Merge branch 'master' of /repository/git/dragonfly

[dragonfly.git] / sys / vm / vm_object.c

/*
 * (MPSAFE)
 *
 * 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 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.
 *
 * $FreeBSD: src/sys/vm/vm_object.c,v 1.171.2.8 2003/05/26 19:17:56 alc Exp $
 */

/*
 *      Virtual memory object module.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>           /* for curproc, pageproc */
#include <sys/thread.h>
#include <sys/vnode.h>
#include <sys/vmmeter.h>
#include <sys/mman.h>
#include <sys/mount.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/refcount.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_zone.h>

#define EASY_SCAN_FACTOR        8

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


/*
 *      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;         /* locked by vmobj_token */
struct vm_object kernel_object;

static long vm_object_count;            /* locked by vmobj_token */
extern int vm_pageout_page_count;

static long object_collapses;
static long object_bypasses;
static int next_index;
static vm_zone_t obj_zone;
static struct vm_zone obj_zone_store;
#define VM_OBJECTS_INIT 256
static struct vm_object vm_objects_init[VM_OBJECTS_INIT];

/*
 * Misc low level routines
 */
static void
vm_object_lock_init(vm_object_t obj)
{
#if defined(DEBUG_LOCKS)
        int i;

        obj->debug_hold_bitmap = 0;
        obj->debug_hold_ovfl = 0;
        for (i = 0; i < VMOBJ_DEBUG_ARRAY_SIZE; i++) {
                obj->debug_hold_thrs[i] = NULL;
                obj->debug_hold_file[i] = NULL;
                obj->debug_hold_line[i] = 0;
        }
#endif
}

static void
vm_object_lock_swap(void)
{
        lwkt_token_swap();
}

void
vm_object_lock(vm_object_t obj)
{
        lwkt_getpooltoken(obj);
}

void
vm_object_unlock(vm_object_t obj)
{
        lwkt_relpooltoken(obj);
}

static __inline void
vm_object_assert_held(vm_object_t obj)
{
        ASSERT_LWKT_TOKEN_HELD(lwkt_token_pool_lookup(obj));
}

void
#ifndef DEBUG_LOCKS
vm_object_hold(vm_object_t obj)
#else
debugvm_object_hold(vm_object_t obj, char *file, int line)
#endif
{
        if (obj == NULL)
                return;

        /*
         * Object must be held (object allocation is stable due to callers
         * context, typically already holding the token on a parent object)
         * prior to potentially blocking on the lock, otherwise the object
         * can get ripped away from us.
         */
        refcount_acquire(&obj->hold_count);
        vm_object_lock(obj);

#if defined(DEBUG_LOCKS)
        int i;

        i = ffs(~obj->debug_hold_bitmap) - 1;
        if (i == -1) {
                kprintf("vm_object hold count > VMOBJ_DEBUG_ARRAY_SIZE");
                obj->debug_hold_ovfl = 1;
        }

        obj->debug_hold_bitmap |= (1 << i);
        obj->debug_hold_thrs[i] = curthread;
        obj->debug_hold_file[i] = file;
        obj->debug_hold_line[i] = line;
#endif
}

void
vm_object_drop(vm_object_t obj)
{
        if (obj == NULL)
                return;

#if defined(DEBUG_LOCKS)
        int found = 0;
        int i;

        for (i = 0; i < VMOBJ_DEBUG_ARRAY_SIZE; i++) {
                if ((obj->debug_hold_bitmap & (1 << i)) &&
                    (obj->debug_hold_thrs[i] == curthread)) {
                        obj->debug_hold_bitmap &= ~(1 << i);
                        obj->debug_hold_thrs[i] = NULL;
                        obj->debug_hold_file[i] = NULL;
                        obj->debug_hold_line[i] = 0;
                        found = 1;
                        break;
                }
        }

        if (found == 0 && obj->debug_hold_ovfl == 0)
                panic("vm_object: attempt to drop hold on non-self-held obj");
#endif

        /*
         * The lock is a pool token, keep holding it across potential
         * wakeups to interlock the tsleep/wakeup.
         */
        if (refcount_release(&obj->hold_count))
                wakeup(obj);
        vm_object_unlock(obj);
}

/*
 * This can only be called while the caller holds the object
 * with the OBJ_DEAD interlock.  Since there are no refs this
 * is the only thing preventing an object destruction race.
 */
static void
vm_object_hold_wait(vm_object_t obj)
{
        vm_object_lock(obj);

#if defined(DEBUG_LOCKS)
        int i;

        for (i = 0; i < VMOBJ_DEBUG_ARRAY_SIZE; i++) {
                if ((obj->debug_hold_bitmap & (1 << i)) &&
                    (obj->debug_hold_thrs[i] == curthread))  {
                        kprintf("vm_object %p: self-hold in at %s:%d\n", obj,
                                obj->debug_hold_file[i], obj->debug_hold_line[i]);
                        panic("vm_object: self-hold in terminate or collapse");
                }
        }
#endif

        while (obj->hold_count)
                tsleep(obj, 0, "vmobjhld", 0);

        vm_object_unlock(obj);
}


/*
 * Initialize a freshly allocated object
 *
 * Used only by vm_object_allocate() and zinitna().
 *
 * No requirements.
 */
void
_vm_object_allocate(objtype_t type, vm_pindex_t size, vm_object_t object)
{
        int incr;

        RB_INIT(&object->rb_memq);
        LIST_INIT(&object->shadow_head);

        object->type = type;
        object->size = size;
        object->ref_count = 1;
        object->hold_count = 0;
        object->flags = 0;
        if ((object->type == OBJT_DEFAULT) || (object->type == OBJT_SWAP))
                vm_object_set_flag(object, OBJ_ONEMAPPING);
        object->paging_in_progress = 0;
        object->resident_page_count = 0;
        object->agg_pv_list_count = 0;
        object->shadow_count = 0;
        object->pg_color = next_index;
        if ( size > (PQ_L2_SIZE / 3 + PQ_PRIME1))
                incr = PQ_L2_SIZE / 3 + PQ_PRIME1;
        else
                incr = size;
        next_index = (next_index + incr) & PQ_L2_MASK;
        object->handle = NULL;
        object->backing_object = NULL;
        object->backing_object_offset = (vm_ooffset_t) 0;

        object->generation++;
        object->swblock_count = 0;
        RB_INIT(&object->swblock_root);
        vm_object_lock_init(object);

        lwkt_gettoken(&vmobj_token);
        TAILQ_INSERT_TAIL(&vm_object_list, object, object_list);
        vm_object_count++;
        lwkt_reltoken(&vmobj_token);
}

