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.
     * 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.
     *
     * $FreeBSD$
     */
    
    /*
     *      Virtual memory object module.
     */
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/proc.h>           /* for curproc, pageproc */
    #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 <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
    
    #define MSYNC_FLUSH_HARDSEQ     0x01
    #define MSYNC_FLUSH_SOFTSEQ     0x02
    
    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 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);
   
   /*
    *      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;
   #ifndef NULL_SIMPLELOCKS
   static struct simplelock vm_object_list_lock;
   #endif
   static long vm_object_count;            /* count of all objects */
   vm_object_t kernel_object;
   vm_object_t kmem_object;
   static struct vm_object kernel_object_store;
   static struct vm_object kmem_object_store;
   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;
   static int object_hash_rand;
   #define VM_OBJECTS_INIT 256
   static struct vm_object vm_objects_init[VM_OBJECTS_INIT];
   
   void
   _vm_object_allocate(type, size, object)
           objtype_t type;
           vm_size_t size;
           vm_object_t object;
   {
           int incr;
           TAILQ_INIT(&object->memq);
           LIST_INIT(&object->shadow_head);
   
           object->type = type;
           object->size = size;
           object->ref_count = 1;
           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->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;
           /*
            * Try to generate a number that will spread objects out in the
            * hash table.  We 'wipe' new objects across the hash in 128 page
            * increments plus 1 more to offset it a little more by the time
            * it wraps around.
            */
           object->hash_rand = object_hash_rand - 129;
   
           object->generation++;
   
           TAILQ_INSERT_TAIL(&vm_object_list, object, object_list);
           vm_object_count++;
           object_hash_rand = object->hash_rand;
   }
   
   /*
    *      vm_object_init:
    *
    *      Initialize the VM objects module.
    */
   void
   vm_object_init()
   {
           TAILQ_INIT(&vm_object_list);
           simple_lock_init(&vm_object_list_lock);
           vm_object_count = 0;
           
           kernel_object = &kernel_object_store;
           _vm_object_allocate(OBJT_DEFAULT, OFF_TO_IDX(VM_MAX_KERNEL_ADDRESS - VM_MIN_KERNEL_ADDRESS),
               kernel_object);
   
           kmem_object = &kmem_object_store;
           _vm_object_allocate(OBJT_DEFAULT, OFF_TO_IDX(VM_MAX_KERNEL_ADDRESS - VM_MIN_KERNEL_ADDRESS),
               kmem_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() {
           zinitna(obj_zone, NULL, NULL, 0, 0, 0, 1);
   }
   
   /*
    *      vm_object_allocate:
    *
    *      Returns a new object with the given size.
    */
   
   vm_object_t
   vm_object_allocate(type, size)
           objtype_t type;
           vm_size_t size;
   {
           vm_object_t result;
   
           result = (vm_object_t) zalloc(obj_zone);
   
           _vm_object_allocate(type, size, result);
   
           return (result);
   }
   
   
   /*
    *      vm_object_reference:
    *
    *      Gets another reference to the given object.
    */
   void
   vm_object_reference(object)
           vm_object_t object;
   {
           if (object == NULL)
                   return;
   
   #if 0
           /* object can be re-referenced during final cleaning */
           KASSERT(!(object->flags & OBJ_DEAD),
               ("vm_object_reference: attempting to reference dead obj"));
   #endif
   
           object->ref_count++;
           if (object->type == OBJT_VNODE) {
                   while (vget((struct vnode *) object->handle, LK_RETRY|LK_NOOBJ, curproc)) {
                           printf("vm_object_reference: delay in getting object\n");
                   }
           }
   }
   
   void
   vm_object_vndeallocate(object)
           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"));
   #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) {
                   vp->v_flag &= ~VTEXT;
                   vm_object_clear_flag(object, OBJ_OPT);
           }
           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(object)
           vm_object_t object;
   {
           vm_object_t temp;
   
           while (object != NULL) {
   
                   if (object->type == OBJT_VNODE) {
                           vm_object_vndeallocate(object);
                           return;
                   }
   
                   if (object->ref_count == 0) {
                           panic("vm_object_deallocate: object deallocated too many times: %d", object->type);
                   } else if (object->ref_count > 2) {
                           object->ref_count--;
                           return;
                   }
   
                   /*
                    * Here on ref_count of one or two, which are special cases for
                    * objects.
                    */
                   if ((object->ref_count == 2) && (object->shadow_count == 0)) {
                           vm_object_set_flag(object, OBJ_ONEMAPPING);
                           object->ref_count--;
                           return;
                   } else if ((object->ref_count == 2) && (object->shadow_count == 1)) {
                           object->ref_count--;
                           if ((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 ((robject->handle == NULL) &&
                                       (robject->type == OBJT_DEFAULT ||
                                        robject->type == OBJT_SWAP)) {
   
