's new backing object.
                 */
        }
}

/*
 *      vm_object_page_remove:
 *
 *      For the given object, either frees or invalidates each of the
 *      specified pages.  In general, a page is freed.  However, if a
 *      page is wired for any reason other than the existence of a
 *      managed, wired mapping, then it may be invalidated but not
 *      removed from the object.  Pages are specified by the given
 *      range ["start", "end") and Boolean "clean_only".  As a
 *      special case, if "end" is zero, then the range extends from
 *      "start" to the end of the object.  If "clean_only" is TRUE,
 *      then only the non-dirty pages within the specified range are
 *      affected.
 *
 *      In general, this operation should only be performed on objects
 *      that contain managed pages.  There are two exceptions.  First,
 *      it may be performed on the kernel and kmem objects.  Second,
 *      it may be used by msync(..., MS_INVALIDATE) to invalidate
 *      device-backed pages.  In both of these cases, "clean_only"
 *      must be FALSE.
 *
 *      The object must be locked.
 */
void
vm_object_page_remove(vm_object_t object, vm_pindex_t start, vm_pindex_t end,
    boolean_t clean_only)
{
        vm_page_t p, next;
        int wirings;

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        if (object->resident_page_count == 0)
                goto skipmemq;

        /*
         * Since physically-backed objects do not use managed pages, we can't
         * remove pages from the object (we must instead remove the page
         * references, and then destroy the object).
         */
        KASSERT(object->type != OBJT_PHYS || object == kernel_object ||
            object == kmem_object,
            ("attempt to remove pages from a physical object"));

        vm_object_pip_add(object, 1);
again:
        p = vm_page_find_least(object, start);
        vm_page_lock_queues();
        /*
         * Assert: the variable p is either (1) the page with the
         * least pindex greater than or equal to the parameter pindex
         * or (2) NULL.
         */
        for (;
             p != NULL && (p->pindex < end || end == 0);
             p = next) {
                next = TAILQ_NEXT(p, listq);

                /*
                 * If the page is wired for any reason besides the
                 * existence of managed, wired mappings, then it cannot
                 * be freed.  For example, fictitious pages, which
                 * represent device memory, are inherently wired and
                 * cannot be freed.  They can, however, be invalidated
                 * if "clean_only" is FALSE.
                 */
                if ((wirings = p->wire_count) != 0 &&
                    (wirings = pmap_page_wired_mappings(p)) != p->wire_count) {
                        /* Fictitious pages do not have managed mappings. */
                        if ((p->flags & PG_FICTITIOUS) == 0)
                                pmap_remove_all(p);
                        /* Account for removal of managed, wired mappings. */
                        p->wire_count -= wirings;
                        if (!clean_only) {
                                p->valid = 0;
                                vm_page_undirty(p);
                        }
                        continue;
                }
                if (vm_page_sleep_if_busy(p, TRUE, "vmopar"))
                        goto again;
                KASSERT((p->flags & PG_FICTITIOUS) == 0,
                    ("vm_object_page_remove: page %p is fictitious", p));
                if (clean_only && p->valid) {
                        pmap_remove_write(p);
                        if (p->dirty)
                                continue;
                }
                pmap_remove_all(p);
                /* Account for removal of managed, wired mappings. */
                if (wirings != 0)
                        p->wire_count -= wirings;
                vm_page_free(p);
        }
        vm_page_unlock_queues();
        vm_object_pip_wakeup(object);
skipmemq:
        if (__predict_false(object->cache != NULL))
                vm_page_cache_free(object, start, end);
}

/*
 *      Populate the specified range of the object with valid pages.  Returns
 *      TRUE if the range is successfully populated and FALSE otherwise.
 *
 *      Note: This function should be optimized to pass a larger array of
 *      pages to vm_pager_get_pages() before it is applied to a non-
 *      OBJT_DEVICE object.
 *
 *      The object must be locked.
 */
boolean_t
vm_object_populate(vm_object_t object, vm_pindex_t start, vm_pindex_t end)
{
        vm_page_t m, ma[1];
        vm_pindex_t pindex;
        int rv;

