FreeBSD/Linux Kernel Cross Reference
sys/uvm/uvm_amap.c

     /*      $NetBSD: uvm_amap.c,v 1.126 2021/03/13 15:29:55 skrll Exp $     */
     
     /*
      * Copyright (c) 1997 Charles D. Cranor and Washington University.
      * All rights reserved.
      *
      * 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.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
     */
    
    /*
     * uvm_amap.c: amap operations
     */
    
    /*
     * this file contains functions that perform operations on amaps.  see
     * uvm_amap.h for a brief explanation of the role of amaps in uvm.
     */
    
    #include <sys/cdefs.h>
    __KERNEL_RCSID(0, "$NetBSD: uvm_amap.c,v 1.126 2021/03/13 15:29:55 skrll Exp $");
    
    #include "opt_uvmhist.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/kmem.h>
    #include <sys/pool.h>
    #include <sys/atomic.h>
    
    #include <uvm/uvm.h>
    #include <uvm/uvm_swap.h>
    
    /*
     * cache for allocation of vm_map structures.  note that in order to
     * avoid an endless loop, the amap cache's allocator cannot allocate
     * memory from an amap (it currently goes through the kernel uobj, so
     * we are ok).
     */
    static struct pool_cache uvm_amap_cache;
    static kmutex_t amap_list_lock __cacheline_aligned;
    static LIST_HEAD(, vm_amap) amap_list;
    
    /*
     * local functions
     */
    
    static int
    amap_roundup_slots(int slots)
    {
    
            return kmem_roundup_size(slots * sizeof(int)) / sizeof(int);
    }
    
    #ifdef UVM_AMAP_PPREF
    /*
     * what is ppref?   ppref is an _optional_ amap feature which is used
     * to keep track of reference counts on a per-page basis.  it is enabled
     * when UVM_AMAP_PPREF is defined.
     *
     * when enabled, an array of ints is allocated for the pprefs.  this
     * array is allocated only when a partial reference is added to the
     * map (either by unmapping part of the amap, or gaining a reference
     * to only a part of an amap).  if the allocation of the array fails
     * (KM_NOSLEEP), then we set the array pointer to PPREF_NONE to indicate
     * that we tried to do ppref's but couldn't alloc the array so just
     * give up (after all, this is an optional feature!).
     *
     * the array is divided into page sized "chunks."   for chunks of length 1,
     * the chunk reference count plus one is stored in that chunk's slot.
     * for chunks of length > 1 the first slot contains (the reference count
     * plus one) * -1.    [the negative value indicates that the length is
     * greater than one.]   the second slot of the chunk contains the length
     * of the chunk.   here is an example:
     *
     * actual REFS:  2  2  2  2  3  1  1  0  0  0  4  4  0  1  1  1
     *       ppref: -3  4  x  x  4 -2  2 -1  3  x -5  2  1 -2  3  x
     *              <----------><-><----><-------><----><-><------->
     * (x = don't care)
     *
     * this allows us to allow one int to contain the ref count for the whole
    * chunk.    note that the "plus one" part is needed because a reference
    * count of zero is neither positive or negative (need a way to tell
    * if we've got one zero or a bunch of them).
    *
    * here are some in-line functions to help us.
    */
   
   /*
    * pp_getreflen: get the reference and length for a specific offset
    *
    * => ppref's amap must be locked
    */
   static inline void
   pp_getreflen(int *ppref, int offset, int *refp, int *lenp)
   {
   
           if (ppref[offset] > 0) {                /* chunk size must be 1 */
                   *refp = ppref[offset] - 1;      /* don't forget to adjust */
                   *lenp = 1;
           } else {
                   *refp = (ppref[offset] * -1) - 1;
                   *lenp = ppref[offset+1];
           }
   }
   
   /*
    * pp_setreflen: set the reference and length for a specific offset
    *
    * => ppref's amap must be locked
    */
   static inline void
   pp_setreflen(int *ppref, int offset, int ref, int len)
   {
           if (len == 0)
                   return;
           if (len == 1) {
                   ppref[offset] = ref + 1;
           } else {
                   ppref[offset] = (ref + 1) * -1;
                   ppref[offset+1] = len;
           }
   }
   #endif /* UVM_AMAP_PPREF */
   
   /*
    * amap_alloc1: allocate an amap, but do not initialise the overlay.
    *
    * => Note: lock is not set.
    */
   static struct vm_amap *
   amap_alloc1(int slots, int padslots, int flags)
   {
           const bool nowait = (flags & UVM_FLAG_NOWAIT) != 0;
           const km_flag_t kmflags = nowait ? KM_NOSLEEP : KM_SLEEP;
           struct vm_amap *amap;
           krwlock_t *newlock, *oldlock;
           int totalslots;
   
           amap = pool_cache_get(&uvm_amap_cache, nowait ? PR_NOWAIT : PR_WAITOK);
           if (amap == NULL) {
                   return NULL;
           }
           KASSERT(amap->am_lock != NULL);
           KASSERT(amap->am_nused == 0);
   
