FreeBSD/Linux Kernel Cross Reference
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 <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/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/uma.h>
    
    #define EASY_SCAN_FACTOR       8
    
    #define MSYNC_FLUSH_HARDSEQ     0x01
    #define MSYNC_FLUSH_SOFTSEQ     0x02
    
   /*
    * msync / VM object flushing optimizations
    */
   static int msync_flush_flags = MSYNC_FLUSH_HARDSEQ | MSYNC_FLUSH_SOFTSEQ;
   SYSCTL_INT(_vm, OID_AUTO, msync_flush_flags,
           CTLFLAG_RW, &msync_flush_flags, 0, "");
   
   static int old_msync;
   SYSCTL_INT(_vm, OID_AUTO, old_msync, CTLFLAG_RW, &old_msync, 0,
       "Use old (insecure) msync behavior");
   
   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 curgeneration, int pagerflags);
   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));
           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->flags = 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;
           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);
   
           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);
   
           /*
            * 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;
   }
   
   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)
   {
           struct vnode *vp;
   
           if (object == NULL)
                   return;
           VM_OBJECT_LOCK(object);
           object->ref_count++;
           if (object->type == OBJT_VNODE) {
                   int vfslocked;
   
                   vp = object->handle;
                   VM_OBJECT_UNLOCK(object);
                   vfslocked = VFS_LOCK_GIANT(vp->v_mount);
                   vget(vp, LK_RETRY, curthread);
                   VFS_UNLOCK_GIANT(vfslocked);
           } else
                   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);
           KASSERT((object->flags & OBJ_DEAD) == 0,
               ("vm_object_reference_locked: dead object referenced"));
           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) {
                                   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--;
                           temp->generation++;
                           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_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, NULL, 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->flags %x\n", p, p->busy, p->flags));
                   if (p->wire_count == 0) {
                           vm_page_free(p);
                           cnt.v_pfree++;
                   } else {
                           vm_page_remove(p);
                   }
           }
           vm_page_unlock_queues();
   
           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);
   
           /*
            * 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);
   
           /*
            * Free the space for the object.
            */
           uma_zfree(obj_zone, 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 p, np;
           vm_pindex_t tstart, tend;
           vm_pindex_t pi;
           int clearobjflags;
           int pagerflags;
           int curgeneration;
   
           VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
           if (object->type != OBJT_VNODE ||
                   (object->flags & OBJ_MIGHTBEDIRTY) == 0)
                   return;
   
           pagerflags = (flags & (OBJPC_SYNC | OBJPC_INVAL)) ? VM_PAGER_PUT_SYNC : VM_PAGER_CLUSTER_OK;
           pagerflags |= (flags & OBJPC_INVAL) ? VM_PAGER_PUT_INVAL : 0;
   
           vm_object_set_flag(object, OBJ_CLEANING);
   
           tstart = start;
           if (end == 0) {
                   tend = object->size;
           } else {
                   tend = end;
           }
   
           vm_page_lock_queues();
           /*
            * If the caller is smart and only msync()s a range he knows is
            * dirty, we may be able to avoid an object scan.  This results in
            * a phenominal improvement in performance.  We cannot do this
            * as a matter of course because the object may be huge - e.g.
            * the size might be in the gigabytes or terrabytes.
            */
           if (msync_flush_flags & MSYNC_FLUSH_HARDSEQ) {
                   vm_pindex_t tscan;
                   int scanlimit;
                   int scanreset;
   
                   scanreset = object->resident_page_count / EASY_SCAN_FACTOR;
                   if (scanreset < 16)
                           scanreset = 16;
                   pagerflags |= VM_PAGER_IGNORE_CLEANCHK;
   
                   scanlimit = scanreset;
                   tscan = tstart;
                   while (tscan < tend) {
                           curgeneration = object->generation;
                           p = vm_page_lookup(object, tscan);
                           if (p == NULL || p->valid == 0) {
                                   if (--scanlimit == 0)
                                           break;
                                   ++tscan;
                                   continue;
                           }
                           vm_page_test_dirty(p);
                           if ((p->dirty & p->valid) == 0) {
                                   if (--scanlimit == 0)
                                           break;
                                   ++tscan;
                                   continue;
                           }
                           /*
                            * If we have been asked to skip nosync pages and 
                            * this is a nosync page, we can't continue.
                            */
                           if ((flags & OBJPC_NOSYNC) && (p->oflags & VPO_NOSYNC)) {
                                   if (--scanlimit == 0)
                                           break;
                                   ++tscan;
                                   continue;
                           }
                           scanlimit = scanreset;
   
                           /*
                            * This returns 0 if it was unable to busy the first
                            * page (i.e. had to sleep).
                            */
                           tscan += vm_object_page_collect_flush(object, p, curgeneration, pagerflags);
                   }
   
