FreeBSD/Linux Kernel Cross Reference
sys/vm/vm_page.c

     /*-
      * Copyright (c) 1991 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_page.c     7.4 (Berkeley) 5/7/91
     */
    
    /*-
     * 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.
     */
    
    /*
     *                      GENERAL RULES ON VM_PAGE MANIPULATION
     *
     *      - a pageq mutex is required when adding or removing a page from a
     *        page queue (vm_page_queue[]), regardless of other mutexes or the
     *        busy state of a page.
     *
     *      - a hash chain mutex is required when associating or disassociating
     *        a page from the VM PAGE CACHE hash table (vm_page_buckets),
     *        regardless of other mutexes or the busy state of a page.
     *
     *      - either a hash chain mutex OR a busied page is required in order
     *        to modify the page flags.  A hash chain mutex must be obtained in
     *        order to busy a page.  A page's flags cannot be modified by a
     *        hash chain mutex if the page is marked busy.
     *
     *      - The object memq mutex is held when inserting or removing
     *        pages from an object (vm_page_insert() or vm_page_remove()).  This
     *        is different from the object's main mutex.
     *
     *      Generally speaking, you have to be aware of side effects when running
     *      vm_page ops.  A vm_page_lookup() will return with the hash chain
     *      locked, whether it was able to lookup the page or not.  vm_page_free(),
     *      vm_page_cache(), vm_page_activate(), and a number of other routines
     *      will release the hash chain mutex for you.  Intermediate manipulation
     *      routines such as vm_page_flag_set() expect the hash chain to be held
     *      on entry and the hash chain will remain held on return.
     *
     *      pageq scanning can only occur with the pageq in question locked.
     *      We have a known bottleneck with the active queue, but the cache
     *      and free queues are actually arrays already. 
     */
    
    /*
     *      Resident memory management module.
     */
    
    #include <sys/cdefs.h>
   __FBSDID("$FreeBSD: releng/5.4/sys/vm/vm_page.c 142975 2005-03-02 04:00:04Z alc $");
   
   #include <sys/param.h>
   #include <sys/systm.h>
   #include <sys/lock.h>
   #include <sys/malloc.h>
   #include <sys/mutex.h>
   #include <sys/proc.h>
   #include <sys/vmmeter.h>
   #include <sys/vnode.h>
   
   #include <vm/vm.h>
   #include <vm/vm_param.h>
   #include <vm/vm_kern.h>
   #include <vm/vm_object.h>
   #include <vm/vm_page.h>
   #include <vm/vm_pageout.h>
   #include <vm/vm_pager.h>
   #include <vm/vm_extern.h>
   #include <vm/uma.h>
   #include <vm/uma_int.h>
   
   /*
    *      Associated with page of user-allocatable memory is a
    *      page structure.
    */
   
   struct mtx vm_page_queue_mtx;
   struct mtx vm_page_queue_free_mtx;
   
   vm_page_t vm_page_array = 0;
   int vm_page_array_size = 0;
   long first_page = 0;
   int vm_page_zero_count = 0;
   
   /*
    *      vm_set_page_size:
    *
    *      Sets the page size, perhaps based upon the memory
    *      size.  Must be called before any use of page-size
    *      dependent functions.
    */
   void
   vm_set_page_size(void)
   {
           if (cnt.v_page_size == 0)
                   cnt.v_page_size = PAGE_SIZE;
           if (((cnt.v_page_size - 1) & cnt.v_page_size) != 0)
                   panic("vm_set_page_size: page size not a power of two");
   }
   
   /*
    *      vm_page_startup:
    *
    *      Initializes the resident memory module.
    *
    *      Allocates memory for the page cells, and
    *      for the object/offset-to-page hash table headers.
    *      Each page cell is initialized and placed on the free list.
    */
   vm_offset_t
   vm_page_startup(vm_offset_t vaddr)
   {
           vm_offset_t mapped;
           vm_size_t npages;
           vm_paddr_t page_range;
           vm_paddr_t new_end;
           int i;
           vm_paddr_t pa;
           int nblocks;
           vm_paddr_t last_pa;
   
           /* the biggest memory array is the second group of pages */
           vm_paddr_t end;
           vm_paddr_t biggestsize;
           int biggestone;
   
           vm_paddr_t total;
           vm_size_t bootpages;
   
           total = 0;
           biggestsize = 0;
           biggestone = 0;
           nblocks = 0;
           vaddr = round_page(vaddr);
   
           for (i = 0; phys_avail[i + 1]; i += 2) {
                   phys_avail[i] = round_page(phys_avail[i]);
                   phys_avail[i + 1] = trunc_page(phys_avail[i + 1]);
           }
   
           for (i = 0; phys_avail[i + 1]; i += 2) {
                   vm_paddr_t size = phys_avail[i + 1] - phys_avail[i];
   
                   if (size > biggestsize) {
                           biggestone = i;
                           biggestsize = size;
                   }
                   ++nblocks;
                   total += size;
           }
   
           end = phys_avail[biggestone+1];
   
           /*
            * Initialize the locks.
            */
           mtx_init(&vm_page_queue_mtx, "vm page queue mutex", NULL, MTX_DEF |
               MTX_RECURSE);
           mtx_init(&vm_page_queue_free_mtx, "vm page queue free mutex", NULL,
               MTX_SPIN);
   
           /*
            * Initialize the queue headers for the free queue, the active queue
            * and the inactive queue.
            */
           vm_pageq_init();
   
           /*
            * Allocate memory for use when boot strapping the kernel memory
            * allocator.
            */
           bootpages = UMA_BOOT_PAGES * UMA_SLAB_SIZE;
           new_end = end - bootpages;
           new_end = trunc_page(new_end);
           mapped = pmap_map(&vaddr, new_end, end,
               VM_PROT_READ | VM_PROT_WRITE);
           bzero((caddr_t) mapped, end - new_end);
           uma_startup((caddr_t)mapped);
   
           /*
            * Compute the number of pages of memory that will be available for
            * use (taking into account the overhead of a page structure per
            * page).
            */
           first_page = phys_avail[0] / PAGE_SIZE;
           page_range = phys_avail[(nblocks - 1) * 2 + 1] / PAGE_SIZE - first_page;
           npages = (total - (page_range * sizeof(struct vm_page)) -
               (end - new_end)) / PAGE_SIZE;
           end = new_end;
   
           /*
            * Reserve an unmapped guard page to trap access to vm_page_array[-1].
            */
           vaddr += PAGE_SIZE;
   
           /*
            * Initialize the mem entry structures now, and put them in the free
            * queue.
            */
           new_end = trunc_page(end - page_range * sizeof(struct vm_page));
           mapped = pmap_map(&vaddr, new_end, end,
               VM_PROT_READ | VM_PROT_WRITE);
           vm_page_array = (vm_page_t) mapped;
           phys_avail[biggestone + 1] = new_end;
   