           /* Try to privatize the lock if currently shared. */
           if (rw_obj_refcnt(amap->am_lock) > 1) {
                   newlock = rw_obj_tryalloc();
                   if (newlock != NULL) {
                           oldlock = amap->am_lock;
                           mutex_enter(&amap_list_lock);
                           amap->am_lock = newlock;
                           mutex_exit(&amap_list_lock);
                           rw_obj_free(oldlock);
                   }
           }
   
           totalslots = amap_roundup_slots(slots + padslots);
           amap->am_ref = 1;
           amap->am_flags = 0;
   #ifdef UVM_AMAP_PPREF
           amap->am_ppref = NULL;
   #endif
           amap->am_maxslot = totalslots;
           amap->am_nslot = slots;
   
           /*
            * Note: since allocations are likely big, we expect to reduce the
            * memory fragmentation by allocating them in separate blocks.
            */
           amap->am_slots = kmem_alloc(totalslots * sizeof(int), kmflags);
           if (amap->am_slots == NULL)
                   goto fail1;
   
           amap->am_bckptr = kmem_alloc(totalslots * sizeof(int), kmflags);
           if (amap->am_bckptr == NULL)
                   goto fail2;
   
           amap->am_anon = kmem_alloc(totalslots * sizeof(struct vm_anon *),
               kmflags);
           if (amap->am_anon == NULL)
                   goto fail3;
   
           return amap;
   
   fail3:
           kmem_free(amap->am_bckptr, totalslots * sizeof(int));
   fail2:
           kmem_free(amap->am_slots, totalslots * sizeof(int));
   fail1:
           pool_cache_put(&uvm_amap_cache, amap);
   
           /*
            * XXX hack to tell the pagedaemon how many pages we need,
            * since we can need more than it would normally free.
            */
           if (nowait) {
                   extern u_int uvm_extrapages;
                   atomic_add_int(&uvm_extrapages,
                       ((sizeof(int) * 2 + sizeof(struct vm_anon *)) *
                       totalslots) >> PAGE_SHIFT);
           }
           return NULL;
   }
   
   /*
    * amap_alloc: allocate an amap to manage "sz" bytes of anonymous VM
    *
    * => caller should ensure sz is a multiple of PAGE_SIZE
    * => reference count to new amap is set to one
    * => new amap is returned unlocked
    */
   
   struct vm_amap *
   amap_alloc(vaddr_t sz, vaddr_t padsz, int waitf)
   {
           struct vm_amap *amap;
           int slots, padslots;
           UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);
   
           AMAP_B2SLOT(slots, sz);
           AMAP_B2SLOT(padslots, padsz);
   
           amap = amap_alloc1(slots, padslots, waitf);
           if (amap) {
                   memset(amap->am_anon, 0,
                       amap->am_maxslot * sizeof(struct vm_anon *));
           }
   
           UVMHIST_LOG(maphist,"<- done, amap = %#jx, sz=%jd", (uintptr_t)amap,
               sz, 0, 0);
           return(amap);
   }
   
   /*
    * amap_ctor: pool_cache constructor for new amaps
    *
    * => carefully synchronize with amap_swap_off()
    */
   static int
   amap_ctor(void *arg, void *obj, int flags)
   {
           struct vm_amap *amap = obj;
   
           if ((flags & PR_NOWAIT) != 0) {
                   amap->am_lock = rw_obj_tryalloc();
                   if (amap->am_lock == NULL) {
                           return ENOMEM;
                   }
           } else {
                   amap->am_lock = rw_obj_alloc();
           }
           amap->am_nused = 0;
           amap->am_flags = 0;
   
           mutex_enter(&amap_list_lock);
           LIST_INSERT_HEAD(&amap_list, amap, am_list);
           mutex_exit(&amap_list_lock);
           return 0;
   }
   
   /*
    * amap_ctor: pool_cache destructor for amaps
    *
    * => carefully synchronize with amap_swap_off()
    */
   static void
   amap_dtor(void *arg, void *obj)
   {
           struct vm_amap *amap = obj;
   
           KASSERT(amap->am_nused == 0);
   
           mutex_enter(&amap_list_lock);
           LIST_REMOVE(amap, am_list);
           mutex_exit(&amap_list_lock);
           rw_obj_free(amap->am_lock);
   }
   
   /*
    * uvm_amap_init: initialize the amap system.
    */
   void
   uvm_amap_init(void)
   {
   
           mutex_init(&amap_list_lock, MUTEX_DEFAULT, IPL_NONE);
   
           pool_cache_bootstrap(&uvm_amap_cache, sizeof(struct vm_amap), 0, 0,
               PR_LARGECACHE, "amappl", NULL, IPL_NONE, amap_ctor, amap_dtor,
               NULL);
   }
   
   /*
    * amap_free: free an amap
    *
    * => the amap must be unlocked
    * => the amap should have a zero reference count and be empty
    */
   void
   amap_free(struct vm_amap *amap)
   {
           int slots;
   
           UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);
   