                   /*
                    * If everything was dirty and we flushed it successfully,
                    * and the requested range is not the entire object, we
                    * don't have to mess with CLEANCHK or MIGHTBEDIRTY and can
                    * return immediately.
                    */
                   if (tscan >= tend && (tstart || tend < object->size)) {
                           vm_page_unlock_queues();
                           vm_object_clear_flag(object, OBJ_CLEANING);
                           return;
                   }
                   pagerflags &= ~VM_PAGER_IGNORE_CLEANCHK;
           }
   
           /*
            * Generally set CLEANCHK interlock and 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;
           TAILQ_FOREACH(p, &object->memq, listq) {
                   p->oflags |= VPO_CLEANCHK;
                   if ((flags & OBJPC_NOSYNC) && (p->oflags & VPO_NOSYNC))
                           clearobjflags = 0;
                   else
                           pmap_remove_write(p);
           }
   
           if (clearobjflags && (tstart == 0) && (tend == object->size)) {
                   struct vnode *vp;
   
                   vm_object_clear_flag(object, OBJ_MIGHTBEDIRTY);
                   if (object->type == OBJT_VNODE &&
                       (vp = (struct vnode *)object->handle) != NULL) {
                           VI_LOCK(vp);
                           if (vp->v_iflag & VI_OBJDIRTY)
                                   vp->v_iflag &= ~VI_OBJDIRTY;
                           VI_UNLOCK(vp);
                   }
           }
   
   rescan:
           curgeneration = object->generation;
   
           for (p = TAILQ_FIRST(&object->memq); p; p = np) {
                   int n;
   
                   np = TAILQ_NEXT(p, listq);
   
   again:
                   pi = p->pindex;
                   if ((p->oflags & VPO_CLEANCHK) == 0 ||
                           (pi < tstart) || (pi >= tend) ||
                       p->valid == 0) {
                           p->oflags &= ~VPO_CLEANCHK;
                           continue;
                   }
   
                   vm_page_test_dirty(p);
                   if ((p->dirty & p->valid) == 0) {
                           p->oflags &= ~VPO_CLEANCHK;
                           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) && (p->oflags & VPO_NOSYNC)) {
                           p->oflags &= ~VPO_CLEANCHK;
                           continue;
                   }
   
                   n = vm_object_page_collect_flush(object, p,
                           curgeneration, pagerflags);
                   if (n == 0)
                           goto rescan;
   
                   if (object->generation != curgeneration)
                           goto rescan;
   
                   /*
                    * Try to optimize the next page.  If we can't we pick up
                    * our (random) scan where we left off.
                    */
                   if (msync_flush_flags & MSYNC_FLUSH_SOFTSEQ) {
                           if ((p = vm_page_lookup(object, pi + n)) != NULL)
                                   goto again;
                   }
           }
           vm_page_unlock_queues();
   #if 0
           VOP_FSYNC(vp, (pagerflags & VM_PAGER_PUT_SYNC)?MNT_WAIT:0, curproc);
   #endif
   
           vm_object_clear_flag(object, OBJ_CLEANING);
           return;
   }
   
   static int
   vm_object_page_collect_flush(vm_object_t object, vm_page_t p, int curgeneration, int pagerflags)
   {
           int runlen;
           int maxf;
           int chkb;
           int maxb;
           int i;
           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];
   
           mtx_assert(&vm_page_queue_mtx, MA_OWNED);
           pi = p->pindex;
           while (vm_page_sleep_if_busy(p, TRUE, "vpcwai")) {
                   vm_page_lock_queues();
                   if (object->generation != curgeneration) {
                           return(0);
                   }
           }
           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->oflags & VPO_BUSY) ||
                                   ((pagerflags & VM_PAGER_IGNORE_CLEANCHK) == 0 &&
                                    (tp->oflags & VPO_CLEANCHK) == 0) ||
                                   (tp->busy != 0))
                                   break;
                           vm_page_test_dirty(tp);
                           if ((tp->dirty & tp->valid) == 0) {
                                   tp->oflags &= ~VPO_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->oflags & VPO_BUSY) ||
                                           ((pagerflags & VM_PAGER_IGNORE_CLEANCHK) == 0 &&
                                            (tp->oflags & VPO_CLEANCHK) == 0) ||
                                           (tp->busy != 0))
                                           break;
                                   vm_page_test_dirty(tp);
                                   if ((tp->dirty & tp->valid) == 0) {
                                           tp->oflags &= ~VPO_CLEANCHK;
                                           break;
                                   }
                                   mab[ i - 1 ] = tp;
                                   maxb++;
                                   continue;
                           }
                           break;
                   }
           }
   
           for(i = 0; i < maxb; i++) {
                   int index = (maxb - i) - 1;
                   ma[index] = mab[i];
                   ma[index]->oflags &= ~VPO_CLEANCHK;
           }
           p->oflags &= ~VPO_CLEANCHK;
           ma[maxb] = p;
           for(i = 0; i < maxf; i++) {
                   int index = (maxb + i) + 1;
                   ma[index] = maf[i];
                   ma[index]->oflags &= ~VPO_CLEANCHK;
           }
           runlen = maxb + maxf + 1;
   
           vm_pageout_flush(ma, runlen, pagerflags);
           for (i = 0; i < runlen; i++) {
                   if (ma[i]->valid & ma[i]->dirty) {
                           pmap_remove_write(ma[i]);
                           ma[i]->oflags |= VPO_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);
   }
   