           /*
            * Clear all of the page structures
            */
           bzero((caddr_t) vm_page_array, page_range * sizeof(struct vm_page));
           vm_page_array_size = page_range;
   
           /*
            * Construct the free queue(s) in descending order (by physical
            * address) so that the first 16MB of physical memory is allocated
            * last rather than first.  On large-memory machines, this avoids
            * the exhaustion of low physical memory before isa_dmainit has run.
            */
           cnt.v_page_count = 0;
           cnt.v_free_count = 0;
           for (i = 0; phys_avail[i + 1] && npages > 0; i += 2) {
                   pa = phys_avail[i];
                   last_pa = phys_avail[i + 1];
                   while (pa < last_pa && npages-- > 0) {
                           vm_pageq_add_new_page(pa);
                           pa += PAGE_SIZE;
                   }
           }
           return (vaddr);
   }
   
   void
   vm_page_flag_set(vm_page_t m, unsigned short bits)
   {
   
           mtx_assert(&vm_page_queue_mtx, MA_OWNED);
           m->flags |= bits;
   } 
   
   void
   vm_page_flag_clear(vm_page_t m, unsigned short bits)
   {
   
           mtx_assert(&vm_page_queue_mtx, MA_OWNED);
           m->flags &= ~bits;
   }
   
   void
   vm_page_busy(vm_page_t m)
   {
   
           VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
           KASSERT((m->flags & PG_BUSY) == 0,
               ("vm_page_busy: page already busy!!!"));
           vm_page_flag_set(m, PG_BUSY);
   }
   
   /*
    *      vm_page_flash:
    *
    *      wakeup anyone waiting for the page.
    */
   void
   vm_page_flash(vm_page_t m)
   {
   
           VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
           if (m->flags & PG_WANTED) {
                   vm_page_flag_clear(m, PG_WANTED);
                   wakeup(m);
           }
   }
   
   /*
    *      vm_page_wakeup:
    *
    *      clear the PG_BUSY flag and wakeup anyone waiting for the
    *      page.
    *
    */
   void
   vm_page_wakeup(vm_page_t m)
   {
   
           VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
           KASSERT(m->flags & PG_BUSY, ("vm_page_wakeup: page not busy!!!"));
           vm_page_flag_clear(m, PG_BUSY);
           vm_page_flash(m);
   }
   
   void
   vm_page_io_start(vm_page_t m)
   {
   
           VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
           m->busy++;
   }
   
   void
   vm_page_io_finish(vm_page_t m)
   {
   
           VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
           mtx_assert(&vm_page_queue_mtx, MA_OWNED);
           m->busy--;
           if (m->busy == 0)
                   vm_page_flash(m);
   }
   
   /*
    * Keep page from being freed by the page daemon
    * much of the same effect as wiring, except much lower
    * overhead and should be used only for *very* temporary
    * holding ("wiring").
    */
   void
   vm_page_hold(vm_page_t mem)
   {
   
           mtx_assert(&vm_page_queue_mtx, MA_OWNED);
           mem->hold_count++;
   }
   
   void
   vm_page_unhold(vm_page_t mem)
   {
   
           mtx_assert(&vm_page_queue_mtx, MA_OWNED);
           --mem->hold_count;
           KASSERT(mem->hold_count >= 0, ("vm_page_unhold: hold count < 0!!!"));
           if (mem->hold_count == 0 && mem->queue == PQ_HOLD)
                   vm_page_free_toq(mem);
   }
   
   /*
    *      vm_page_free:
    *
    *      Free a page
    *
    *      The clearing of PG_ZERO is a temporary safety until the code can be
    *      reviewed to determine that PG_ZERO is being properly cleared on
    *      write faults or maps.  PG_ZERO was previously cleared in
    *      vm_page_alloc().
    */
   void
   vm_page_free(vm_page_t m)
   {
           vm_page_flag_clear(m, PG_ZERO);
           vm_page_free_toq(m);
           vm_page_zero_idle_wakeup();
   }
   
   /*
    *      vm_page_free_zero:
    *
    *      Free a page to the zerod-pages queue
    */
   void
   vm_page_free_zero(vm_page_t m)
   {
           vm_page_flag_set(m, PG_ZERO);
           vm_page_free_toq(m);
   }
   
   /*
    *      vm_page_sleep_if_busy:
    *
    *      Sleep and release the page queues lock if PG_BUSY is set or,
    *      if also_m_busy is TRUE, busy is non-zero.  Returns TRUE if the
    *      thread slept and the page queues lock was released.
    *      Otherwise, retains the page queues lock and returns FALSE.
    */
   int
   vm_page_sleep_if_busy(vm_page_t m, int also_m_busy, const char *msg)
   {
           vm_object_t object;
   
           mtx_assert(&vm_page_queue_mtx, MA_OWNED);
           VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
           if ((m->flags & PG_BUSY) || (also_m_busy && m->busy)) {
                   vm_page_flag_set(m, PG_WANTED | PG_REFERENCED);
                   /*
                    * It's possible that while we sleep, the page will get
                    * unbusied and freed.  If we are holding the object
                    * lock, we will assume we hold a reference to the object
                    * such that even if m->object changes, we can re-lock
                    * it.
                    */
                   object = m->object;
                   VM_OBJECT_UNLOCK(object);
                   msleep(m, &vm_page_queue_mtx, PDROP | PVM, msg, 0);
                   VM_OBJECT_LOCK(object);
                   return (TRUE);
           }
           return (FALSE);
   }
   
   /*
    *      vm_page_dirty:
    *
    *      make page all dirty
    */
   void
   vm_page_dirty(vm_page_t m)
   {
           KASSERT(m->queue - m->pc != PQ_CACHE,
               ("vm_page_dirty: page in cache!"));
           KASSERT(m->queue - m->pc != PQ_FREE,
               ("vm_page_dirty: page is free!"));
           m->dirty = VM_PAGE_BITS_ALL;
   }
   
   /*
    *      vm_page_splay:
    *
    *      Implements Sleator and Tarjan's top-down splay algorithm.  Returns
    *      the vm_page containing the given pindex.  If, however, that
    *      pindex is not found in the vm_object, returns a vm_page that is
    *      adjacent to the pindex, coming before or after it.
    */
   vm_page_t
   vm_page_splay(vm_pindex_t pindex, vm_page_t root)
   {
           struct vm_page dummy;
           vm_page_t lefttreemax, righttreemin, y;
   
           if (root == NULL)
                   return (root);
           lefttreemax = righttreemin = &dummy;
           for (;; root = y) {
                   if (pindex < root->pindex) {
                           if ((y = root->left) == NULL)
                                   break;
                           if (pindex < y->pindex) {
                                   /* Rotate right. */
                                   root->left = y->right;
                                   y->right = root;
                                   root = y;
                                   if ((y = root->left) == NULL)
                                           break;
                           }
                           /* Link into the new root's right tree. */
                           righttreemin->left = root;
                           righttreemin = root;
                   } else if (pindex > root->pindex) {
                           if ((y = root->right) == NULL)
                                   break;
                           if (pindex > y->pindex) {
                                   /* Rotate left. */
                                   root->right = y->left;
                                   y->left = root;
                                   root = y;
                                   if ((y = root->right) == NULL)
                                           break;
                           }
                           /* Link into the new root's left tree. */
                           lefttreemax->right = root;
                           lefttreemax = root;
                   } else
                           break;
           }
           /* Assemble the new root. */
           lefttreemax->right = root->left;
           righttreemin->left = root->right;
           root->left = dummy.right;
           root->right = dummy.left;
           return (root);
   }
   