           KASSERT(amap->am_ref == 0 && amap->am_nused == 0);
           KASSERT((amap->am_flags & AMAP_SWAPOFF) == 0);
           slots = amap->am_maxslot;
           kmem_free(amap->am_slots, slots * sizeof(*amap->am_slots));
           kmem_free(amap->am_bckptr, slots * sizeof(*amap->am_bckptr));
           kmem_free(amap->am_anon, slots * sizeof(*amap->am_anon));
   #ifdef UVM_AMAP_PPREF
           if (amap->am_ppref && amap->am_ppref != PPREF_NONE)
                   kmem_free(amap->am_ppref, slots * sizeof(*amap->am_ppref));
   #endif
           pool_cache_put(&uvm_amap_cache, amap);
           UVMHIST_LOG(maphist,"<- done, freed amap = %#jx", (uintptr_t)amap,
               0, 0, 0);
   }
   
   /*
    * amap_extend: extend the size of an amap (if needed)
    *
    * => called from uvm_map when we want to extend an amap to cover
    *    a new mapping (rather than allocate a new one)
    * => amap should be unlocked (we will lock it)
    * => to safely extend an amap it should have a reference count of
    *    one (thus it can't be shared)
    */
   int
   amap_extend(struct vm_map_entry *entry, vsize_t addsize, int flags)
   {
           struct vm_amap *amap = entry->aref.ar_amap;
           int slotoff = entry->aref.ar_pageoff;
           int slotmapped, slotadd, slotneed, slotadded, slotalloc;
           int slotadj, slotarea, slotendoff;
           int oldnslots;
   #ifdef UVM_AMAP_PPREF
           int *newppref, *oldppref;
   #endif
           int i, *newsl, *newbck, *oldsl, *oldbck;
           struct vm_anon **newover, **oldover;
           const km_flag_t kmflags =
               (flags & AMAP_EXTEND_NOWAIT) ? KM_NOSLEEP : KM_SLEEP;
   
           UVMHIST_FUNC(__func__);
           UVMHIST_CALLARGS(maphist, "  (entry=%#jx, addsize=%#jx, flags=%#jx)",
               (uintptr_t)entry, addsize, flags, 0);
   
           /*
            * first, determine how many slots we need in the amap.  don't
            * forget that ar_pageoff could be non-zero: this means that
            * there are some unused slots before us in the amap.
            */
   
           amap_lock(amap, RW_WRITER);
           KASSERT(amap_refs(amap) == 1); /* amap can't be shared */
           AMAP_B2SLOT(slotmapped, entry->end - entry->start); /* slots mapped */
           AMAP_B2SLOT(slotadd, addsize);                  /* slots to add */
           if (flags & AMAP_EXTEND_FORWARDS) {
                   slotneed = slotoff + slotmapped + slotadd;
                   slotadj = 0;
                   slotarea = 0;
           } else {
                   slotneed = slotadd + slotmapped;
                   slotadj = slotadd - slotoff;
                   slotarea = amap->am_maxslot - slotmapped;
           }
   
           /*
            * Because this amap only has 1 ref, we know that there is
            * only one vm_map_entry pointing to it, and the one entry is
            * using slots between slotoff and slotoff + slotmapped.  If
            * we have been using ppref then we know that only slots in
            * the one map entry's range can have anons, since ppref
            * allowed us to free any anons outside that range as other map
            * entries which used this amap were removed. But without ppref,
            * we couldn't know which slots were still needed by other map
            * entries, so we couldn't free any anons as we removed map
            * entries, and so any slot from 0 to am_nslot can have an
            * anon.  But now that we know there is only one map entry
            * left and we know its range, we can free up any anons
            * outside that range.  This is necessary because the rest of
            * this function assumes that there are no anons in the amap
            * outside of the one map entry's range.
            */
   
           slotendoff = slotoff + slotmapped;
           if (amap->am_ppref == PPREF_NONE) {
                   amap_wiperange(amap, 0, slotoff);
                   amap_wiperange(amap, slotendoff, amap->am_nslot - slotendoff);
           }
           for (i = 0; i < slotoff; i++) {
                   KASSERT(amap->am_anon[i] == NULL);
           }
           for (i = slotendoff; i < amap->am_nslot - slotendoff; i++) {
                   KASSERT(amap->am_anon[i] == NULL);
           }
   
           /*
            * case 1: we already have enough slots in the map and thus
            * only need to bump the reference counts on the slots we are
            * adding.
            */
   
           if (flags & AMAP_EXTEND_FORWARDS) {
                   if (amap->am_nslot >= slotneed) {
   #ifdef UVM_AMAP_PPREF
                           if (amap->am_ppref && amap->am_ppref != PPREF_NONE) {
                                   amap_pp_adjref(amap, slotoff + slotmapped,
                                       slotadd, 1);
                           }
   #endif
                           amap_unlock(amap);
                           UVMHIST_LOG(maphist,
                               "<- done (case 1f), amap = %#jx, sltneed=%jd",
                               (uintptr_t)amap, slotneed, 0, 0);
                           return 0;
                   }
           } else {
                   if (slotadj <= 0) {
                           slotoff -= slotadd;
                           entry->aref.ar_pageoff = slotoff;
   #ifdef UVM_AMAP_PPREF
                           if (amap->am_ppref && amap->am_ppref != PPREF_NONE) {
                                   amap_pp_adjref(amap, slotoff, slotadd, 1);
                           }
   #endif
                           amap_unlock(amap);
                           UVMHIST_LOG(maphist,
                               "<- done (case 1b), amap = %#jx, sltneed=%jd",
                               (uintptr_t)amap, slotneed, 0, 0);
                           return 0;
                   }
           }
   