                                           robject->ref_count++;
   
                                           while (
                                                   robject->paging_in_progress ||
                                                   object->paging_in_progress
                                           ) {
                                                   vm_object_pip_sleep(robject, "objde1");
                                                   vm_object_pip_sleep(object, "objde2");
                                           }
   
                                           if (robject->ref_count == 1) {
                                                   robject->ref_count--;
                                                   object = robject;
                                                   goto doterm;
                                           }
   
                                           object = robject;
                                           vm_object_collapse(object);
                                           continue;
                                   }
                           }
   
                           return;
   
                   } else {
                           object->ref_count--;
                           if (object->ref_count != 0)
                                   return;
                   }
   
   doterm:
   
                   temp = object->backing_object;
                   if (temp) {
                           LIST_REMOVE(object, shadow_list);
                           temp->shadow_count--;
                           if (temp->ref_count == 0)
                                   vm_object_clear_flag(temp, OBJ_OPT);
                           temp->generation++;
                           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);
                   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(object)
           vm_object_t object;
   {
           vm_page_t p;
           int s;
   
           /*
            * 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;
   
                   /*
                    * Freeze optimized copies.
                    */
                   vm_freeze_copyopts(object, 0, object->size);
   
                   /*
                    * Clean pages and flush buffers.
                    */
                   vm_object_page_clean(object, 0, 0, OBJPC_SYNC);
   
                   vp = (struct vnode *) object->handle;
                   vinvalbuf(vp, V_SAVE, NOCRED, NULL, 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, "objtrm");
   
           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. 
            */
           s = splvm();
           while ((p = TAILQ_FIRST(&object->memq)) != NULL) {
                   if (p->busy || (p->flags & PG_BUSY))
                           panic("vm_object_terminate: freeing busy page %p\n", p);
                   if (p->wire_count == 0) {
                           vm_page_busy(p);
                           vm_page_free(p);
                           cnt.v_pfree++;
                   } else {
                           vm_page_busy(p);
                           vm_page_remove(p);
                   }
           }
           splx(s);
   
           /*
            * Let the pager know object is dead.
            */
           vm_pager_deallocate(object);
   
           /*
            * Remove the object from the global object list.
            */
           simple_lock(&vm_object_list_lock);
           TAILQ_REMOVE(&vm_object_list, object, object_list);
           simple_unlock(&vm_object_list_lock);
   
           wakeup(object);
   
           /*
            * Free the space for the object.
            */
           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 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.
    */
   
   void
   vm_object_page_clean(object, start, end, flags)
           vm_object_t object;
           vm_pindex_t start;
           vm_pindex_t end;
           int flags;
   {
           vm_page_t p, np;
           vm_offset_t tstart, tend;
           vm_pindex_t pi;
           struct vnode *vp;
           int clearobjflags;
           int pagerflags;
           int curgeneration;
   
           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;
   
           vp = object->handle;
   
           vm_object_set_flag(object, OBJ_CLEANING);
   
           /*
            * Handle 'entire object' case
            */
           tstart = start;
           if (end == 0) {
                   tend = object->size;
           } else {
                   tend = end;
           }
   
           /*
            * 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_offset_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 ||
                               (p->queue - p->pc) == PQ_CACHE) {
                                   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->flags & PG_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_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;
   
           for(p = TAILQ_FIRST(&object->memq); p; p = TAILQ_NEXT(p, listq)) {
                   vm_page_flag_set(p, PG_CLEANCHK);
                   if ((flags & OBJPC_NOSYNC) && (p->flags & PG_NOSYNC))
                           clearobjflags = 0;
                   else
                           vm_page_protect(p, VM_PROT_READ);
           }
   
           if (clearobjflags && (tstart == 0) && (tend == object->size)) {
                   struct vnode *vp;
   
                   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) {
                                   simple_lock(&vp->v_interlock);
                                   vp->v_flag &= ~VOBJDIRTY;
                                   simple_unlock(&vp->v_interlock);
                           }
                   }
           }
   
   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->flags & PG_CLEANCHK) == 0) ||
                           (pi < tstart) || (pi >= tend) ||
                           (p->valid == 0) ||
                           ((p->queue - p->pc) == PQ_CACHE)) {
                           vm_page_flag_clear(p, PG_CLEANCHK);
                           continue;
                   }
   
                   vm_page_test_dirty(p);
                   if ((p->dirty & p->valid) == 0) {
                           vm_page_flag_clear(p, PG_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->flags & PG_NOSYNC)) {
                           vm_page_flag_clear(p, PG_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;
                   }
           }
   