   /*
    *      vm_page_insert:         [ internal use only ]
    *
    *      Inserts the given mem entry into the object and object list.
    *
    *      The pagetables are not updated but will presumably fault the page
    *      in if necessary, or if a kernel page the caller will at some point
    *      enter the page into the kernel's pmap.  We are not allowed to block
    *      here so we *can't* do this anyway.
    *
    *      The object and page must be locked.
    *      This routine may not block.
    */
   void
   vm_page_insert(vm_page_t m, vm_object_t object, vm_pindex_t pindex)
   {
           vm_page_t root;
   
           VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
           if (m->object != NULL)
                   panic("vm_page_insert: page already inserted");
   
           /*
            * Record the object/offset pair in this page
            */
           m->object = object;
           m->pindex = pindex;
   
           /*
            * Now link into the object's ordered list of backed pages.
            */
           root = object->root;
           if (root == NULL) {
                   m->left = NULL;
                   m->right = NULL;
                   TAILQ_INSERT_TAIL(&object->memq, m, listq);
           } else {
                   root = vm_page_splay(pindex, root);
                   if (pindex < root->pindex) {
                           m->left = root->left;
                           m->right = root;
                           root->left = NULL;
                           TAILQ_INSERT_BEFORE(root, m, listq);
                   } else if (pindex == root->pindex)
                           panic("vm_page_insert: offset already allocated");
                   else {
                           m->right = root->right;
                           m->left = root;
                           root->right = NULL;
                           TAILQ_INSERT_AFTER(&object->memq, root, m, listq);
                   }
           }
           object->root = m;
           object->generation++;
   
           /*
            * show that the object has one more resident page.
            */
           object->resident_page_count++;
   
           /*
            * Since we are inserting a new and possibly dirty page,
            * update the object's OBJ_WRITEABLE and OBJ_MIGHTBEDIRTY flags.
            */
           if (m->flags & PG_WRITEABLE)
                   vm_object_set_writeable_dirty(object);
   }
   
   /*
    *      vm_page_remove:
    *                              NOTE: used by device pager as well -wfj
    *
    *      Removes the given mem entry from the object/offset-page
    *      table and the object page list, but do not invalidate/terminate
    *      the backing store.
    *
    *      The object and page must be locked.
    *      The underlying pmap entry (if any) is NOT removed here.
    *      This routine may not block.
    */
   void
   vm_page_remove(vm_page_t m)
   {
           vm_object_t object;
           vm_page_t root;
   
           mtx_assert(&vm_page_queue_mtx, MA_OWNED);
           if ((object = m->object) == NULL)
                   return;
           VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
           if (m->flags & PG_BUSY) {
                   vm_page_flag_clear(m, PG_BUSY);
                   vm_page_flash(m);
           }
   
           /*
            * Now remove from the object's list of backed pages.
            */
           if (m != object->root)
                   vm_page_splay(m->pindex, object->root);
           if (m->left == NULL)
                   root = m->right;
           else {
                   root = vm_page_splay(m->pindex, m->left);
                   root->right = m->right;
           }
           object->root = root;
           TAILQ_REMOVE(&object->memq, m, listq);
   
           /*
            * And show that the object has one fewer resident page.
            */
           object->resident_page_count--;
           object->generation++;
   
           m->object = NULL;
   }
   
   /*
    *      vm_page_lookup:
    *
    *      Returns the page associated with the object/offset
    *      pair specified; if none is found, NULL is returned.
    *
    *      The object must be locked.
    *      This routine may not block.
    *      This is a critical path routine
    */
   vm_page_t
   vm_page_lookup(vm_object_t object, vm_pindex_t pindex)
   {
           vm_page_t m;
   
           VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
           if ((m = object->root) != NULL && m->pindex != pindex) {
                   m = vm_page_splay(pindex, m);
                   if ((object->root = m)->pindex != pindex)
                           m = NULL;
           }
           return (m);
   }
   
   /*
    *      vm_page_rename:
    *
    *      Move the given memory entry from its
    *      current object to the specified target object/offset.
    *
    *      The object must be locked.
    *      This routine may not block.
    *
    *      Note: swap associated with the page must be invalidated by the move.  We
    *            have to do this for several reasons:  (1) we aren't freeing the
    *            page, (2) we are dirtying the page, (3) the VM system is probably
    *            moving the page from object A to B, and will then later move
    *            the backing store from A to B and we can't have a conflict.
    *
    *      Note: we *always* dirty the page.  It is necessary both for the
    *            fact that we moved it, and because we may be invalidating
    *            swap.  If the page is on the cache, we have to deactivate it
    *            or vm_page_dirty() will panic.  Dirty pages are not allowed
    *            on the cache.
    */
   void
   vm_page_rename(vm_page_t m, vm_object_t new_object, vm_pindex_t new_pindex)
   {
   
           vm_page_remove(m);
           vm_page_insert(m, new_object, new_pindex);
           if (m->queue - m->pc == PQ_CACHE)
                   vm_page_deactivate(m);
           vm_page_dirty(m);
   }
   
   /*
    *      vm_page_select_cache:
    *
    *      Move a page of the given color from the cache queue to the free
    *      queue.  As pages might be found, but are not applicable, they are
    *      deactivated.
    *
    *      This routine may not block.
    */
   vm_page_t
   vm_page_select_cache(int color)
   {
           vm_object_t object;
           vm_page_t m;
           boolean_t was_trylocked;
   
           mtx_assert(&vm_page_queue_mtx, MA_OWNED);
           while ((m = vm_pageq_find(PQ_CACHE, color, FALSE)) != NULL) {
                   KASSERT(m->dirty == 0, ("Found dirty cache page %p", m));
                   KASSERT(!pmap_page_is_mapped(m),
                       ("Found mapped cache page %p", m));
                   KASSERT((m->flags & PG_UNMANAGED) == 0,
                       ("Found unmanaged cache page %p", m));
                   KASSERT(m->wire_count == 0, ("Found wired cache page %p", m));
                   if (m->hold_count == 0 && (object = m->object,
                       (was_trylocked = VM_OBJECT_TRYLOCK(object)) ||
                       VM_OBJECT_LOCKED(object))) {
                           KASSERT((m->flags & PG_BUSY) == 0 && m->busy == 0,
                               ("Found busy cache page %p", m));
                           vm_page_free(m);
                           if (was_trylocked)
                                   VM_OBJECT_UNLOCK(object);
                           break;
                   }
                   vm_page_deactivate(m);
           }
           return (m);
   }
   