/*
 * Initialize the VM objects module.
 *
 * Called from the low level boot code only.
 */
void
vm_object_init(void)
{
        TAILQ_INIT(&vm_object_list);
        
        _vm_object_allocate(OBJT_DEFAULT, OFF_TO_IDX(KvaEnd),
                            &kernel_object);

        obj_zone = &obj_zone_store;
        zbootinit(obj_zone, "VM OBJECT", sizeof (struct vm_object),
                vm_objects_init, VM_OBJECTS_INIT);
}

void
vm_object_init2(void)
{
        zinitna(obj_zone, NULL, NULL, 0, 0, ZONE_PANICFAIL, 1);
}

/*
 * Allocate and return a new object of the specified type and size.
 *
 * No requirements.
 */
vm_object_t
vm_object_allocate(objtype_t type, vm_pindex_t size)
{
        vm_object_t result;

        result = (vm_object_t) zalloc(obj_zone);

        _vm_object_allocate(type, size, result);

        return (result);
}

/*
 * Add an additional reference to a vm_object.
 *
 * Object passed by caller must be stable or caller must already
 * hold vmobj_token to avoid races.
 */
void
vm_object_reference(vm_object_t object)
{
        lwkt_gettoken(&vmobj_token);
        vm_object_hold(object);
        vm_object_reference_locked(object);
        vm_object_drop(object);
        lwkt_reltoken(&vmobj_token);
}

void
vm_object_reference_locked(vm_object_t object)
{
        if (object) {
                ASSERT_LWKT_TOKEN_HELD(&vmobj_token);
                /*NOTYET*/
                /*ASSERT_LWKT_TOKEN_HELD(vm_object_token(object));*/
                object->ref_count++;
                if (object->type == OBJT_VNODE) {
                        vref(object->handle);
                        /* XXX what if the vnode is being destroyed? */
                }
        }
}

/*
 * Dereference an object and its underlying vnode.
 *
 * The caller must hold vmobj_token.
 * The object must be locked but not held.  This function will eat the lock.
 */
static void
vm_object_vndeallocate(vm_object_t object)
{
        struct vnode *vp = (struct vnode *) object->handle;

        KASSERT(object->type == OBJT_VNODE,
            ("vm_object_vndeallocate: not a vnode object"));
        KASSERT(vp != NULL, ("vm_object_vndeallocate: missing vp"));
        ASSERT_LWKT_TOKEN_HELD(&vmobj_token);
#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)
                vclrflags(vp, VTEXT);
        vm_object_unlock(object);
        vrele(vp);
}

/*
 * 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.
 *
 * The caller does not have to hold the object locked but must have control
 * over the reference in question in order to guarantee that the object
 * does not get ripped out from under us.
 */
void
vm_object_deallocate(vm_object_t object)
{
        lwkt_gettoken(&vmobj_token);
        vm_object_deallocate_locked(object);
        lwkt_reltoken(&vmobj_token);
}

void
vm_object_deallocate_locked(vm_object_t object)
{
        vm_object_t temp;

        ASSERT_LWKT_TOKEN_HELD(&vmobj_token);

        if (object)
                vm_object_lock(object);

        while (object != NULL) {
                if (object->type == OBJT_VNODE) {
                        vm_object_vndeallocate(object);
                        /* vndeallocate ate the lock */
                        break;
                }

                if (object->ref_count == 0) {
                        panic("vm_object_deallocate: object deallocated "
                              "too many times: %d", object->type);
                }
                if (object->ref_count > 2) {
                        object->ref_count--;
                        vm_object_unlock(object);
                        break;
                }

                /*
                 * We currently need the vm_token from this point on, and
                 * we must recheck ref_count after acquiring it.
                 */
                lwkt_gettoken(&vm_token);

                if (object->ref_count > 2) {
                        object->ref_count--;
                        lwkt_reltoken(&vm_token);
                        vm_object_unlock(object);
                        break;
                }

                /*
                 * Here on ref_count of one or two, which are special cases for
                 * objects.
                 *
                 * Nominal ref_count > 1 case if the second ref is not from
                 * a shadow.
                 */
                if (object->ref_count == 2 && object->shadow_count == 0) {
                        vm_object_set_flag(object, OBJ_ONEMAPPING);
                        object->ref_count--;
                        lwkt_reltoken(&vm_token);
                        vm_object_unlock(object);
                        break;
                }

                /*
                 * If the second ref is from a shadow we chain along it
                 * if object's handle is exhausted.
                 */
                if (object->ref_count == 2 && object->shadow_count == 1) {
                        if (object->handle == NULL &&
                            (object->type == OBJT_DEFAULT ||
                             object->type == OBJT_SWAP)) {
                                temp = LIST_FIRST(&object->shadow_head);
                                KASSERT(temp != NULL,
                                        ("vm_object_deallocate: ref_count: "
                                        "%d, shadow_count: %d",
                                        object->ref_count,
                                        object->shadow_count));
                                lwkt_reltoken(&vm_token);
                                vm_object_lock(temp);

                                if ((temp->handle == NULL) &&
                                    (temp->type == OBJT_DEFAULT ||
                                     temp->type == OBJT_SWAP)) {
                                        /*
                                         * Special case, must handle ref_count
                                         * manually to avoid recursion.
                                         */
                                        temp->ref_count++;
                                        vm_object_lock_swap();

                                        while (
                                                temp->paging_in_progress ||
                                                object->paging_in_progress
                                        ) {
                                                vm_object_pip_sleep(temp,
                                                                    "objde1");
                                                vm_object_pip_sleep(object,
                                                                    "objde2");
                                        }

                                        if (temp->ref_count == 1) {
                                                object->ref_count--;
                                                temp->ref_count--;
                                                vm_object_unlock(object);
                                                object = temp;
                                                goto doterm;
                                        }