   #if 0
           VOP_FSYNC(vp, NULL, (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 s;
           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];
   
           s = splvm();
           pi = p->pindex;
           while (vm_page_sleep_busy(p, TRUE, "vpcwai")) {
                   if (object->generation != curgeneration) {
                           splx(s);
                           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->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;
   
           splx(s);
           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);
   }
   
   #ifdef not_used
   /* XXX I cannot tell if this should be an exported symbol */
   /*
    *      vm_object_deactivate_pages
    *
    *      Deactivate all pages in the specified object.  (Keep its pages
    *      in memory even though it is no longer referenced.)
    *
    *      The object must be locked.
    */
   static void
   vm_object_deactivate_pages(object)
           vm_object_t object;
   {
           vm_page_t p, next;
   
           for (p = TAILQ_FIRST(&object->memq); p != NULL; p = next) {
                   next = TAILQ_NEXT(p, listq);
                   vm_page_deactivate(p);
           }
   }
   #endif
   
   /*
    * 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(object, start, end)
           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;
   
           for (idx = start; idx < end; idx++) {
                   p = vm_page_lookup(object, idx);
                   if (p == NULL)
                           continue;
                   vm_page_protect(p, VM_PROT_READ);
           }
   }
   
   /*
    *      vm_object_pmap_remove:
    *
    *      Removes all physical pages in the specified
    *      object range from all physical maps.
    *
    *      The object must *not* be locked.
    */
   void
   vm_object_pmap_remove(object, start, end)
           vm_object_t object;
           vm_pindex_t start;
           vm_pindex_t end;
   {
           vm_page_t p;
   
           if (object == NULL)
                   return;
           for (p = TAILQ_FIRST(&object->memq);
                   p != NULL;
                   p = TAILQ_NEXT(p, listq)) {
                   if (p->pindex >= start && p->pindex < end)
                           vm_page_protect(p, VM_PROT_NONE);
           }
           if ((start == 0) && (object->size == end))
                   vm_object_clear_flag(object, OBJ_WRITEABLE);
   }
   
   /*
    *      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(object, pindex, count, advise)
           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;
   
           /*
            * 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;
                           }
                   }
   
                   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
                            */
                           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
                   ) {
                           continue;
                   }
   
                   if (vm_page_sleep_busy(m, TRUE, "madvpo"))
                          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);
                          if (tobject->type == OBJT_SWAP)
                                  swap_pager_freespace(tobject, tpindex, 1);
                  }
          }       
  }
  
  /*
   *      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(object, offset, length)
          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 &&
              source->ref_count == 1 &&
              source->handle == NULL &&
              (source->type == OBJT_DEFAULT ||
               source->type == OBJT_SWAP))
                  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;
  
          /*
           * 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 __inline int
  vm_object_backing_scan(vm_object_t object, int op)
  {
          int s;
          int r = 1;
          vm_page_t p;
          vm_object_t backing_object;
          vm_pindex_t backing_offset_index;
  
          s = splvm();
  
          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
                   * 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) {
                          splx(s);
                          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->flags & PG_BUSY) ||
                                      !p->valid || 
                                      p->hold_count || 
                                      p->wire_count ||
                                      p->busy
                                  ) {
                                          p = next;
                                          continue;
                                  }
                          } else if (op & OBSC_COLLAPSE_WAIT) {
                                  if (vm_page_sleep_busy(p, TRUE, "vmocol")) {
                                          /*
                                           * 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;
                                  }
                          }
  
                          /* 
                           * 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);
                                  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_protect(p, VM_PROT_NONE);
                                  vm_page_free(p);
                                  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.
                           */
                          if ((p->queue - p->pc) == PQ_CACHE)
                                  vm_page_deactivate(p);
  
                          vm_page_rename(p, object, new_pindex);
                          /* page automatically made dirty by rename */
                  }
                  p = next;
          }
          splx(s);
          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(object)
          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;
  }
  
  /*
   *      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(object)
          vm_object_t 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;
  
                  /*
                   * 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)) {
                          break;
                  }
  
                  if (
                      object->paging_in_progress != 0 ||
                      backing_object->paging_in_progress != 0
                  ) {
                          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(TAILQ_FIRST(&backing_object->memq) == NULL, ("backing_object %p somehow has left over pages during collapse!", backing_object));
                          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) {
                                  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_deallocate(backing_object);
                          object_bypasses++;
                  }
  
                  /*
                   * Try again with this object's new backing object.
                   */
          }
  }
  
  /*
   *      vm_object_page_remove: [internal]
   *
   *      Removes all physical pages in the specified
   *      object range from the object's list of pages.
   *
   *      The object must be locked.
   */
  void
  vm_object_page_remove(object, start, end, clean_only)
          vm_object_t object;
          vm_pindex_t start;
          vm_pindex_t end;
          boolean_t clean_only;
  {
          vm_page_t p, next;
          unsigned int size;
          int all;
  
          if (object == NULL ||
              object->resident_page_count == 0)
                  return;
  
          all = ((end == 0) && (start == 0));
  