   /*
    *      vm_page_alloc:
    *
    *      Allocate and return a memory cell associated
    *      with this VM object/offset pair.
    *
    *      page_req classes:
    *      VM_ALLOC_NORMAL         normal process request
    *      VM_ALLOC_SYSTEM         system *really* needs a page
    *      VM_ALLOC_INTERRUPT      interrupt time request
    *      VM_ALLOC_ZERO           zero page
    *
    *      This routine may not block.
    *
    *      Additional special handling is required when called from an
    *      interrupt (VM_ALLOC_INTERRUPT).  We are not allowed to mess with
    *      the page cache in this case.
    */
   vm_page_t
   vm_page_alloc(vm_object_t object, vm_pindex_t pindex, int req)
   {
           vm_page_t m = NULL;
           int color, flags, page_req;
   
           page_req = req & VM_ALLOC_CLASS_MASK;
           KASSERT(curthread->td_intr_nesting_level == 0 ||
               page_req == VM_ALLOC_INTERRUPT,
               ("vm_page_alloc(NORMAL|SYSTEM) in interrupt context"));
   
           if ((req & VM_ALLOC_NOOBJ) == 0) {
                   KASSERT(object != NULL,
                       ("vm_page_alloc: NULL object."));
                   VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
                   color = (pindex + object->pg_color) & PQ_L2_MASK;
           } else
                   color = pindex & PQ_L2_MASK;
   
           /*
            * The pager is allowed to eat deeper into the free page list.
            */
           if ((curproc == pageproc) && (page_req != VM_ALLOC_INTERRUPT)) {
                   page_req = VM_ALLOC_SYSTEM;
           };
   
   loop:
           mtx_lock_spin(&vm_page_queue_free_mtx);
           if (cnt.v_free_count > cnt.v_free_reserved ||
               (page_req == VM_ALLOC_SYSTEM && 
                cnt.v_cache_count == 0 && 
                cnt.v_free_count > cnt.v_interrupt_free_min) ||
               (page_req == VM_ALLOC_INTERRUPT && cnt.v_free_count > 0)) {
                   /*
                    * Allocate from the free queue if the number of free pages
                    * exceeds the minimum for the request class.
                    */
                   m = vm_pageq_find(PQ_FREE, color, (req & VM_ALLOC_ZERO) != 0);
           } else if (page_req != VM_ALLOC_INTERRUPT) {
                   mtx_unlock_spin(&vm_page_queue_free_mtx);
                   /*
                    * Allocatable from cache (non-interrupt only).  On success,
                    * we must free the page and try again, thus ensuring that
                    * cnt.v_*_free_min counters are replenished.
                    */
                   vm_page_lock_queues();
                   if ((m = vm_page_select_cache(color)) == NULL) {
   #if defined(DIAGNOSTIC)
                           if (cnt.v_cache_count > 0)
                                   printf("vm_page_alloc(NORMAL): missing pages on cache queue: %d\n", cnt.v_cache_count);
   #endif
                           vm_page_unlock_queues();
                           atomic_add_int(&vm_pageout_deficit, 1);
                           pagedaemon_wakeup();
                           return (NULL);
                   }
                   vm_page_unlock_queues();
                   goto loop;
           } else {
                   /*
                    * Not allocatable from cache from interrupt, give up.
                    */
                   mtx_unlock_spin(&vm_page_queue_free_mtx);
                   atomic_add_int(&vm_pageout_deficit, 1);
                   pagedaemon_wakeup();
                   return (NULL);
           }
   
           /*
            *  At this point we had better have found a good page.
            */
   
           KASSERT(
               m != NULL,
               ("vm_page_alloc(): missing page on free queue")
           );
   
           /*
            * Remove from free queue
            */
           vm_pageq_remove_nowakeup(m);
   
           /*
            * Initialize structure.  Only the PG_ZERO flag is inherited.
            */
           flags = PG_BUSY;
           if (m->flags & PG_ZERO) {
                   vm_page_zero_count--;
                   if (req & VM_ALLOC_ZERO)
                           flags = PG_ZERO | PG_BUSY;
           }
           if (req & (VM_ALLOC_NOBUSY | VM_ALLOC_NOOBJ))
                   flags &= ~PG_BUSY;
           m->flags = flags;
           if (req & VM_ALLOC_WIRED) {
                   atomic_add_int(&cnt.v_wire_count, 1);
                   m->wire_count = 1;
           } else
                   m->wire_count = 0;
           m->hold_count = 0;
           m->act_count = 0;
           m->busy = 0;
           m->valid = 0;
           KASSERT(m->dirty == 0, ("vm_page_alloc: free/cache page %p was dirty", m));
           mtx_unlock_spin(&vm_page_queue_free_mtx);
   
           if ((req & VM_ALLOC_NOOBJ) == 0)
                   vm_page_insert(m, object, pindex);
           else
                   m->pindex = pindex;
   
           /*
            * Don't wakeup too often - wakeup the pageout daemon when
            * we would be nearly out of memory.
            */
           if (vm_paging_needed())
                   pagedaemon_wakeup();
   
           return (m);
   }
   
   /*
    *      vm_wait:        (also see VM_WAIT macro)
    *
    *      Block until free pages are available for allocation
    *      - Called in various places before memory allocations.
    */
   void
   vm_wait(void)
   {
   
           vm_page_lock_queues();
           if (curproc == pageproc) {
                   vm_pageout_pages_needed = 1;
                   msleep(&vm_pageout_pages_needed, &vm_page_queue_mtx,
                       PDROP | PSWP, "VMWait", 0);
           } else {
                   if (!vm_pages_needed) {
                           vm_pages_needed = 1;
                           wakeup(&vm_pages_needed);
                   }
                   msleep(&cnt.v_free_count, &vm_page_queue_mtx, PDROP | PVM,
                       "vmwait", 0);
           }
   }
   
   /*
    *      vm_waitpfault:  (also see VM_WAITPFAULT macro)
    *
    *      Block until free pages are available for allocation
    *      - Called only in vm_fault so that processes page faulting
    *        can be easily tracked.
    *      - Sleeps at a lower priority than vm_wait() so that vm_wait()ing
    *        processes will be able to grab memory first.  Do not change
    *        this balance without careful testing first.
    */
   void
   vm_waitpfault(void)
   {
   
           vm_page_lock_queues();
           if (!vm_pages_needed) {
                   vm_pages_needed = 1;
                   wakeup(&vm_pages_needed);
           }
           msleep(&cnt.v_free_count, &vm_page_queue_mtx, PDROP | PUSER,
               "pfault", 0);
   }
   