           /*
            * case 2: we pre-allocated slots for use and we just need to
            * bump nslot up to take account for these slots.
            */
   
           if (amap->am_maxslot >= slotneed) {
                   if (flags & AMAP_EXTEND_FORWARDS) {
   #ifdef UVM_AMAP_PPREF
                           if (amap->am_ppref && amap->am_ppref != PPREF_NONE) {
                                   if ((slotoff + slotmapped) < amap->am_nslot)
                                           amap_pp_adjref(amap,
                                               slotoff + slotmapped,
                                               (amap->am_nslot -
                                               (slotoff + slotmapped)), 1);
                                   pp_setreflen(amap->am_ppref, amap->am_nslot, 1,
                                       slotneed - amap->am_nslot);
                           }
   #endif
                           amap->am_nslot = slotneed;
                           amap_unlock(amap);
   
                           /*
                            * no need to zero am_anon since that was done at
                            * alloc time and we never shrink an allocation.
                            */
   
                           UVMHIST_LOG(maphist,"<- done (case 2f), amap = %#jx, "
                               "slotneed=%jd", (uintptr_t)amap, slotneed, 0, 0);
                           return 0;
                   } else {
   #ifdef UVM_AMAP_PPREF
                           if (amap->am_ppref && amap->am_ppref != PPREF_NONE) {
                                   /*
                                    * Slide up the ref counts on the pages that
                                    * are actually in use.
                                    */
                                   memmove(amap->am_ppref + slotarea,
                                       amap->am_ppref + slotoff,
                                       slotmapped * sizeof(int));
                                   /*
                                    * Mark the (adjusted) gap at the front as
                                    * referenced/not referenced.
                                    */
                                   pp_setreflen(amap->am_ppref,
                                       0, 0, slotarea - slotadd);
                                   pp_setreflen(amap->am_ppref,
                                       slotarea - slotadd, 1, slotadd);
                           }
   #endif
   
                           /*
                            * Slide the anon pointers up and clear out
                            * the space we just made.
                            */
                           memmove(amap->am_anon + slotarea,
                               amap->am_anon + slotoff,
                               slotmapped * sizeof(struct vm_anon*));
                           memset(amap->am_anon + slotoff, 0,
                               (slotarea - slotoff) * sizeof(struct vm_anon *));
   
                           /*
                            * Slide the backpointers up, but don't bother
                            * wiping out the old slots.
                            */
                           memmove(amap->am_bckptr + slotarea,
                               amap->am_bckptr + slotoff,
                               slotmapped * sizeof(int));
   
                           /*
                            * Adjust all the useful active slot numbers.
                            */
                           for (i = 0; i < amap->am_nused; i++)
                                   amap->am_slots[i] += (slotarea - slotoff);
   
                           /*
                            * We just filled all the empty space in the
                            * front of the amap by activating a few new
                            * slots.
                            */
                           amap->am_nslot = amap->am_maxslot;
                           entry->aref.ar_pageoff = slotarea - slotadd;
                           amap_unlock(amap);
   
                           UVMHIST_LOG(maphist,"<- done (case 2b), amap = %#jx, "
                               "slotneed=%jd", (uintptr_t)amap, slotneed, 0, 0);
                           return 0;
                   }
           }
   
           /*
            * Case 3: we need to allocate a new amap and copy all the amap
            * data over from old amap to the new one.  Drop the lock before
            * performing allocation.
            *
            * Note: since allocations are likely big, we expect to reduce the
            * memory fragmentation by allocating them in separate blocks.
            */
   
           amap_unlock(amap);
   
           if (slotneed >= UVM_AMAP_LARGE) {
                   return E2BIG;
           }
   
           slotalloc = amap_roundup_slots(slotneed);
   #ifdef UVM_AMAP_PPREF
           newppref = NULL;
           if (amap->am_ppref && amap->am_ppref != PPREF_NONE) {
                   /* Will be handled later if fails. */
                   newppref = kmem_alloc(slotalloc * sizeof(*newppref), kmflags);
           }
   #endif
           newsl = kmem_alloc(slotalloc * sizeof(*newsl), kmflags);
           newbck = kmem_alloc(slotalloc * sizeof(*newbck), kmflags);
           newover = kmem_alloc(slotalloc * sizeof(*newover), kmflags);
           if (newsl == NULL || newbck == NULL || newover == NULL) {
   #ifdef UVM_AMAP_PPREF
                   if (newppref != NULL) {
                           kmem_free(newppref, slotalloc * sizeof(*newppref));
                   }
   #endif
                   if (newsl != NULL) {
                           kmem_free(newsl, slotalloc * sizeof(*newsl));
                   }
                   if (newbck != NULL) {
                           kmem_free(newbck, slotalloc * sizeof(*newbck));
                   }
                   if (newover != NULL) {
                           kmem_free(newover, slotalloc * sizeof(*newover));
                   }
                   return ENOMEM;
           }
           amap_lock(amap, RW_WRITER);
           KASSERT(amap->am_maxslot < slotneed);
   