                                        lwkt_gettoken(&vm_token);
                                        vm_object_collapse(temp);
                                        lwkt_reltoken(&vm_token);
                                        object->ref_count--;
                                        vm_object_unlock(object);
                                        object = temp;
                                        continue;
                                }
                                vm_object_unlock(temp);
                        } else {
                                lwkt_reltoken(&vm_token);
                        }
                        object->ref_count--;
                        vm_object_unlock(object);
                        break;
                }

                /*
                 * Normal dereferencing path
                 */
                object->ref_count--;
                if (object->ref_count != 0) {
                        lwkt_reltoken(&vm_token);
                        vm_object_unlock(object);
                        break;
                }

                /*
                 * Termination path
                 *
                 * We may have to loop to resolve races if we block getting
                 * temp's lock.  If temp is non NULL we have to swap the
                 * lock order so the original object lock as at the top
                 * of the lock heap.
                 */
                lwkt_reltoken(&vm_token);
doterm:
                while ((temp = object->backing_object) != NULL) {
                        vm_object_lock(temp);
                        if (temp == object->backing_object)
                                break;
                        vm_object_unlock(temp);
                }
                if (temp) {
                        LIST_REMOVE(object, shadow_list);
                        temp->shadow_count--;
                        temp->generation++;
                        object->backing_object = NULL;
                        vm_object_lock_swap();
                }

                /*
                 * 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);
                        /* termination ate the object lock */
                } else {
                        vm_object_unlock(object);
                }
                object = temp;
        }
}

/*
 * Destroy the specified object, freeing up related resources.
 *
 * The object must have zero references.
 *
 * The caller must be holding vmobj_token and properly interlock with
 * OBJ_DEAD (at the moment).
 *
 * The caller must have locked the object only, and not be holding it.
 * This function will eat the caller's lock on the object.
 */
static int vm_object_terminate_callback(vm_page_t p, void *data);

void
vm_object_terminate(vm_object_t object)
{
        /*
         * Make sure no one uses us.  Once we set OBJ_DEAD we should be
         * able to safely block.
         */
        KKASSERT((object->flags & OBJ_DEAD) == 0);
        ASSERT_LWKT_TOKEN_HELD(&vmobj_token);
        vm_object_set_flag(object, OBJ_DEAD);

        /*
         * Wait for the pageout daemon to be done with the object
         */
        vm_object_pip_wait(object, "objtrm1");

        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;

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

                vp = (struct vnode *) object->handle;
                vinvalbuf(vp, V_SAVE, 0, 0);
        }

        /*
         * Wait for any I/O to complete, after which there had better not
         * be any references left on the object.
         */
        vm_object_pip_wait(object, "objtrm2");

        if (object->ref_count != 0) {
                panic("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. 
         */
        lwkt_gettoken(&vm_token);
        vm_page_rb_tree_RB_SCAN(&object->rb_memq, NULL,
                                vm_object_terminate_callback, NULL);
        lwkt_reltoken(&vm_token);

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

        /*
         * Wait for the object hold count to hit zero, clean out pages as
         * we go.
         */
        lwkt_gettoken(&vm_token);
        for (;;) {
                vm_object_hold_wait(object);
                if (RB_ROOT(&object->rb_memq) == NULL)
                        break;
                kprintf("vm_object_terminate: Warning, object %p "
                        "still has %d pages\n",
                        object, object->resident_page_count);
                vm_page_rb_tree_RB_SCAN(&object->rb_memq, NULL,
                                        vm_object_terminate_callback, NULL);
        }
        lwkt_reltoken(&vm_token);

        /*
         * There had better not be any pages left
         */
        KKASSERT(object->resident_page_count == 0);

        /*
         * Remove the object from the global object list.
         *
         * (we are holding vmobj_token)
         */
        TAILQ_REMOVE(&vm_object_list, object, object_list);
        vm_object_count--;
        vm_object_dead_wakeup(object);
        vm_object_unlock(object);

        if (object->ref_count != 0) {
                panic("vm_object_terminate2: object with references, "
                      "ref_count=%d", object->ref_count);
        }

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

/*
 * The caller must hold vm_token.
 */
static int
vm_object_terminate_callback(vm_page_t p, void *data __unused)
{
        if (p->busy || (p->flags & PG_BUSY))
                panic("vm_object_terminate: freeing busy page %p", p);
        if (p->wire_count == 0) {
                vm_page_busy(p);
                vm_page_free(p);
                mycpu->gd_cnt.v_pfree++;
        } else {
                if (p->queue != PQ_NONE)
                        kprintf("vm_object_terminate: Warning: Encountered wired page %p on queue %d\n", p, p->queue);
                vm_page_busy(p);
                vm_page_remove(p);
                vm_page_wakeup(p);
        }
        return(0);
}

/*
 * The object is dead but still has an object<->pager association.  Sleep
 * and return.  The caller typically retests the association in a loop.
 *
 * Must be called with the vmobj_token held.
 */
void
vm_object_dead_sleep(vm_object_t object, const char *wmesg)
{
        ASSERT_LWKT_TOKEN_HELD(&vmobj_token);
        if (object->handle) {
                vm_object_set_flag(object, OBJ_DEADWNT);
                tsleep(object, 0, wmesg, 0);
                /* object may be invalid after this point */
        }
}

/*
 * Wakeup anyone waiting for the object<->pager disassociation on
 * a dead object.
 *
 * Must be called with the vmobj_token held.
 */
void
vm_object_dead_wakeup(vm_object_t object)
{
        ASSERT_LWKT_TOKEN_HELD(&vmobj_token);
        if (object->flags & OBJ_DEADWNT) {
                vm_object_clear_flag(object, OBJ_DEADWNT);
                wakeup(object);
        }
}

/*
 * 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 PG_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? XXX
 */
static int vm_object_page_clean_pass1(struct vm_page *p, void *data);
static int vm_object_page_clean_pass2(struct vm_page *p, void *data);

void
vm_object_page_clean(vm_object_t object, vm_pindex_t start, vm_pindex_t end,
                     int flags)
{
        struct rb_vm_page_scan_info info;
        struct vnode *vp;
        int wholescan;
        int pagerflags;
        int curgeneration;

        vm_object_hold(object);
        if (object->type != OBJT_VNODE ||
            (object->flags & OBJ_MIGHTBEDIRTY) == 0) {
                vm_object_drop(object);
                return;
        }