   /*
    *      vm_page_activate:
    *
    *      Put the specified page on the active list (if appropriate).
    *      Ensure that act_count is at least ACT_INIT but do not otherwise
    *      mess with it.
    *
    *      The page queues must be locked.
    *      This routine may not block.
    */
   void
   vm_page_activate(vm_page_t m)
   {
   
           mtx_assert(&vm_page_queue_mtx, MA_OWNED);
           if (m->queue != PQ_ACTIVE) {
                   if ((m->queue - m->pc) == PQ_CACHE)
                           cnt.v_reactivated++;
                   vm_pageq_remove(m);
                   if (m->wire_count == 0 && (m->flags & PG_UNMANAGED) == 0) {
                           if (m->act_count < ACT_INIT)
                                   m->act_count = ACT_INIT;
                           vm_pageq_enqueue(PQ_ACTIVE, m);
                   }
           } else {
                   if (m->act_count < ACT_INIT)
                           m->act_count = ACT_INIT;
           }
   }
   
   /*
    *      vm_page_free_wakeup:
    *
    *      Helper routine for vm_page_free_toq() and vm_page_cache().  This
    *      routine is called when a page has been added to the cache or free
    *      queues.
    *
    *      The page queues must be locked.
    *      This routine may not block.
    */
   static __inline void
   vm_page_free_wakeup(void)
   {
   
           mtx_assert(&vm_page_queue_mtx, MA_OWNED);
           /*
            * if pageout daemon needs pages, then tell it that there are
            * some free.
            */
           if (vm_pageout_pages_needed &&
               cnt.v_cache_count + cnt.v_free_count >= cnt.v_pageout_free_min) {
                   wakeup(&vm_pageout_pages_needed);
                   vm_pageout_pages_needed = 0;
           }
           /*
            * wakeup processes that are waiting on memory if we hit a
            * high water mark. And wakeup scheduler process if we have
            * lots of memory. this process will swapin processes.
            */
           if (vm_pages_needed && !vm_page_count_min()) {
                   vm_pages_needed = 0;
                   wakeup(&cnt.v_free_count);
           }
   }
   
   /*
    *      vm_page_free_toq:
    *
    *      Returns the given page to the PQ_FREE list,
    *      disassociating it with any VM object.
    *
    *      Object and page must be locked prior to entry.
    *      This routine may not block.
    */
   
   void
   vm_page_free_toq(vm_page_t m)
   {
           struct vpgqueues *pq;
           vm_object_t object = m->object;
   
          mtx_assert(&vm_page_queue_mtx, MA_OWNED);
          cnt.v_tfree++;
  
          if (m->busy || ((m->queue - m->pc) == PQ_FREE)) {
                  printf(
                  "vm_page_free: pindex(%lu), busy(%d), PG_BUSY(%d), hold(%d)\n",
                      (u_long)m->pindex, m->busy, (m->flags & PG_BUSY) ? 1 : 0,
                      m->hold_count);
                  if ((m->queue - m->pc) == PQ_FREE)
                          panic("vm_page_free: freeing free page");
                  else
                          panic("vm_page_free: freeing busy page");
          }
  
          /*
           * unqueue, then remove page.  Note that we cannot destroy
           * the page here because we do not want to call the pager's
           * callback routine until after we've put the page on the
           * appropriate free queue.
           */
          vm_pageq_remove_nowakeup(m);
          vm_page_remove(m);
  
          /*
           * If fictitious remove object association and
           * return, otherwise delay object association removal.
           */
          if ((m->flags & PG_FICTITIOUS) != 0) {
                  return;
          }
  
          m->valid = 0;
          vm_page_undirty(m);
  
          if (m->wire_count != 0) {
                  if (m->wire_count > 1) {
                          panic("vm_page_free: invalid wire count (%d), pindex: 0x%lx",
                                  m->wire_count, (long)m->pindex);
                  }
                  panic("vm_page_free: freeing wired page");
          }
  
          /*
           * If we've exhausted the object's resident pages we want to free
           * it up.
           */
          if (object && 
              (object->type == OBJT_VNODE) &&
              ((object->flags & OBJ_DEAD) == 0)
          ) {
                  struct vnode *vp = (struct vnode *)object->handle;
  
                  if (vp) {
                          VI_LOCK(vp);
                          if (VSHOULDFREE(vp))
                                  vfree(vp);
                          VI_UNLOCK(vp);
                  }
          }
  
          /*
           * Clear the UNMANAGED flag when freeing an unmanaged page.
           */
          if (m->flags & PG_UNMANAGED) {
                  m->flags &= ~PG_UNMANAGED;
          }
  
          if (m->hold_count != 0) {
                  m->flags &= ~PG_ZERO;
                  m->queue = PQ_HOLD;
          } else
                  m->queue = PQ_FREE + m->pc;
          pq = &vm_page_queues[m->queue];
          mtx_lock_spin(&vm_page_queue_free_mtx);
          pq->lcnt++;
          ++(*pq->cnt);
  
          /*
           * Put zero'd pages on the end ( where we look for zero'd pages
           * first ) and non-zerod pages at the head.
           */
          if (m->flags & PG_ZERO) {
                  TAILQ_INSERT_TAIL(&pq->pl, m, pageq);
                  ++vm_page_zero_count;
          } else {
                  TAILQ_INSERT_HEAD(&pq->pl, m, pageq);
          }
          mtx_unlock_spin(&vm_page_queue_free_mtx);
          vm_page_free_wakeup();
  }
  
  /*
   *      vm_page_unmanage:
   *
   *      Prevent PV management from being done on the page.  The page is
   *      removed from the paging queues as if it were wired, and as a 
   *      consequence of no longer being managed the pageout daemon will not
   *      touch it (since there is no way to locate the pte mappings for the
   *      page).  madvise() calls that mess with the pmap will also no longer
   *      operate on the page.
   *
   *      Beyond that the page is still reasonably 'normal'.  Freeing the page
   *      will clear the flag.
   *
   *      This routine is used by OBJT_PHYS objects - objects using unswappable
   *      physical memory as backing store rather then swap-backed memory and
   *      will eventually be extended to support 4MB unmanaged physical 
   *      mappings.
   */
  void
  vm_page_unmanage(vm_page_t m)
  {
  
          mtx_assert(&vm_page_queue_mtx, MA_OWNED);
          if ((m->flags & PG_UNMANAGED) == 0) {
                  if (m->wire_count == 0)
                          vm_pageq_remove(m);
          }
          vm_page_flag_set(m, PG_UNMANAGED);
  }
  
  /*
   *      vm_page_wire:
   *
   *      Mark this page as wired down by yet
   *      another map, removing it from paging queues
   *      as necessary.
   *
   *      The page queues must be locked.
   *      This routine may not block.
   */
  void
  vm_page_wire(vm_page_t m)
  {
  