           /*
            * Copy everything over to new allocated areas.
            */
   
           slotadded = slotalloc - amap->am_nslot;
           if (!(flags & AMAP_EXTEND_FORWARDS))
                   slotarea = slotalloc - slotmapped;
   
           /* do am_slots */
           oldsl = amap->am_slots;
           if (flags & AMAP_EXTEND_FORWARDS)
                   memcpy(newsl, oldsl, sizeof(int) * amap->am_nused);
           else
                   for (i = 0; i < amap->am_nused; i++)
                           newsl[i] = oldsl[i] + slotarea - slotoff;
           amap->am_slots = newsl;
   
           /* do am_anon */
           oldover = amap->am_anon;
           if (flags & AMAP_EXTEND_FORWARDS) {
                   memcpy(newover, oldover,
                       sizeof(struct vm_anon *) * amap->am_nslot);
                   memset(newover + amap->am_nslot, 0,
                       sizeof(struct vm_anon *) * slotadded);
           } else {
                   memcpy(newover + slotarea, oldover + slotoff,
                       sizeof(struct vm_anon *) * slotmapped);
                   memset(newover, 0,
                       sizeof(struct vm_anon *) * slotarea);
           }
           amap->am_anon = newover;
   
           /* do am_bckptr */
           oldbck = amap->am_bckptr;
           if (flags & AMAP_EXTEND_FORWARDS)
                   memcpy(newbck, oldbck, sizeof(int) * amap->am_nslot);
           else
                   memcpy(newbck + slotarea, oldbck + slotoff,
                       sizeof(int) * slotmapped);
           amap->am_bckptr = newbck;
   
   #ifdef UVM_AMAP_PPREF
           /* do ppref */
           oldppref = amap->am_ppref;
           if (newppref) {
                   if (flags & AMAP_EXTEND_FORWARDS) {
                           memcpy(newppref, oldppref,
                               sizeof(int) * amap->am_nslot);
                           memset(newppref + amap->am_nslot, 0,
                               sizeof(int) * slotadded);
                   } else {
                           memcpy(newppref + slotarea, oldppref + slotoff,
                               sizeof(int) * slotmapped);
                   }
                   amap->am_ppref = newppref;
                   if ((flags & AMAP_EXTEND_FORWARDS) &&
                       (slotoff + slotmapped) < amap->am_nslot)
                           amap_pp_adjref(amap, slotoff + slotmapped,
                               (amap->am_nslot - (slotoff + slotmapped)), 1);
                   if (flags & AMAP_EXTEND_FORWARDS)
                           pp_setreflen(newppref, amap->am_nslot, 1,
                               slotneed - amap->am_nslot);
                   else {
                           pp_setreflen(newppref, 0, 0,
                               slotalloc - slotneed);
                           pp_setreflen(newppref, slotalloc - slotneed, 1,
                               slotneed - slotmapped);
                   }
           } else {
                   if (amap->am_ppref)
                           amap->am_ppref = PPREF_NONE;
           }
   #endif
   
           /* update master values */
           if (flags & AMAP_EXTEND_FORWARDS)
                   amap->am_nslot = slotneed;
           else {
                   entry->aref.ar_pageoff = slotarea - slotadd;
                   amap->am_nslot = slotalloc;
           }
           oldnslots = amap->am_maxslot;
           amap->am_maxslot = slotalloc;
           amap_unlock(amap);
   
           kmem_free(oldsl, oldnslots * sizeof(*oldsl));
           kmem_free(oldbck, oldnslots * sizeof(*oldbck));
           kmem_free(oldover, oldnslots * sizeof(*oldover));
   #ifdef UVM_AMAP_PPREF
           if (oldppref && oldppref != PPREF_NONE)
                   kmem_free(oldppref, oldnslots * sizeof(*oldppref));
   #endif
           UVMHIST_LOG(maphist,"<- done (case 3), amap = %#jx, slotneed=%jd",
               (uintptr_t)amap, slotneed, 0, 0);
           return 0;
   }
   
   /*
    * amap_share_protect: change protection of anons in a shared amap
    *
    * for shared amaps, given the current data structure layout, it is
    * not possible for us to directly locate all maps referencing the
    * shared anon (to change the protection).  in order to protect data
    * in shared maps we use pmap_page_protect().  [this is useful for IPC
    * mechanisms like map entry passing that may want to write-protect
    * all mappings of a shared amap.]  we traverse am_anon or am_slots
    * depending on the current state of the amap.
    *
    * => entry's map and amap must be locked by the caller
    */
   void
   amap_share_protect(struct vm_map_entry *entry, vm_prot_t prot)
   {
           struct vm_amap *amap = entry->aref.ar_amap;
           u_int slots, lcv, slot, stop;
           struct vm_anon *anon;
   