          /*
           * 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, ("attempt to remove pages from a physical object"));
  
          vm_object_pip_add(object, 1);
  again:
          size = end - start;
          if (all || size > object->resident_page_count / 4) {
                  for (p = TAILQ_FIRST(&object->memq); p != NULL; p = next) {
                          next = TAILQ_NEXT(p, listq);
                          if (all || ((start <= p->pindex) && (p->pindex < end))) {
                                  if (p->wire_count != 0) {
                                          vm_page_protect(p, VM_PROT_NONE);
                                          if (!clean_only)
                                                  p->valid = 0;
                                          continue;
                                  }
  
                                  /*
                                   * The busy flags are only cleared at
                                   * interrupt -- minimize the spl transitions
                                   */
  
                                  if (vm_page_sleep_busy(p, TRUE, "vmopar"))
                                          goto again;
  
                                  if (clean_only && p->valid) {
                                          vm_page_test_dirty(p);
                                          if (p->valid & p->dirty)
                                                  continue;
                                  }
  
                                  vm_page_busy(p);
                                  vm_page_protect(p, VM_PROT_NONE);
                                  vm_page_free(p);
                          }
                  }
          } else {
                  while (size > 0) {
                          if ((p = vm_page_lookup(object, start)) != 0) {
  
                                  if (p->wire_count != 0) {
                                          vm_page_protect(p, VM_PROT_NONE);
                                          if (!clean_only)
                                                  p->valid = 0;
                                          start += 1;
                                          size -= 1;
                                          continue;
                                  }
  
                                  /*
                                   * The busy flags are only cleared at
                                   * interrupt -- minimize the spl transitions
                                   */
                                  if (vm_page_sleep_busy(p, TRUE, "vmopar"))
                                          goto again;
  
                                  if (clean_only && p->valid) {
                                          vm_page_test_dirty(p);
                                          if (p->valid & p->dirty) {
                                                  start += 1;
                                                  size -= 1;
                                                  continue;
                                          }
                                  }
  
                                  vm_page_busy(p);
                                  vm_page_protect(p, VM_PROT_NONE);
                                  vm_page_free(p);
                          }
                          start += 1;
                          size -= 1;
                  }
          }
          vm_object_pip_wakeup(object);
  }
  
  /*
   *      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
   *              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
   *
   *      Conditions:
   *      The object must *not* be locked.
   */
  boolean_t
  vm_object_coalesce(prev_object, prev_pindex, prev_size, next_size)
          vm_object_t prev_object;
          vm_pindex_t prev_pindex;
          vm_size_t prev_size, next_size;
  {
          vm_pindex_t next_pindex;
  
          if (prev_object == NULL) {
                  return (TRUE);
          }
  
          if (prev_object->type != OBJT_DEFAULT &&
              prev_object->type != OBJT_SWAP) {
                  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) {
                  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)) {
                  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;
  
          return (TRUE);
  }
  
  void
  vm_object_set_writeable_dirty(vm_object_t object)
  {
          struct vnode *vp;
  
          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) {
                          simple_lock(&vp->v_interlock);
                          vp->v_flag |= VOBJDIRTY;
                          simple_unlock(&vp->v_interlock);
                  }
          }
  }
  
  
  
  #include "opt_ddb.h"
  #ifdef DDB
  #include <sys/kernel.h>
  
  #include <sys/cons.h>
  
  #include <ddb/ddb.h>
  
  static int      _vm_object_in_map __P((vm_map_t map, vm_object_t object,
                                         vm_map_entry_t entry));
  static int      vm_object_in_map __P((vm_object_t object));
  
  static int
  _vm_object_in_map(map, object, entry)
          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( object)
          vm_object_t object;
  {
          struct proc *p;
          for (p = allproc.lh_first; p != 0; p = p->p_list.le_next) {
                  if( !p->p_vmspace /* || (p->p_flag & (P_SYSTEM|P_WEXIT)) */)
                          continue;
                  if( _vm_object_in_map(&p->p_vmspace->vm_map, object, 0))
                          return 1;
          }
          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;
          if( _vm_object_in_map( mb_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.
           */
          for (object = TAILQ_FIRST(&vm_object_list);
                          object != NULL;
                          object = TAILQ_NEXT(object, 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%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;
          for (p = TAILQ_FIRST(&object->memq); p != NULL; p = TAILQ_NEXT(p, 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%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. */
  void
  vm_object_print(addr, have_addr, count, modif)
          /* 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;
          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;
  
                  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 */

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