          /*
           * Only bump the wire statistics if the page is not already wired,
           * and only unqueue the page if it is on some queue (if it is unmanaged
           * it is already off the queues).
           */
          mtx_assert(&vm_page_queue_mtx, MA_OWNED);
          if (m->flags & PG_FICTITIOUS)
                  return;
          if (m->wire_count == 0) {
                  if ((m->flags & PG_UNMANAGED) == 0)
                          vm_pageq_remove(m);
                  atomic_add_int(&cnt.v_wire_count, 1);
          }
          m->wire_count++;
          KASSERT(m->wire_count != 0, ("vm_page_wire: wire_count overflow m=%p", m));
  }
  
  /*
   *      vm_page_unwire:
   *
   *      Release one wiring of this page, potentially
   *      enabling it to be paged again.
   *
   *      Many pages placed on the inactive queue should actually go
   *      into the cache, but it is difficult to figure out which.  What
   *      we do instead, if the inactive target is well met, is to put
   *      clean pages at the head of the inactive queue instead of the tail.
   *      This will cause them to be moved to the cache more quickly and
   *      if not actively re-referenced, freed more quickly.  If we just
   *      stick these pages at the end of the inactive queue, heavy filesystem
   *      meta-data accesses can cause an unnecessary paging load on memory bound 
   *      processes.  This optimization causes one-time-use metadata to be
   *      reused more quickly.
   *
   *      BUT, if we are in a low-memory situation we have no choice but to
   *      put clean pages on the cache queue.
   *
   *      A number of routines use vm_page_unwire() to guarantee that the page
   *      will go into either the inactive or active queues, and will NEVER
   *      be placed in the cache - for example, just after dirtying a page.
   *      dirty pages in the cache are not allowed.
   *
   *      The page queues must be locked.
   *      This routine may not block.
   */
  void
  vm_page_unwire(vm_page_t m, int activate)
  {
  
          mtx_assert(&vm_page_queue_mtx, MA_OWNED);
          if (m->flags & PG_FICTITIOUS)
                  return;
          if (m->wire_count > 0) {
                  m->wire_count--;
                  if (m->wire_count == 0) {
                          atomic_subtract_int(&cnt.v_wire_count, 1);
                          if (m->flags & PG_UNMANAGED) {
                                  ;
                          } else if (activate)
                                  vm_pageq_enqueue(PQ_ACTIVE, m);
                          else {
                                  vm_page_flag_clear(m, PG_WINATCFLS);
                                  vm_pageq_enqueue(PQ_INACTIVE, m);
                          }
                  }
          } else {
                  panic("vm_page_unwire: invalid wire count: %d", m->wire_count);
          }
  }
  
  
  /*
   * Move the specified page to the inactive queue.  If the page has
   * any associated swap, the swap is deallocated.
   *
   * Normally athead is 0 resulting in LRU operation.  athead is set
   * to 1 if we want this page to be 'as if it were placed in the cache',
   * except without unmapping it from the process address space.
   *
   * This routine may not block.
   */
  static __inline void
  _vm_page_deactivate(vm_page_t m, int athead)
  {
  
          mtx_assert(&vm_page_queue_mtx, MA_OWNED);
  
          /*
           * Ignore if already inactive.
           */
          if (m->queue == PQ_INACTIVE)
                  return;
          if (m->wire_count == 0 && (m->flags & PG_UNMANAGED) == 0) {
                  if ((m->queue - m->pc) == PQ_CACHE)
                          cnt.v_reactivated++;
                  vm_page_flag_clear(m, PG_WINATCFLS);
                  vm_pageq_remove(m);
                  if (athead)
                          TAILQ_INSERT_HEAD(&vm_page_queues[PQ_INACTIVE].pl, m, pageq);
                  else
                          TAILQ_INSERT_TAIL(&vm_page_queues[PQ_INACTIVE].pl, m, pageq);
                  m->queue = PQ_INACTIVE;
                  vm_page_queues[PQ_INACTIVE].lcnt++;
                  cnt.v_inactive_count++;
          }
  }
  
  void
  vm_page_deactivate(vm_page_t m)
  {
      _vm_page_deactivate(m, 0);
  }
  
  /*
   * vm_page_try_to_cache:
   *
   * Returns 0 on failure, 1 on success
   */
  int
  vm_page_try_to_cache(vm_page_t m)
  {
  
          mtx_assert(&vm_page_queue_mtx, MA_OWNED);
          VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
          if (m->dirty || m->hold_count || m->busy || m->wire_count ||
              (m->flags & (PG_BUSY|PG_UNMANAGED))) {
                  return (0);
          }
          pmap_remove_all(m);
          if (m->dirty)
                  return (0);
          vm_page_cache(m);
          return (1);
  }
  
  /*
   * vm_page_try_to_free()
   *
   *      Attempt to free the page.  If we cannot free it, we do nothing.
   *      1 is returned on success, 0 on failure.
   */
  int
  vm_page_try_to_free(vm_page_t m)
  {
  
          mtx_assert(&vm_page_queue_mtx, MA_OWNED);
          if (m->object != NULL)
                  VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
          if (m->dirty || m->hold_count || m->busy || m->wire_count ||
              (m->flags & (PG_BUSY|PG_UNMANAGED))) {
                  return (0);
          }
          pmap_remove_all(m);
          if (m->dirty)
                  return (0);
          vm_page_free(m);
          return (1);
  }
  
  /*
   * vm_page_cache
   *
   * Put the specified page onto the page cache queue (if appropriate).
   *
   * This routine may not block.
   */
  void
  vm_page_cache(vm_page_t m)
  {
  
          mtx_assert(&vm_page_queue_mtx, MA_OWNED);
          VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
          if ((m->flags & (PG_BUSY|PG_UNMANAGED)) || m->busy ||
              m->hold_count || m->wire_count) {
                  printf("vm_page_cache: attempting to cache busy page\n");
                  return;
          }
          if ((m->queue - m->pc) == PQ_CACHE)
                  return;
  
          /*
           * Remove all pmaps and indicate that the page is not
           * writeable or mapped.
           */
          pmap_remove_all(m);
          if (m->dirty != 0) {
                  panic("vm_page_cache: caching a dirty page, pindex: %ld",
                          (long)m->pindex);
          }
          vm_pageq_remove_nowakeup(m);
          vm_pageq_enqueue(PQ_CACHE + m->pc, m);
          vm_page_free_wakeup();
  }
  