           KASSERT(rw_write_held(amap->am_lock));
   
           AMAP_B2SLOT(slots, (entry->end - entry->start));
           stop = entry->aref.ar_pageoff + slots;
   
           if (slots < amap->am_nused) {
                   /*
                    * Cheaper to traverse am_anon.
                    */
                   for (lcv = entry->aref.ar_pageoff ; lcv < stop ; lcv++) {
                           anon = amap->am_anon[lcv];
                           if (anon == NULL) {
                                   continue;
                           }
                           if (anon->an_page) {
                                   pmap_page_protect(anon->an_page, prot);
                           }
                   }
                   return;
           }
   
           /*
            * Cheaper to traverse am_slots.
            */
           for (lcv = 0 ; lcv < amap->am_nused ; lcv++) {
                   slot = amap->am_slots[lcv];
                   if (slot < entry->aref.ar_pageoff || slot >= stop) {
                           continue;
                   }
                   anon = amap->am_anon[slot];
                   if (anon->an_page) {
                           pmap_page_protect(anon->an_page, prot);
                   }
           }
   }
   
   /*
    * amap_wipeout: wipeout all anon's in an amap; then free the amap!
    *
    * => Called from amap_unref(), when reference count drops to zero.
    * => amap must be locked.
    */
   
   void
   amap_wipeout(struct vm_amap *amap)
   {
           u_int lcv;
   
           UVMHIST_FUNC(__func__);
           UVMHIST_CALLARGS(maphist,"(amap=%#jx)", (uintptr_t)amap, 0,0,0);
   
           KASSERT(rw_write_held(amap->am_lock));
           KASSERT(amap->am_ref == 0);
   
           if (__predict_false(amap->am_flags & AMAP_SWAPOFF)) {
                   /*
                    * Note: amap_swap_off() will call us again.
                    */
                   amap_unlock(amap);
                   return;
           }
   
           for (lcv = 0 ; lcv < amap->am_nused ; lcv++) {
                   struct vm_anon *anon;
                   u_int slot;
   
                   slot = amap->am_slots[lcv];
                   anon = amap->am_anon[slot];
                   KASSERT(anon != NULL && anon->an_ref != 0);
   
                   KASSERT(anon->an_lock == amap->am_lock);
                   UVMHIST_LOG(maphist,"  processing anon %#jx, ref=%jd",
                       (uintptr_t)anon, anon->an_ref, 0, 0);
   
                   /*
                    * Drop the reference.
                    */
   
                   if (__predict_true(--anon->an_ref == 0)) {
                           uvm_anfree(anon);
                   }
                   if (__predict_false((lcv & 31) == 31)) {
                           preempt_point();
                   }
           }
   
           /*
            * Finally, destroy the amap.
            */
   
           amap->am_nused = 0;
           amap_unlock(amap);
           amap_free(amap);
           UVMHIST_LOG(maphist,"<- done!", 0,0,0,0);
   }
   
   /*
    * amap_copy: ensure that a map entry's "needs_copy" flag is false
    *      by copying the amap if necessary.
    *
    * => an entry with a null amap pointer will get a new (blank) one.
    * => the map that the map entry belongs to must be locked by caller.
    * => the amap currently attached to "entry" (if any) must be unlocked.
    * => if canchunk is true, then we may clip the entry into a chunk
    * => "startva" and "endva" are used only if canchunk is true.  they are
    *     used to limit chunking (e.g. if you have a large space that you
    *     know you are going to need to allocate amaps for, there is no point
    *     in allowing that to be chunked)
    */
   
   void
   amap_copy(struct vm_map *map, struct vm_map_entry *entry, int flags,
       vaddr_t startva, vaddr_t endva)
   {
           const int waitf = (flags & AMAP_COPY_NOWAIT) ? UVM_FLAG_NOWAIT : 0;
           struct vm_amap *amap, *srcamap;
           u_int slots, lcv;
           krwlock_t *oldlock;
           vsize_t len;
   
           UVMHIST_FUNC(__func__);
           UVMHIST_CALLARGS(maphist, "  (map=%#jx, entry=%#jx, flags=%#jx)",
               (uintptr_t)map, (uintptr_t)entry, flags, -2);
   
           KASSERT(map != kernel_map);     /* we use nointr pool */
   
           srcamap = entry->aref.ar_amap;
           len = entry->end - entry->start;
   
           /*
            * Is there an amap to copy?  If not, create one.
            */
   
           if (srcamap == NULL) {
                   const bool canchunk = (flags & AMAP_COPY_NOCHUNK) == 0;
   
                   /*
                    * Check to see if we have a large amap that we can
                    * chunk.  We align startva/endva to chunk-sized
                    * boundaries and then clip to them.
                    */
   
                   if (canchunk && atop(len) >= UVM_AMAP_LARGE) {
                           vsize_t chunksize;
   