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        for (pindex = start; pindex < end; pindex++) {
                m = vm_page_grab(object, pindex, VM_ALLOC_NORMAL |
                    VM_ALLOC_RETRY);
                if (m->valid != VM_PAGE_BITS_ALL) {
                        ma[0] = m;
                        rv = vm_pager_get_pages(object, ma, 1, 0);
                        m = vm_page_lookup(object, pindex);
                        if (m == NULL)
                                break;
                        if (rv != VM_PAGER_OK) {
                                vm_page_lock_queues();
                                vm_page_free(m);
                                vm_page_unlock_queues();
                                break;
                        }
                }
                /*
                 * Keep "m" busy because a subsequent iteration may unlock
                 * the object.
                 */
        }
        if (pindex > start) {
                m = vm_page_lookup(object, start);
                while (m != NULL && m->pindex < pindex) {
                        vm_page_wakeup(m);
                        m = TAILQ_NEXT(m, listq);
                }
        }
        return (pindex == end);
}

/*
 *      Routine:        vm_object_coalesce
 *      Function:       Coalesces two objects backing up adjoining
 *                      regions of memory into a single object.
 *
 *      returns TRUE if objects were combined.
 *
 *      NOTE:   Only works at the moment if the second object is NULL -
 *              if it's not, which object do we lock first?
 *
 *      Parameters:
 *              prev_object     First object to coalesce
 *              prev_offset     Offset into prev_object
 *              prev_size       Size of reference to prev_object
 *              next_size       Size of reference to the second object
 *              reserved        Indicator that extension region has
 *                              swap accounted for
 *
 *      Conditions:
 *      The object must *not* be locked.
 */
boolean_t
vm_object_coalesce(vm_object_t prev_object, vm_ooffset_t prev_offset,
    vm_size_t prev_size, vm_size_t next_size, boolean_t reserved)
{
        vm_pindex_t next_pindex;

        if (prev_object == NULL)
                return (TRUE);
        VM_OBJECT_LOCK(prev_object);
        if (prev_object->type != OBJT_DEFAULT &&
            prev_object->type != OBJT_SWAP) {
                VM_OBJECT_UNLOCK(prev_object);
                return (FALSE);
        }

        /*
         * Try to collapse the object first
         */
        vm_object_collapse(prev_object);

        /*
         * Can't coalesce if: . more than one reference . paged out . shadows
         * another object . has a copy elsewhere (any of which mean that the
         * pages not mapped to prev_entry may be in use anyway)
         */
        if (prev_object->backing_object != NULL) {
                VM_OBJECT_UNLOCK(prev_object);
                return (FALSE);
        }

        prev_size >>= PAGE_SHIFT;
        next_size >>= PAGE_SHIFT;
        next_pindex = OFF_TO_IDX(prev_offset) + prev_size;

        if ((prev_object->ref_count > 1) &&
            (prev_object->size != next_pindex)) {
                VM_OBJECT_UNLOCK(prev_object);
                return (FALSE);
        }

        /*
         * Account for the charge.
         */
        if (prev_object->uip != NULL) {

                /*
                 * If prev_object was charged, then this mapping,
                 * althought not charged now, may become writable
                 * later. Non-NULL uip in the object would prevent
                 * swap reservation during enabling of the write
                 * access, so reserve swap now. Failed reservation
                 * cause allocation of the separate object for the map
                 * entry, and swap reservation for this entry is
                 * managed in appropriate time.
                 */
                if (!reserved && !swap_reserve_by_uid(ptoa(next_size),
                    prev_object->uip)) {
                        return (FALSE);
                }
                prev_object->charge += ptoa(next_size);
        }

        /*
         * Remove any pages that may still be in the object from a previous
         * deallocation.
         */
        if (next_pindex < prev_object->size) {
                vm_object_page_remove(prev_object,
                                      next_pindex,
                                      next_pindex + next_size, FALSE);
                if (prev_object->type == OBJT_SWAP)
                        swap_pager_freespace(prev_object,
                                             next_pindex, next_size);
#if 0
                if (prev_object->uip != NULL) {
                        KASSERT(prev_object->charge >=
                            ptoa(prev_object->size - next_pindex),
                            ("object %p overcharged 1 %jx %jx", prev_object,
                                (uintmax_t)next_pindex, (uintmax_t)next_size));
                        prev_object->charge -= ptoa(prev_object->size -
                            next_pindex);
                }
#endif
        }