  /*
   * vm_page_dontneed
   *
   *      Cache, deactivate, or do nothing as appropriate.  This routine
   *      is typically used by madvise() MADV_DONTNEED.
   *
   *      Generally speaking we want to move the page into the cache so
   *      it gets reused quickly.  However, this can result in a silly syndrome
   *      due to the page recycling too quickly.  Small objects will not be
   *      fully cached.  On the otherhand, if we move the page to the inactive
   *      queue we wind up with a problem whereby very large objects 
   *      unnecessarily blow away our inactive and cache queues.
   *
   *      The solution is to move the pages based on a fixed weighting.  We
   *      either leave them alone, deactivate them, or move them to the cache,
   *      where moving them to the cache has the highest weighting.
   *      By forcing some pages into other queues we eventually force the
   *      system to balance the queues, potentially recovering other unrelated
   *      space from active.  The idea is to not force this to happen too
   *      often.
   */
  void
  vm_page_dontneed(vm_page_t m)
  {
          static int dnweight;
          int dnw;
          int head;
  
          mtx_assert(&vm_page_queue_mtx, MA_OWNED);
          dnw = ++dnweight;
  
          /*
           * occassionally leave the page alone
           */
          if ((dnw & 0x01F0) == 0 ||
              m->queue == PQ_INACTIVE || 
              m->queue - m->pc == PQ_CACHE
          ) {
                  if (m->act_count >= ACT_INIT)
                          --m->act_count;
                  return;
          }
  
          if (m->dirty == 0 && pmap_is_modified(m))
                  vm_page_dirty(m);
  
          if (m->dirty || (dnw & 0x0070) == 0) {
                  /*
                   * Deactivate the page 3 times out of 32.
                   */
                  head = 0;
          } else {
                  /*
                   * Cache the page 28 times out of every 32.  Note that
                   * the page is deactivated instead of cached, but placed
                   * at the head of the queue instead of the tail.
                   */
                  head = 1;
          }
          _vm_page_deactivate(m, head);
  }
  
  /*
   * Grab a page, waiting until we are waken up due to the page
   * changing state.  We keep on waiting, if the page continues
   * to be in the object.  If the page doesn't exist, first allocate it
   * and then conditionally zero it.
   *
   * This routine may block.
   */
  vm_page_t
  vm_page_grab(vm_object_t object, vm_pindex_t pindex, int allocflags)
  {
          vm_page_t m;
  
          VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  retrylookup:
          if ((m = vm_page_lookup(object, pindex)) != NULL) {
                  vm_page_lock_queues();
                  if (m->busy || (m->flags & PG_BUSY)) {
                          vm_page_flag_set(m, PG_WANTED | PG_REFERENCED);
                          VM_OBJECT_UNLOCK(object);
                          msleep(m, &vm_page_queue_mtx, PDROP | PVM, "pgrbwt", 0);
                          VM_OBJECT_LOCK(object);
                          if ((allocflags & VM_ALLOC_RETRY) == 0)
                                  return (NULL);
                          goto retrylookup;
                  } else {
                          if (allocflags & VM_ALLOC_WIRED)
                                  vm_page_wire(m);
                          if ((allocflags & VM_ALLOC_NOBUSY) == 0)
                                  vm_page_busy(m);
                          vm_page_unlock_queues();
                          return (m);
                  }
          }
          m = vm_page_alloc(object, pindex, allocflags & ~VM_ALLOC_RETRY);
          if (m == NULL) {
                  VM_OBJECT_UNLOCK(object);
                  VM_WAIT;
                  VM_OBJECT_LOCK(object);
                  if ((allocflags & VM_ALLOC_RETRY) == 0)
                          return (NULL);
                  goto retrylookup;
          }
          if (allocflags & VM_ALLOC_ZERO && (m->flags & PG_ZERO) == 0)
                  pmap_zero_page(m);
          return (m);
  }
  
  /*
   * Mapping function for valid bits or for dirty bits in
   * a page.  May not block.
   *
   * Inputs are required to range within a page.
   */
  __inline int
  vm_page_bits(int base, int size)
  {
          int first_bit;
          int last_bit;
  
          KASSERT(
              base + size <= PAGE_SIZE,
              ("vm_page_bits: illegal base/size %d/%d", base, size)
          );
  
          if (size == 0)          /* handle degenerate case */
                  return (0);
  
          first_bit = base >> DEV_BSHIFT;
          last_bit = (base + size - 1) >> DEV_BSHIFT;
  
          return ((2 << last_bit) - (1 << first_bit));
  }
  
  /*
   *      vm_page_set_validclean:
   *
   *      Sets portions of a page valid and clean.  The arguments are expected
   *      to be DEV_BSIZE aligned but if they aren't the bitmap is inclusive
   *      of any partial chunks touched by the range.  The invalid portion of
   *      such chunks will be zero'd.
   *
   *      This routine may not block.
   *
   *      (base + size) must be less then or equal to PAGE_SIZE.
   */
  void
  vm_page_set_validclean(vm_page_t m, int base, int size)
  {
          int pagebits;
          int frag;
          int endoff;
  
          mtx_assert(&vm_page_queue_mtx, MA_OWNED);
          VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
          if (size == 0)  /* handle degenerate case */
                  return;
  
          /*
           * If the base is not DEV_BSIZE aligned and the valid
           * bit is clear, we have to zero out a portion of the
           * first block.
           */
          if ((frag = base & ~(DEV_BSIZE - 1)) != base &&
              (m->valid & (1 << (base >> DEV_BSHIFT))) == 0)
                  pmap_zero_page_area(m, frag, base - frag);
  
          /*
           * If the ending offset is not DEV_BSIZE aligned and the 
           * valid bit is clear, we have to zero out a portion of
           * the last block.
           */
          endoff = base + size;
          if ((frag = endoff & ~(DEV_BSIZE - 1)) != endoff &&
              (m->valid & (1 << (endoff >> DEV_BSHIFT))) == 0)
                  pmap_zero_page_area(m, endoff,
                      DEV_BSIZE - (endoff & (DEV_BSIZE - 1)));
  
          /*
           * Set valid, clear dirty bits.  If validating the entire
           * page we can safely clear the pmap modify bit.  We also
           * use this opportunity to clear the PG_NOSYNC flag.  If a process
           * takes a write fault on a MAP_NOSYNC memory area the flag will
           * be set again.
           *
           * We set valid bits inclusive of any overlap, but we can only
           * clear dirty bits for DEV_BSIZE chunks that are fully within
           * the range.
           */
          pagebits = vm_page_bits(base, size);
          m->valid |= pagebits;
  #if 0   /* NOT YET */
          if ((frag = base & (DEV_BSIZE - 1)) != 0) {
                  frag = DEV_BSIZE - frag;
                  base += frag;
                  size -= frag;
                  if (size < 0)
                          size = 0;
          }
          pagebits = vm_page_bits(base, size & (DEV_BSIZE - 1));
  #endif
          m->dirty &= ~pagebits;
          if (base == 0 && size == PAGE_SIZE) {
                  pmap_clear_modify(m);
                  vm_page_flag_clear(m, PG_NOSYNC);
          }
  }
  
  void
  vm_page_clear_dirty(vm_page_t m, int base, int size)
  {
  
          mtx_assert(&vm_page_queue_mtx, MA_OWNED);
          m->dirty &= ~vm_page_bits(base, size);
  }
  