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

        vp = object->handle;

        /*
         * Interlock other major object operations.  This allows us to 
         * temporarily clear OBJ_WRITEABLE and OBJ_MIGHTBEDIRTY.
         */
        crit_enter();
        vm_object_set_flag(object, OBJ_CLEANING);

        /*
         * Handle 'entire object' case
         */
        info.start_pindex = start;
        if (end == 0) {
                info.end_pindex = object->size - 1;
        } else {
                info.end_pindex = end - 1;
        }
        wholescan = (start == 0 && info.end_pindex == object->size - 1);
        info.limit = flags;
        info.pagerflags = pagerflags;
        info.object = object;

        /*
         * If cleaning the entire object do a pass to mark the pages read-only.
         * If everything worked out ok, clear OBJ_WRITEABLE and
         * OBJ_MIGHTBEDIRTY.
         */
        if (wholescan) {
                info.error = 0;
                lwkt_gettoken(&vm_token);
                vm_page_rb_tree_RB_SCAN(&object->rb_memq, rb_vm_page_scancmp,
                                        vm_object_page_clean_pass1, &info);
                lwkt_reltoken(&vm_token);
                if (info.error == 0) {
                        vm_object_clear_flag(object,
                                             OBJ_WRITEABLE|OBJ_MIGHTBEDIRTY);
                        if (object->type == OBJT_VNODE &&
                            (vp = (struct vnode *)object->handle) != NULL) {
                                if (vp->v_flag & VOBJDIRTY) 
                                        vclrflags(vp, VOBJDIRTY);
                        }
                }
        }

        /*
         * Do a pass to clean all the dirty pages we find.
         */
        do {
                info.error = 0;
                curgeneration = object->generation;
                lwkt_gettoken(&vm_token);
                vm_page_rb_tree_RB_SCAN(&object->rb_memq, rb_vm_page_scancmp,
                                        vm_object_page_clean_pass2, &info);
                lwkt_reltoken(&vm_token);
        } while (info.error || curgeneration != object->generation);

        vm_object_clear_flag(object, OBJ_CLEANING);
        crit_exit();
        vm_object_drop(object);
}

/*
 * The caller must hold vm_token.
 */
static 
int
vm_object_page_clean_pass1(struct vm_page *p, void *data)
{
        struct rb_vm_page_scan_info *info = data;

        vm_page_flag_set(p, PG_CLEANCHK);
        if ((info->limit & OBJPC_NOSYNC) && (p->flags & PG_NOSYNC))
                info->error = 1;
        else
                vm_page_protect(p, VM_PROT_READ);       /* must not block */
        return(0);
}

/*
 * The caller must hold vm_token.
 */
static 
int
vm_object_page_clean_pass2(struct vm_page *p, void *data)
{
        struct rb_vm_page_scan_info *info = data;
        int n;

        /*
         * Do not mess with pages that were inserted after we started
         * the cleaning pass.
         */
        if ((p->flags & PG_CLEANCHK) == 0)
                return(0);

        /*
         * Before wasting time traversing the pmaps, check for trivial
         * cases where the page cannot be dirty.
         */
        if (p->valid == 0 || (p->queue - p->pc) == PQ_CACHE) {
                KKASSERT((p->dirty & p->valid) == 0);
                return(0);
        }

        /*
         * Check whether the page is dirty or not.  The page has been set
         * to be read-only so the check will not race a user dirtying the
         * page.
         */
        vm_page_test_dirty(p);
        if ((p->dirty & p->valid) == 0) {
                vm_page_flag_clear(p, PG_CLEANCHK);
                return(0);
        }

        /*
         * 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 (because pass1 will have returned an
         * error), so we do not have to set them.
         */
        if ((info->limit & OBJPC_NOSYNC) && (p->flags & PG_NOSYNC)) {
                vm_page_flag_clear(p, PG_CLEANCHK);
                return(0);
        }

        /*
         * Flush as many pages as we can.  PG_CLEANCHK will be cleared on
         * the pages that get successfully flushed.  Set info->error if
         * we raced an object modification.
         */
        n = vm_object_page_collect_flush(info->object, p, info->pagerflags);
        if (n == 0)
                info->error = 1;
        return(0);
}

/*
 * Collect the specified page and nearby pages and flush them out.
 * The number of pages flushed is returned.
 *
 * The caller must hold vm_token.
 */
static int
vm_object_page_collect_flush(vm_object_t object, vm_page_t p, int pagerflags)
{
        int runlen;
        int maxf;
        int chkb;
        int maxb;
        int i;
        int curgeneration;
        vm_pindex_t pi;
        vm_page_t maf[vm_pageout_page_count];
        vm_page_t mab[vm_pageout_page_count];
        vm_page_t ma[vm_pageout_page_count];

        curgeneration = object->generation;

        pi = p->pindex;
        while (vm_page_sleep_busy(p, TRUE, "vpcwai")) {
                if (object->generation != curgeneration) {
                        return(0);
                }
        }
        KKASSERT(p->object == object && p->pindex == pi);

        maxf = 0;
        for(i = 1; i < vm_pageout_page_count; i++) {
                vm_page_t tp;

                if ((tp = vm_page_lookup(object, pi + i)) != NULL) {
                        if ((tp->flags & PG_BUSY) ||
                                ((pagerflags & VM_PAGER_IGNORE_CLEANCHK) == 0 && 
                                 (tp->flags & PG_CLEANCHK) == 0) ||
                                (tp->busy != 0))
                                break;
                        if((tp->queue - tp->pc) == PQ_CACHE) {
                                vm_page_flag_clear(tp, PG_CLEANCHK);
                                break;
                        }
                        vm_page_test_dirty(tp);
                        if ((tp->dirty & tp->valid) == 0) {
                                vm_page_flag_clear(tp, PG_CLEANCHK);
                                break;
                        }
                        maf[ i - 1 ] = tp;
                        maxf++;
                        continue;
                }
                break;
        }

        maxb = 0;
        chkb = vm_pageout_page_count -  maxf;
        if (chkb) {
                for(i = 1; i < chkb;i++) {
                        vm_page_t tp;