        /*
         * Extend the object if necessary.
         */
        if (next_pindex + next_size > prev_object->size)
                prev_object->size = next_pindex + next_size;

        VM_OBJECT_UNLOCK(prev_object);
        return (TRUE);
}

void
vm_object_set_writeable_dirty(vm_object_t object)
{

        VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
        if (object->type != OBJT_VNODE ||
            (object->flags & OBJ_MIGHTBEDIRTY) != 0)
                return;
        vm_object_set_flag(object, OBJ_MIGHTBEDIRTY);
}

#include "opt_ddb.h"
#ifdef DDB
#include <sys/kernel.h>

#include <sys/cons.h>

#include <ddb/ddb.h>

static int
_vm_object_in_map(vm_map_t map, vm_object_t object, vm_map_entry_t entry)
{
        vm_map_t tmpm;
        vm_map_entry_t tmpe;
        vm_object_t obj;
        int entcount;

        if (map == 0)
                return 0;

        if (entry == 0) {
                tmpe = map->header.next;
                entcount = map->nentries;
                while (entcount-- && (tmpe != &map->header)) {
                        if (_vm_object_in_map(map, object, tmpe)) {
                                return 1;
                        }
                        tmpe = tmpe->next;
                }
        } else if (entry->eflags & MAP_ENTRY_IS_SUB_MAP) {
                tmpm = entry->object.sub_map;
                tmpe = tmpm->header.next;
                entcount = tmpm->nentries;
                while (entcount-- && tmpe != &tmpm->header) {
                        if (_vm_object_in_map(tmpm, object, tmpe)) {
                                return 1;
                        }
                        tmpe = tmpe->next;
                }
        } else if ((obj = entry->object.vm_object) != NULL) {
                for (; obj; obj = obj->backing_object)
                        if (obj == object) {
                                return 1;
                        }
        }
        return 0;
}

static int
vm_object_in_map(vm_object_t object)
{
        struct proc *p;

        /* sx_slock(&allproc_lock); */
        FOREACH_PROC_IN_SYSTEM(p) {
                if (!p->p_vmspace /* || (p->p_flag & (P_SYSTEM|P_WEXIT)) */)
                        continue;
                if (_vm_object_in_map(&p->p_vmspace->vm_map, object, 0)) {
                        /* sx_sunlock(&allproc_lock); */
                        return 1;
                }
        }
        /* sx_sunlock(&allproc_lock); */
        if (_vm_object_in_map(kernel_map, object, 0))
                return 1;
        if (_vm_object_in_map(kmem_map, object, 0))
                return 1;
        if (_vm_object_in_map(pager_map, object, 0))
                return 1;
        if (_vm_object_in_map(buffer_map, object, 0))
                return 1;
        return 0;
}

DB_SHOW_COMMAND(vmochk, vm_object_check)
{
        vm_object_t object;

        /*
         * make sure that internal objs are in a map somewhere
         * and none have zero ref counts.
         */
        TAILQ_FOREACH(object, &vm_object_list, object_list) {
                if (object->handle == NULL &&
                    (object->type == OBJT_DEFAULT || object->type == OBJT_SWAP)) {
                        if (object->ref_count == 0) {
                                db_printf("vmochk: internal obj has zero ref count: %ld\n",
                                        (long)object->size);
                        }
                        if (!vm_object_in_map(object)) {
                                db_printf(
                        "vmochk: internal obj is not in a map: "
                        "ref: %d, size: %lu: 0x%lx, backing_object: %p\n",
                                    object->ref_count, (u_long)object->size, 
                                    (u_long)object->size,
                                    (void *)object->backing_object);
                        }
                }
        }
}