  /*
   *      vm_page_set_invalid:
   *
   *      Invalidates DEV_BSIZE'd chunks within a page.  Both the
   *      valid and dirty bits for the effected areas are cleared.
   *
   *      May not block.
   */
  void
  vm_page_set_invalid(vm_page_t m, int base, int size)
  {
          int bits;
  
          VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
          bits = vm_page_bits(base, size);
          mtx_assert(&vm_page_queue_mtx, MA_OWNED);
          m->valid &= ~bits;
          m->dirty &= ~bits;
          m->object->generation++;
  }
  
  /*
   * vm_page_zero_invalid()
   *
   *      The kernel assumes that the invalid portions of a page contain 
   *      garbage, but such pages can be mapped into memory by user code.
   *      When this occurs, we must zero out the non-valid portions of the
   *      page so user code sees what it expects.
   *
   *      Pages are most often semi-valid when the end of a file is mapped 
   *      into memory and the file's size is not page aligned.
   */
  void
  vm_page_zero_invalid(vm_page_t m, boolean_t setvalid)
  {
          int b;
          int i;
  
          VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
          /*
           * Scan the valid bits looking for invalid sections that
           * must be zerod.  Invalid sub-DEV_BSIZE'd areas ( where the
           * valid bit may be set ) have already been zerod by
           * vm_page_set_validclean().
           */
          for (b = i = 0; i <= PAGE_SIZE / DEV_BSIZE; ++i) {
                  if (i == (PAGE_SIZE / DEV_BSIZE) || 
                      (m->valid & (1 << i))
                  ) {
                          if (i > b) {
                                  pmap_zero_page_area(m, 
                                      b << DEV_BSHIFT, (i - b) << DEV_BSHIFT);
                          }
                          b = i + 1;
                  }
          }
  
          /*
           * setvalid is TRUE when we can safely set the zero'd areas
           * as being valid.  We can do this if there are no cache consistancy
           * issues.  e.g. it is ok to do with UFS, but not ok to do with NFS.
           */
          if (setvalid)
                  m->valid = VM_PAGE_BITS_ALL;
  }
  
  /*
   *      vm_page_is_valid:
   *
   *      Is (partial) page valid?  Note that the case where size == 0
   *      will return FALSE in the degenerate case where the page is
   *      entirely invalid, and TRUE otherwise.
   *
   *      May not block.
   */
  int
  vm_page_is_valid(vm_page_t m, int base, int size)
  {
          int bits = vm_page_bits(base, size);
  
          VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
          if (m->valid && ((m->valid & bits) == bits))
                  return 1;
          else
                  return 0;
  }
  
  /*
   * update dirty bits from pmap/mmu.  May not block.
   */
  void
  vm_page_test_dirty(vm_page_t m)
  {
          if ((m->dirty != VM_PAGE_BITS_ALL) && pmap_is_modified(m)) {
                  vm_page_dirty(m);
          }
  }
  
  int so_zerocp_fullpage = 0;
  
  void
  vm_page_cowfault(vm_page_t m)
  {
          vm_page_t mnew;
          vm_object_t object;
          vm_pindex_t pindex;
  
          object = m->object;
          pindex = m->pindex;
  
   retry_alloc:
          vm_page_remove(m);
          mnew = vm_page_alloc(object, pindex, VM_ALLOC_NORMAL);
          if (mnew == NULL) {
                  vm_page_insert(m, object, pindex);
                  vm_page_unlock_queues();
                  VM_OBJECT_UNLOCK(object);
                  VM_WAIT;
                  VM_OBJECT_LOCK(object);
                  vm_page_lock_queues();
                  goto retry_alloc;
          }
  
          if (m->cow == 0) {
                  /* 
                   * check to see if we raced with an xmit complete when 
                   * waiting to allocate a page.  If so, put things back 
                   * the way they were 
                   */
                  vm_page_free(mnew);
                  vm_page_insert(m, object, pindex);
          } else { /* clear COW & copy page */
                  if (!so_zerocp_fullpage)
                          pmap_copy_page(m, mnew);
                  mnew->valid = VM_PAGE_BITS_ALL;
                  vm_page_dirty(mnew);
                  vm_page_flag_clear(mnew, PG_BUSY);
          }
  }
  
  void 
  vm_page_cowclear(vm_page_t m)
  {
  
          mtx_assert(&vm_page_queue_mtx, MA_OWNED);
          if (m->cow) {
                  m->cow--;
                  /* 
                   * let vm_fault add back write permission  lazily
                   */
          } 
          /*
           *  sf_buf_free() will free the page, so we needn't do it here
           */ 
  }
  
  void
  vm_page_cowsetup(vm_page_t m)
  {
  
          mtx_assert(&vm_page_queue_mtx, MA_OWNED);
          m->cow++;
          pmap_page_protect(m, VM_PROT_READ);
  }
  
  #include "opt_ddb.h"
  #ifdef DDB
  #include <sys/kernel.h>
  
  #include <ddb/ddb.h>
  
  DB_SHOW_COMMAND(page, vm_page_print_page_info)
  {
          db_printf("cnt.v_free_count: %d\n", cnt.v_free_count);
          db_printf("cnt.v_cache_count: %d\n", cnt.v_cache_count);
          db_printf("cnt.v_inactive_count: %d\n", cnt.v_inactive_count);
          db_printf("cnt.v_active_count: %d\n", cnt.v_active_count);
          db_printf("cnt.v_wire_count: %d\n", cnt.v_wire_count);
          db_printf("cnt.v_free_reserved: %d\n", cnt.v_free_reserved);
          db_printf("cnt.v_free_min: %d\n", cnt.v_free_min);
          db_printf("cnt.v_free_target: %d\n", cnt.v_free_target);
          db_printf("cnt.v_cache_min: %d\n", cnt.v_cache_min);
          db_printf("cnt.v_inactive_target: %d\n", cnt.v_inactive_target);
  }
  
  DB_SHOW_COMMAND(pageq, vm_page_print_pageq_info)
  {
          int i;
          db_printf("PQ_FREE:");
          for (i = 0; i < PQ_L2_SIZE; i++) {
                  db_printf(" %d", vm_page_queues[PQ_FREE + i].lcnt);
          }
          db_printf("\n");
                  
          db_printf("PQ_CACHE:");
          for (i = 0; i < PQ_L2_SIZE; i++) {
                  db_printf(" %d", vm_page_queues[PQ_CACHE + i].lcnt);
          }
          db_printf("\n");
  
          db_printf("PQ_ACTIVE: %d, PQ_INACTIVE: %d\n",
                  vm_page_queues[PQ_ACTIVE].lcnt,
                  vm_page_queues[PQ_INACTIVE].lcnt);
  }
  #endif /* DDB */

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