                        if ((tp = vm_page_lookup(object, pi - i)) != NULL) {
                                if ((tp->flags & PG_BUSY) ||
                                        ((pagerflags & VM_PAGER_IGNORE_CLEANCHK) == 0 && 
                                         (tp->flags & PG_CLEANCHK) == 0) ||
                                        (tp->busy != 0))
                                        break;
                                if((tp->queue - tp->pc) == PQ_CACHE) {
                                        vm_page_flag_clear(tp, PG_CLEANCHK);
                                        break;
                                }
                                vm_page_test_dirty(tp);
                                if ((tp->dirty & tp->valid) == 0) {
                                        vm_page_flag_clear(tp, PG_CLEANCHK);
                                        break;
                                }
                                mab[ i - 1 ] = tp;
                                maxb++;
                                continue;
                        }
                        break;
                }
        }

        for(i = 0; i < maxb; i++) {
                int index = (maxb - i) - 1;
                ma[index] = mab[i];
                vm_page_flag_clear(ma[index], PG_CLEANCHK);
        }
        vm_page_flag_clear(p, PG_CLEANCHK);
        ma[maxb] = p;
        for(i = 0; i < maxf; i++) {
                int index = (maxb + i) + 1;
                ma[index] = maf[i];
                vm_page_flag_clear(ma[index], PG_CLEANCHK);
        }
        runlen = maxb + maxf + 1;

        vm_pageout_flush(ma, runlen, pagerflags);
        for (i = 0; i < runlen; i++) {
                if (ma[i]->valid & ma[i]->dirty) {
                        vm_page_protect(ma[i], VM_PROT_READ);
                        vm_page_flag_set(ma[i], PG_CLEANCHK);

                        /*
                         * maxf will end up being the actual number of pages
                         * we wrote out contiguously, non-inclusive of the
                         * first page.  We do not count look-behind pages.
                         */
                        if (i >= maxb + 1 && (maxf > i - maxb - 1))
                                maxf = i - maxb - 1;
                }
        }
        return(maxf + 1);
}

/*
 * Same as vm_object_pmap_copy, except range checking really
 * works, and is meant for small sections of an object.
 *
 * This code protects resident pages by making them read-only
 * and is typically called on a fork or split when a page
 * is converted to copy-on-write.  
 *
 * NOTE: If the page is already at VM_PROT_NONE, calling
 * vm_page_protect will have no effect.
 */
void
vm_object_pmap_copy_1(vm_object_t object, vm_pindex_t start, vm_pindex_t end)
{
        vm_pindex_t idx;
        vm_page_t p;

        if (object == NULL || (object->flags & OBJ_WRITEABLE) == 0)
                return;

        /*
         * spl protection needed to prevent races between the lookup,
         * an interrupt unbusy/free, and our protect call.
         */
        crit_enter();
        lwkt_gettoken(&vm_token);
        for (idx = start; idx < end; idx++) {
                p = vm_page_lookup(object, idx);
                if (p == NULL)
                        continue;
                vm_page_protect(p, VM_PROT_READ);
        }
        lwkt_reltoken(&vm_token);
        crit_exit();
}

/*
 * Removes all physical pages in the specified object range from all
 * physical maps.
 *
 * The object must *not* be locked.
 */

static int vm_object_pmap_remove_callback(vm_page_t p, void *data);

void
vm_object_pmap_remove(vm_object_t object, vm_pindex_t start, vm_pindex_t end)
{
        struct rb_vm_page_scan_info info;

        if (object == NULL)
                return;
        info.start_pindex = start;
        info.end_pindex = end - 1;

        crit_enter();
        lwkt_gettoken(&vm_token);
        vm_page_rb_tree_RB_SCAN(&object->rb_memq, rb_vm_page_scancmp,
                                vm_object_pmap_remove_callback, &info);
        if (start == 0 && end == object->size)
                vm_object_clear_flag(object, OBJ_WRITEABLE);
        lwkt_reltoken(&vm_token);
        crit_exit();
}

/*
 * The caller must hold vm_token.
 */
static int
vm_object_pmap_remove_callback(vm_page_t p, void *data __unused)
{
        vm_page_protect(p, VM_PROT_NONE);
        return(0);
}

/*
 * 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.
 *
 * No requirements.
 */
void
vm_object_madvise(vm_object_t object, vm_pindex_t pindex, int count, int advise)
{
        vm_pindex_t end, tpindex;
        vm_object_t tobject;
        vm_page_t m;

        if (object == NULL)
                return;

        end = pindex + count;

        lwkt_gettoken(&vm_token);

        /*
         * 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) {
                                continue;
                        }
                }

                /*
                 * spl protection is required to avoid a race between the
                 * lookup, an interrupt unbusy/free, and our busy check.
                 */

                crit_enter();
                m = vm_page_lookup(tobject, tpindex);

                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
                         */
                        crit_exit();
                        if (tobject->backing_object == NULL)
                                continue;
                        tpindex += OFF_TO_IDX(tobject->backing_object_offset);
                        tobject = tobject->backing_object;
                        goto shadowlookup;
                }

                /*
                 * If the page is busy or not in a normal active state,
                 * we skip it.  If the page is not managed there are no
                 * page queues to mess with.  Things can break if we mess
                 * with pages in any of the below states.
                 */
                if (
                    m->hold_count ||
                    m->wire_count ||
                    (m->flags & PG_UNMANAGED) ||
                    m->valid != VM_PAGE_BITS_ALL
                ) {
                        crit_exit();
                        continue;
                }

                if (vm_page_sleep_busy(m, TRUE, "madvpo")) {
                        crit_exit();
                        goto relookup;
                }
                vm_page_busy(m);
                crit_exit();

                /*
                 * Theoretically once a page is known not to be busy, an
                 * interrupt cannot come along and rip it out from under us.
                 */

                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);
                        if (tobject->type == OBJT_SWAP)
                                swap_pager_freespace(tobject, tpindex, 1);
                }
                vm_page_wakeup(m);
        }       
        lwkt_reltoken(&vm_token);
}