   /*
    * 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, curthread);
                  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, curthread);
                  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;
                          }
                  }
                  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;
                  }
                  /*
                   * 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.
                   */
                  vm_page_lock_queues();
                  if (m->hold_count ||
                      m->wire_count ||
                      (m->flags & PG_UNMANAGED) ||
                      m->valid != VM_PAGE_BITS_ALL) {
                          vm_page_unlock_queues();
                          goto unlock_tobject;
                  }
                  if ((m->oflags & VPO_BUSY) || m->busy) {
                          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++;
                  source->generation++;
                  result->flags |= source->flags & OBJ_NEEDGIANT;
                  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++;
                  source->generation++;
                  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;
          }
          new_object->flags |= orig_object->flags & OBJ_NEEDGIANT;
  retry:
          if ((m = TAILQ_FIRST(&orig_object->memq)) != NULL) {
                  if (m->pindex < offidxstart) {
                          m = vm_page_splay(offidxstart, orig_object->root);
                          if ((orig_object->root = m)->pindex < offidxstart)
                                  m = TAILQ_NEXT(m, listq);
                  }
          }
          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_flag_set(m, PG_REFERENCED);
                          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_page_lock_queues();
                                          vm_page_flag_set(p, PG_REFERENCED);
                                          vm_page_unlock_queues();
                                          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;
                          }
  
                          /*
                           * 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);
  
                          /*
                           * 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--;
                          backing_object->generation++;
                          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.
                                   */
                                  backing_object->backing_object->generation++;
                                  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);
  
                          mtx_lock(&vm_object_list_mtx);
                          TAILQ_REMOVE(
                              &vm_object_list, 
                              backing_object,
                              object_list
                          );
                          mtx_unlock(&vm_object_list_mtx);
  
                          uma_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 (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--;
                          backing_object->generation++;
  
                          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++;
                                  new_backing_object->generation++;
                                  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:
   *
   *      Removes all physical pages in the given range from the
   *      object's list of pages.  If the range's end is zero, all
   *      physical pages from the range's start to the end of the object
   *      are deleted.
   *
   *      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;
  
          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:
          vm_page_lock_queues();
          if ((p = TAILQ_FIRST(&object->memq)) != NULL) {
                  if (p->pindex < start) {
                          p = vm_page_splay(start, object->root);
                          if ((object->root = p)->pindex < start)
                                  p = TAILQ_NEXT(p, listq);
                  }
          }
          /*
           * 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 (p->wire_count != 0) {
                          pmap_remove_all(p);
                          if (!clean_only)
                                  p->valid = 0;
                          continue;
                  }
                  if (vm_page_sleep_if_busy(p, TRUE, "vmopar"))
                          goto again;
                  if (clean_only && p->valid) {
                          pmap_remove_write(p);
                          if (p->valid & p->dirty)
                                  continue;
                  }
                  pmap_remove_all(p);
                  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);
  }
  
  /*
   *      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
   *
   *      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)
  {
          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);
          }
  
          /*
           * 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_UNLOCK(prev_object);
          return (TRUE);
  }
  
  void
  vm_object_set_writeable_dirty(vm_object_t object)
  {
          struct vnode *vp;
  
          VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
          if ((object->flags & OBJ_MIGHTBEDIRTY) != 0)
                  return;
          vm_object_set_flag(object, OBJ_MIGHTBEDIRTY);
          if (object->type == OBJT_VNODE &&
              (vp = (struct vnode *)object->handle) != NULL) {
                  VI_LOCK(vp);
                  vp->v_iflag |= VI_OBJDIRTY;
                  VI_UNLOCK(vp);
          }
  }
  
  #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\n",
              object, (int)object->type, (uintmax_t)object->size,
              object->resident_page_count, object->ref_count, object->flags);
          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;
          int nl = 0;
          int c;
  
          TAILQ_FOREACH(object, &vm_object_list, object_list) {
                  vm_pindex_t idx, fidx;
                  vm_pindex_t osize;
                  vm_paddr_t pa = -1;
                  int rcount;
                  vm_page_t m;
  
                  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) {
                                  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 = 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 */

Cache object: 985b6e7839af8f2e9d822fcf895cc8f4