                           /* Convert slots to bytes. */
                           chunksize = UVM_AMAP_CHUNK << PAGE_SHIFT;
                           startva = (startva / chunksize) * chunksize;
                           endva = roundup(endva, chunksize);
                           UVMHIST_LOG(maphist,
                               "  chunk amap ==> clip %#jx->%#jx to %#jx->%#jx",
                               entry->start, entry->end, startva, endva);
                           UVM_MAP_CLIP_START(map, entry, startva);
   
                           /* Watch out for endva wrap-around! */
                           if (endva >= startva) {
                                   UVM_MAP_CLIP_END(map, entry, endva);
                           }
                   }
   
                   if ((flags & AMAP_COPY_NOMERGE) == 0 &&
                       uvm_mapent_trymerge(map, entry, UVM_MERGE_COPYING)) {
                           return;
                   }
   
                   UVMHIST_LOG(maphist, "<- done [creating new amap %#jx->%#jx]",
                       entry->start, entry->end, 0, 0);
   
                   /*
                    * Allocate an initialised amap and install it.
                    * Note: we must update the length after clipping.
                    */
                   len = entry->end - entry->start;
                   entry->aref.ar_pageoff = 0;
                   entry->aref.ar_amap = amap_alloc(len, 0, waitf);
                   if (entry->aref.ar_amap != NULL) {
                           entry->etype &= ~UVM_ET_NEEDSCOPY;
                   }
                   return;
           }
   
           /*
            * First check and see if we are the only map entry referencing
            * he amap we currently have.  If so, then just take it over instead
            * of copying it.  Note that we are reading am_ref without lock held
            * as the value value can only be one if we have the only reference
            * to the amap (via our locked map).  If the value is greater than
            * one, then allocate amap and re-check the value.
            */
   
           if (srcamap->am_ref == 1) {
                   entry->etype &= ~UVM_ET_NEEDSCOPY;
                   UVMHIST_LOG(maphist, "<- done [ref cnt = 1, took it over]",
                       0, 0, 0, 0);
                   return;
           }
   
           UVMHIST_LOG(maphist,"  amap=%#jx, ref=%jd, must copy it",
               (uintptr_t)srcamap, srcamap->am_ref, 0, 0);
   
           /*
            * Allocate a new amap (note: not initialised, etc).
            */
   
           AMAP_B2SLOT(slots, len);
           amap = amap_alloc1(slots, 0, waitf);
           if (amap == NULL) {
                   UVMHIST_LOG(maphist, "  amap_alloc1 failed", 0,0,0,0);
                   return;
           }
   
           /*
            * Make the new amap share the source amap's lock, and then lock
            * both.  We must do this before we set am_nused != 0, otherwise
            * amap_swap_off() can become interested in the amap.
            */
   
           oldlock = amap->am_lock;
           mutex_enter(&amap_list_lock);
           amap->am_lock = srcamap->am_lock;
           mutex_exit(&amap_list_lock);
           rw_obj_hold(amap->am_lock);
           rw_obj_free(oldlock);
   
           amap_lock(srcamap, RW_WRITER);
   
           /*
            * Re-check the reference count with the lock held.  If it has
            * dropped to one - we can take over the existing map.
            */
   
           if (srcamap->am_ref == 1) {
                   /* Just take over the existing amap. */
                   entry->etype &= ~UVM_ET_NEEDSCOPY;
                   amap_unlock(srcamap);
                   /* Destroy the new (unused) amap. */
                   amap->am_ref--;
                   amap_free(amap);
                   return;
           }
   
           /*
            * Copy the slots.  Zero the padded part.
            */
   
           UVMHIST_LOG(maphist, "  copying amap now",0, 0, 0, 0);
           for (lcv = 0 ; lcv < slots; lcv++) {
                   amap->am_anon[lcv] =
                       srcamap->am_anon[entry->aref.ar_pageoff + lcv];
                   if (amap->am_anon[lcv] == NULL)
                           continue;
                   KASSERT(amap->am_anon[lcv]->an_lock == srcamap->am_lock);
                   KASSERT(amap->am_anon[lcv]->an_ref > 0);
                   KASSERT(amap->am_nused < amap->am_maxslot);
                   amap->am_anon[lcv]->an_ref++;
                   amap->am_bckptr[lcv] = amap->am_nused;
                   amap->am_slots[amap->am_nused] = lcv;
                   amap->am_nused++;
           }
           memset(&amap->am_anon[lcv], 0,
               (amap->am_maxslot - lcv) * sizeof(struct vm_anon *));
   
           /*
            * Drop our reference to the old amap (srcamap) and unlock.
            * Since the reference count on srcamap is greater than one,
            * (we checked above), it cannot drop to zero while it is locked.
            */
   
           srcamap->am_ref--;
           KASSERT(srcamap->am_ref > 0);
   
           if (srcamap->am_ref == 1 && (srcamap->am_flags & AMAP_SHARED) != 0) {
                   srcamap->am_flags &= ~AMAP_SHARED;
           }
   #ifdef UVM_AMAP_PPREF
           if (srcamap->am_ppref && srcamap->am_ppref != PPREF_NONE) {
                   amap_pp_adjref(srcamap, entry->aref.ar_pageoff,
                       len >> PAGE_SHIFT, -1);
           }
   #endif
   
           amap_unlock(srcamap);
   