/*
 * 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.
 *
 * No other requirements.
 */
void
vm_object_shadow(vm_object_t *object, vm_ooffset_t *offset, 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.
         */
        lwkt_gettoken(&vm_token);

        if (source != NULL &&
            source->ref_count == 1 &&
            source->handle == NULL &&
            (source->type == OBJT_DEFAULT ||
             source->type == OBJT_SWAP)) {
                lwkt_reltoken(&vm_token);
                return;
        }

        /*
         * Allocate a new object with the given length
         */

        if ((result = vm_object_allocate(OBJT_DEFAULT, length)) == NULL)
                panic("vm_object_shadow: no object for shadowing");

        /*
         * 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;
        if (source) {
                LIST_INSERT_HEAD(&source->shadow_head, result, shadow_list);
                source->shadow_count++;
                source->generation++;
                result->pg_color = (source->pg_color + OFF_TO_IDX(*offset)) & PQ_L2_MASK;
        }

        /*
         * Store the offset into the source object, and fix up the offset into
         * the new object.
         */
        result->backing_object_offset = *offset;
        lwkt_reltoken(&vm_token);

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

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

static int vm_object_backing_scan_callback(vm_page_t p, void *data);

/*
 * The caller must hold vm_token.
 */
static __inline int
vm_object_backing_scan(vm_object_t object, int op)
{
        struct rb_vm_page_scan_info info;
        vm_object_t backing_object;

        crit_enter();

        backing_object = object->backing_object;
        info.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
                 * 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) {
                        crit_exit();
                        return(0);
                }
        }
        if (op & OBSC_COLLAPSE_WAIT) {
                KKASSERT((backing_object->flags & OBJ_DEAD) == 0);
                vm_object_set_flag(backing_object, OBJ_DEAD);
        }

        /*
         * Our scan.   We have to retry if a negative error code is returned,
         * otherwise 0 or 1 will be returned in info.error.  0 Indicates that
         * the scan had to be stopped because the parent does not completely
         * shadow the child.
         */
        info.object = object;
        info.backing_object = backing_object;
        info.limit = op;
        do {
                info.error = 1;
                vm_page_rb_tree_RB_SCAN(&backing_object->rb_memq, NULL,
                                        vm_object_backing_scan_callback,
                                        &info);
        } while (info.error < 0);
        crit_exit();
        return(info.error);
}

/*
 * The caller must hold vm_token.
 */
static int
vm_object_backing_scan_callback(vm_page_t p, void *data)
{
        struct rb_vm_page_scan_info *info = data;
        vm_object_t backing_object;
        vm_object_t object;
        vm_pindex_t new_pindex;
        vm_pindex_t backing_offset_index;
        int op;

        new_pindex = p->pindex - info->backing_offset_index;
        op = info->limit;
        object = info->object;
        backing_object = info->backing_object;
        backing_offset_index = info->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
                ) {
                        return(0);
                }

                /*
                 * 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)
                ) {
                        info->error = 0;        /* problemo */
                        return(-1);             /* stop the scan */
                }
        }

        /*
         * Check for busy page
         */

        if (op & (OBSC_COLLAPSE_WAIT | OBSC_COLLAPSE_NOWAIT)) {
                vm_page_t pp;

                if (op & OBSC_COLLAPSE_NOWAIT) {
                        if (
                            (p->flags & PG_BUSY) ||
                            !p->valid || 
                            p->hold_count || 
                            p->wire_count ||
                            p->busy
                        ) {
                                return(0);
                        }
                } else if (op & OBSC_COLLAPSE_WAIT) {
                        if (vm_page_sleep_busy(p, TRUE, "vmocol")) {
                                /*
                                 * If we slept, anything could have
                                 * happened.   Ask that the scan be restarted.
                                 *
                                 * Since the object is marked dead, the
                                 * backing offset should not have changed.  
                                 */
                                info->error = -1;
                                return(-1);
                        }
                }

                /* 
                 * Busy the page
                 */
                vm_page_busy(p);

                KASSERT(
                    p->object == backing_object,
                    ("vm_object_qcollapse(): 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_protect(p, VM_PROT_NONE);
                        vm_page_free(p);
                        return(0);
                }

                pp = vm_page_lookup(object, new_pindex);
                if (pp != NULL || vm_pager_has_page(object, new_pindex)) {
                        /*
                         * 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_protect(p, VM_PROT_NONE);
                        vm_page_free(p);
                        return(0);
                }

                /*
                 * 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.
                 */
                if ((p->queue - p->pc) == PQ_CACHE)
                        vm_page_deactivate(p);

                vm_page_rename(p, object, new_pindex);
                /* page automatically made dirty by rename */
        }
        return(0);
}

/*
 * 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.
 *
 * The caller must hold vm_token and vmobj_token.
 * (only called from vm_object_collapse)
 */
static void
vm_object_qcollapse(vm_object_t object)
{
        vm_object_t backing_object = object->backing_object;

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

        backing_object->ref_count += 2;

        vm_object_backing_scan(object, OBSC_COLLAPSE_NOWAIT);

        backing_object->ref_count -= 2;
}

/*
 * Collapse an object with the object backing it.  Pages in the backing
 * object are moved into the parent, and the backing object is deallocated.
 *
 * The caller must hold (object).
 */
void
vm_object_collapse(vm_object_t object)
{
        ASSERT_LWKT_TOKEN_HELD(&vm_token);
        ASSERT_LWKT_TOKEN_HELD(&vmobj_token);
        vm_object_assert_held(object);

        while (TRUE) {
                vm_object_t backing_object;

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

                if ((backing_object = object->backing_object) == NULL)
                        break;

                vm_object_hold(backing_object);
                if (backing_object != object->backing_object) {
                        vm_object_drop(backing_object);
                        continue;
                }

                /*
                 * we check the backing object first, because it is most likely
                 * not collapsable.
                 */
                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_drop(backing_object);
                        break;
                }

                if (
                    object->paging_in_progress != 0 ||
                    backing_object->paging_in_progress != 0
                ) {
                        vm_object_drop(backing_object);
                        vm_object_qcollapse(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);

                        /*
                         * Move the pager from backing_object to object.
                         */

                        if (backing_object->type == OBJT_SWAP) {
                                vm_object_pip_add(backing_object, 1);