/*
 *      vm_object_print:        [ debug ]
 */
DB_SHOW_COMMAND(object, vm_object_print_static)
{
        /* XXX convert args. */
        vm_object_t object = (vm_object_t)addr;
        boolean_t full = have_addr;

        vm_page_t p;

        /* XXX count is an (unused) arg.  Avoid shadowing it. */
#define count   was_count

        int count;

        if (object == NULL)
                return;

        db_iprintf(
            "Object %p: type=%d, size=0x%jx, res=%d, ref=%d, flags=0x%x uip %d charge %jx\n",
            object, (int)object->type, (uintmax_t)object->size,
            object->resident_page_count, object->ref_count, object->flags,
            object->uip ? object->uip->ui_uid : -1, (uintmax_t)object->charge);
        db_iprintf(" sref=%d, backing_object(%d)=(%p)+0x%jx\n",
            object->shadow_count, 
            object->backing_object ? object->backing_object->ref_count : 0,
            object->backing_object, (uintmax_t)object->backing_object_offset);

        if (!full)
                return;

        db_indent += 2;
        count = 0;
        TAILQ_FOREACH(p, &object->memq, listq) {
                if (count == 0)
                        db_iprintf("memory:=");
                else if (count == 6) {
                        db_printf("\n");
                        db_iprintf(" ...");
                        count = 0;
                } else
                        db_printf(",");
                count++;

                db_printf("(off=0x%jx,page=0x%jx)",
                    (uintmax_t)p->pindex, (uintmax_t)VM_PAGE_TO_PHYS(p));
        }
        if (count != 0)
                db_printf("\n");
        db_indent -= 2;
}

/* XXX. */
#undef count

/* XXX need this non-static entry for calling from vm_map_print. */
void
vm_object_print(
        /* db_expr_t */ long addr,
        boolean_t have_addr,
        /* db_expr_t */ long count,
        char *modif)
{
        vm_object_print_static(addr, have_addr, count, modif);
}

DB_SHOW_COMMAND(vmopag, vm_object_print_pages)
{
        vm_object_t object;
        vm_pindex_t fidx;
        vm_paddr_t pa;
        vm_page_t m, prev_m;
        int rcount, nl, c;

        nl = 0;
        TAILQ_FOREACH(object, &vm_object_list, object_list) {
                db_printf("new object: %p\n", (void *)object);
                if (nl > 18) {
                        c = cngetc();
                        if (c != ' ')
                                return;
                        nl = 0;
                }
                nl++;
                rcount = 0;
                fidx = 0;
                pa = -1;
                TAILQ_FOREACH(m, &object->memq, listq) {
                        if (m->pindex > 128)
                                break;
                        if ((prev_m = TAILQ_PREV(m, pglist, listq)) != NULL &&
                            prev_m->pindex + 1 != m->pindex) {
                                if (rcount) {
                                        db_printf(" index(%ld)run(%d)pa(0x%lx)\n",
                                                (long)fidx, rcount, (long)pa);
                                        if (nl > 18) {
                                                c = cngetc();
                                                if (c != ' ')
                                                        return;
                                                nl = 0;
                                        }
                                        nl++;
                                        rcount = 0;
                                }
                        }                               
                        if (rcount &&
                                (VM_PAGE_TO_PHYS(m) == pa + rcount * PAGE_SIZE)) {
                                ++rcount;
                                continue;
                        }
                        if (rcount) {
                                db_printf(" index(%ld)run(%d)pa(0x%lx)\n",
                                        (long)fidx, rcount, (long)pa);
                                if (nl > 18) {
                                        c = cngetc();
                                        if (c != ' ')
                                                return;
                                        nl = 0;
                                }
                                nl++;
                        }
                        fidx = m->pindex;
                        pa = VM_PAGE_TO_PHYS(m);
                        rcount = 1;
                }
                if (rcount) {
                        db_printf(" index(%ld)run(%d)pa(0x%lx)\n",
                                (long)fidx, rcount, (long)pa);
                        if (nl > 18) {
                                c = cngetc();
                                if (c != ' ')
                                        return;
                                nl = 0;
                        }
                        nl++;
                }
        }
}
#endif /* DDB */