                                /*
                                 * scrap the paging_offset junk and do a 
                                 * discrete copy.  This also removes major 
                                 * assumptions about how the swap-pager 
                                 * works from where it doesn't belong.  The
                                 * new swapper is able to optimize the
                                 * destroy-source case.
                                 */

                                vm_object_pip_add(object, 1);
                                swap_pager_copy(
                                    backing_object,
                                    object,
                                    OFF_TO_IDX(object->backing_object_offset), TRUE);
                                vm_object_pip_wakeup(object);

                                vm_object_pip_wakeup(backing_object);
                        }
                        /*
                         * 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);
                        object->backing_object->shadow_count--;
                        object->backing_object->generation++;
                        if (backing_object->backing_object) {
                                LIST_REMOVE(backing_object, shadow_list);
                                backing_object->backing_object->shadow_count--;
                                backing_object->backing_object->generation++;
                        }
                        object->backing_object = backing_object->backing_object;
                        if (object->backing_object) {
                                LIST_INSERT_HEAD(
                                    &object->backing_object->shadow_head,
                                    object, 
                                    shadow_list
                                );
                                object->backing_object->shadow_count++;
                                object->backing_object->generation++;
                        }

                        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));
                        KASSERT(RB_EMPTY(&backing_object->rb_memq),
                                ("backing_object %p somehow has left "
                                 "over pages during collapse!",
                                 backing_object));

                        /*
                         * Wait for hold count to hit zero
                         */
                        vm_object_drop(backing_object);
                        vm_object_hold_wait(backing_object);

                        /* (we are holding vmobj_token) */
                        TAILQ_REMOVE(&vm_object_list, backing_object,
                                     object_list);
                        vm_object_count--;

                        zfree(obj_zone, 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 (vm_object_backing_scan(object, OBSC_TEST_ALL_SHADOWED) == 0) {
                                vm_object_drop(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--;
                        backing_object->generation++;

                        new_backing_object = backing_object->backing_object;
                        if ((object->backing_object = new_backing_object) != NULL) {
                                vm_object_reference(new_backing_object);
                                LIST_INSERT_HEAD(
                                    &new_backing_object->shadow_head,
                                    object,
                                    shadow_list
                                );
                                new_backing_object->shadow_count++;
                                new_backing_object->generation++;
                                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;
                         * so we don't need to call vm_object_deallocate, but
                         * we do anyway.
                         */
                        vm_object_drop(backing_object);
                        vm_object_deallocate_locked(backing_object);
                        object_bypasses++;
                }

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

/*
 * Removes all physical pages in the specified object range from the
 * object's list of pages.
 *
 * No requirements.
 */
static int vm_object_page_remove_callback(vm_page_t p, void *data);

void
vm_object_page_remove(vm_object_t object, vm_pindex_t start, vm_pindex_t end,
                      boolean_t clean_only)
{
        struct rb_vm_page_scan_info info;
        int all;

        /*
         * Degenerate cases and assertions
         */
        lwkt_gettoken(&vm_token);
        if (object == NULL ||
            (object->resident_page_count == 0 && object->swblock_count == 0)) {
                lwkt_reltoken(&vm_token);
                return;
        }
        KASSERT(object->type != OBJT_PHYS, 
                ("attempt to remove pages from a physical object"));

        /*
         * Indicate that paging is occuring on the object
         */
        crit_enter();
        vm_object_pip_add(object, 1);

        /*
         * Figure out the actual removal range and whether we are removing
         * the entire contents of the object or not.  If removing the entire
         * contents, be sure to get all pages, even those that might be 
         * beyond the end of the object.
         */
        info.start_pindex = start;
        if (end == 0)
                info.end_pindex = (vm_pindex_t)-1;
        else
                info.end_pindex = end - 1;
        info.limit = clean_only;
        all = (start == 0 && info.end_pindex >= object->size - 1);

        /*
         * Loop until we are sure we have gotten them all.
         */
        do {
                info.error = 0;
                vm_page_rb_tree_RB_SCAN(&object->rb_memq, rb_vm_page_scancmp,
                                        vm_object_page_remove_callback, &info);
        } while (info.error);

        /*
         * Remove any related swap if throwing away pages, or for
         * non-swap objects (the swap is a clean copy in that case).
         */
        if (object->type != OBJT_SWAP || clean_only == FALSE) {
                if (all)
                        swap_pager_freespace_all(object);
                else
                        swap_pager_freespace(object, info.start_pindex,
                             info.end_pindex - info.start_pindex + 1);
        }

        /*
         * Cleanup
         */
        vm_object_pip_wakeup(object);
        crit_exit();
        lwkt_reltoken(&vm_token);
}

/*
 * The caller must hold vm_token.
 */
static int
vm_object_page_remove_callback(vm_page_t p, void *data)
{
        struct rb_vm_page_scan_info *info = data;

        /*
         * Wired pages cannot be destroyed, but they can be invalidated
         * and we do so if clean_only (limit) is not set.
         *
         * WARNING!  The page may be wired due to being part of a buffer
         *           cache buffer, and the buffer might be marked B_CACHE.
         *           This is fine as part of a truncation but VFSs must be
         *           sure to fix the buffer up when re-extending the file.
         */
        if (p->wire_count != 0) {
                vm_page_protect(p, VM_PROT_NONE);
                if (info->limit == 0)
                        p->valid = 0;
                return(0);
        }

        /*
         * The busy flags are only cleared at
         * interrupt -- minimize the spl transitions
         */

        if (vm_page_sleep_busy(p, TRUE, "vmopar")) {
                info->error = 1;
                return(0);
        }

        /*
         * limit is our clean_only flag.  If set and the page is dirty, do
         * not free it.  If set and the page is being held by someone, do
         * not free it.
         */
        if (info->limit && p->valid) {
                vm_page_test_dirty(p);
                if (p->valid & p->dirty)
                        return(0);
                if (p->hold_count)
                        return(0);
        }

        /*
         * Destroy the page
         */
        vm_page_busy(p);
        vm_page_protect(p, VM_PROT_NONE);
        vm_page_free(p);
        return(0);
}

/*
 * 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
 *      next_object     Second object into coalesce
 *      next_offset     Offset into next_object
 *
 *      prev_size       Size of reference to prev_object
 *      next_size       Size of reference to next_object
 *
 * The caller must hold vm_token and vmobj_token.
 *
 * The caller does not need to hold (prev_object) but must have a stable
 * pointer to it (typically by holding the vm_map locked).
 */
boolean_t
vm_object_coalesce(vm_object_t prev_object, vm_pindex_t prev_pindex,
                   vm_size_t prev_size, vm_size_t next_size)
{
        vm_pindex_t next_pindex;

        ASSERT_LWKT_TOKEN_HELD(&vm_token);
        ASSERT_LWKT_TOKEN_HELD(&vmobj_token);

        if (prev_object == NULL) {
                return (TRUE);
        }

        vm_object_hold(prev_object);

        if (prev_object->type != OBJT_DEFAULT &&
            prev_object->type != OBJT_SWAP) {
                vm_object_drop(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_drop(prev_object);
                return (FALSE);
        }

        prev_size >>= PAGE_SHIFT;
        next_size >>= PAGE_SHIFT;
        next_pindex = prev_pindex + prev_size;

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

        /*
         * 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);
        }

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

        vm_object_drop(prev_object);
        return (TRUE);
}

/*
 * Make the object writable and flag is being possibly dirty.
 *
 * No requirements.
 */
void
vm_object_set_writeable_dirty(vm_object_t object)
{
        struct vnode *vp;

        lwkt_gettoken(&vm_token);
        vm_object_set_flag(object, OBJ_WRITEABLE|OBJ_MIGHTBEDIRTY);
        if (object->type == OBJT_VNODE &&
            (vp = (struct vnode *)object->handle) != NULL) {
                if ((vp->v_flag & VOBJDIRTY) == 0) {
                        vsetflags(vp, VOBJDIRTY);
                }
        }
        lwkt_reltoken(&vm_token);
}

#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);
static int      vm_object_in_map (vm_object_t object);

/*
 * The caller must hold vm_token.
 */
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;
                }
                return (0);
        }
        switch(entry->maptype) {
        case VM_MAPTYPE_SUBMAP:
                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;
                }
                break;
        case VM_MAPTYPE_NORMAL:
        case VM_MAPTYPE_VPAGETABLE:
                obj = entry->object.vm_object;
                while (obj) {
                        if (obj == object)
                                return 1;
                        obj = obj->backing_object;
                }
                break;
        default:
                break;
        }
        return 0;
}

static int vm_object_in_map_callback(struct proc *p, void *data);

struct vm_object_in_map_info {
        vm_object_t object;
        int rv;
};

/*
 * Debugging only
 */
static int
vm_object_in_map(vm_object_t object)
{
        struct vm_object_in_map_info info;

        info.rv = 0;
        info.object = object;

        allproc_scan(vm_object_in_map_callback, &info);
        if (info.rv)
                return 1;
        if( _vm_object_in_map(&kernel_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;
}

/*
 * Debugging only
 */
static int
vm_object_in_map_callback(struct proc *p, void *data)
{
        struct vm_object_in_map_info *info = data;

        if (p->p_vmspace) {
                if (_vm_object_in_map(&p->p_vmspace->vm_map, info->object, 0)) {
                        info->rv = 1;
                        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.
         */
        for (object = TAILQ_FIRST(&vm_object_list);
                        object != NULL;
                        object = TAILQ_NEXT(object, object_list)) {
                if (object->type == OBJT_MARKER)
                        continue;
                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);
                        }
                }
        }
}

/*
 * Debugging only
 */
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%lx, res=%d, ref=%d, flags=0x%x\n",
            object, (int)object->type, (u_long)object->size,
            object->resident_page_count, object->ref_count, object->flags);
        /*
         * XXX no %qd in kernel.  Truncate object->backing_object_offset.
         */
        db_iprintf(" sref=%d, backing_object(%d)=(%p)+0x%lx\n",
            object->shadow_count, 
            object->backing_object ? object->backing_object->ref_count : 0,
            object->backing_object, (long)object->backing_object_offset);

        if (!full)
                return;

        db_indent += 2;
        count = 0;
        RB_FOREACH(p, vm_page_rb_tree, &object->rb_memq) {
                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%lx,page=0x%lx)",
                    (u_long) p->pindex, (u_long) 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.
 *
 * Debugging only
 */
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);
}

/*
 * Debugging only
 */
DB_SHOW_COMMAND(vmopag, vm_object_print_pages)
{
        vm_object_t object;
        int nl = 0;
        int c;
        for (object = TAILQ_FIRST(&vm_object_list);
                        object != NULL;
                        object = TAILQ_NEXT(object, object_list)) {
                vm_pindex_t idx, fidx;
                vm_pindex_t osize;
                vm_paddr_t pa = -1, padiff;
                int rcount;
                vm_page_t m;

                if (object->type == OBJT_MARKER)
                        continue;
                db_printf("new object: %p\n", (void *)object);
                if ( nl > 18) {
                        c = cngetc();
                        if (c != ' ')
                                return;
                        nl = 0;
                }
                nl++;
                rcount = 0;
                fidx = 0;
                osize = object->size;
                if (osize > 128)
                        osize = 128;
                for (idx = 0; idx < osize; idx++) {
                        m = vm_page_lookup(object, idx);
                        if (m == NULL) {
                                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;
                                }
                                continue;
                        }

                                
                        if (rcount &&
                                (VM_PAGE_TO_PHYS(m) == pa + rcount * PAGE_SIZE)) {
                                ++rcount;
                                continue;
                        }
                        if (rcount) {
                                padiff = pa + rcount * PAGE_SIZE - VM_PAGE_TO_PHYS(m);
                                padiff >>= PAGE_SHIFT;
                                padiff &= PQ_L2_MASK;
                                if (padiff == 0) {
                                        pa = VM_PAGE_TO_PHYS(m) - rcount * PAGE_SIZE;
                                        ++rcount;
                                        continue;
                                }
                                db_printf(" index(%ld)run(%d)pa(0x%lx)",
                                        (long)fidx, rcount, (long)pa);
                                db_printf("pd(%ld)\n", (long)padiff);
                                if ( nl > 18) {
                                        c = cngetc();
                                        if (c != ' ')
                                                return;
                                        nl = 0;
                                }
                                nl++;
                        }
                        fidx = idx;
                        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 */