           /*
            * Install new amap.
            */
   
           entry->aref.ar_pageoff = 0;
           entry->aref.ar_amap = amap;
           entry->etype &= ~UVM_ET_NEEDSCOPY;
           UVMHIST_LOG(maphist, "<- done",0, 0, 0, 0);
  }
  
  /*
   * amap_cow_now: resolve all copy-on-write faults in an amap now for fork(2)
   *
   *      called during fork(2) when the parent process has a wired map
   *      entry.   in that case we want to avoid write-protecting pages
   *      in the parent's map (e.g. like what you'd do for a COW page)
   *      so we resolve the COW here.
   *
   * => assume parent's entry was wired, thus all pages are resident.
   * => assume pages that are loaned out (loan_count) are already mapped
   *      read-only in all maps, and thus no need for us to worry about them
   * => assume both parent and child vm_map's are locked
   * => caller passes child's map/entry in to us
   * => if we run out of memory we will unlock the amap and sleep _with_ the
   *      parent and child vm_map's locked(!).    we have to do this since
   *      we are in the middle of a fork(2) and we can't let the parent
   *      map change until we are done copying all the map entrys.
   * => XXXCDC: out of memory should cause fork to fail, but there is
   *      currently no easy way to do this (needs fix)
   */
  
  void
  amap_cow_now(struct vm_map *map, struct vm_map_entry *entry)
  {
          struct vm_amap *amap = entry->aref.ar_amap;
          struct vm_anon *anon, *nanon;
          struct vm_page *pg, *npg;
          u_int lcv, slot;
  
          /*
           * note that if we unlock the amap then we must ReStart the "lcv" for
           * loop because some other process could reorder the anon's in the
           * am_anon[] array on us while the lock is dropped.
           */
  
  ReStart:
          amap_lock(amap, RW_WRITER);
          for (lcv = 0 ; lcv < amap->am_nused ; lcv++) {
                  slot = amap->am_slots[lcv];
                  anon = amap->am_anon[slot];
                  KASSERT(anon->an_lock == amap->am_lock);
  
                  /*
                   * If anon has only one reference - we must have already
                   * copied it.  This can happen if we needed to sleep waiting
                   * for memory in a previous run through this loop.  The new
                   * page might even have been paged out, since is not wired.
                   */
  
                  if (anon->an_ref == 1) {
                          KASSERT(anon->an_page != NULL || anon->an_swslot != 0);
                          continue;
                  }
  
                  /*
                   * The old page must be resident since the parent is wired.
                   */
  
                  pg = anon->an_page;
                  KASSERT(pg != NULL);
                  KASSERT(pg->wire_count > 0);
  
                  /*
                   * If the page is loaned then it must already be mapped
                   * read-only and we don't need to copy it.
                   */
  
                  if (pg->loan_count != 0) {
                          continue;
                  }
                  KASSERT(pg->uanon == anon && pg->uobject == NULL);
  
                  /*
                   * If the page is busy, then we have to unlock, wait for
                   * it and then restart.
                   */
  
                  if (pg->flags & PG_BUSY) {
                          uvm_pagewait(pg, amap->am_lock, "cownow");
                          goto ReStart;
                  }
  
                  /*
                   * Perform a copy-on-write.
                   * First - get a new anon and a page.
                   */
  
                  nanon = uvm_analloc();
                  if (nanon) {
                          nanon->an_lock = amap->am_lock;
                          npg = uvm_pagealloc(NULL, 0, nanon, 0);
                  } else {
                          npg = NULL;
                  }
                  if (nanon == NULL || npg == NULL) {
                          amap_unlock(amap);
                          if (nanon) {
                                  nanon->an_lock = NULL;
                                  nanon->an_ref--;
                                  KASSERT(nanon->an_ref == 0);
                                  uvm_anfree(nanon);
                          }
                          uvm_wait("cownowpage");
                          goto ReStart;
                  }
  
                  /*
                   * Copy the data and replace anon with the new one.
                   * Also, setup its lock (share the with amap's lock).
                   */
  
                  uvm_pagecopy(pg, npg);
                  anon->an_ref--;
                  KASSERT(anon->an_ref > 0);
                  amap->am_anon[slot] = nanon;
  
                  /*
                   * Drop PG_BUSY on new page.  Since its owner was write
                   * locked all this time - it cannot be PG_RELEASED or
                   * waited on.
                   */
                  uvm_pagelock(npg);
                  uvm_pageactivate(npg);
                  uvm_pageunlock(npg);
                  npg->flags &= ~(PG_BUSY|PG_FAKE);
                  UVM_PAGE_OWN(npg, NULL);
          }
          amap_unlock(amap);
  }
  
  /*
   * amap_splitref: split a single reference into two separate references
   *
   * => called from uvm_map's clip routines
   * => origref's map should be locked
   * => origref->ar_amap should be unlocked (we will lock)
   */
  void
  amap_splitref(struct vm_aref *origref, struct vm_aref *splitref, vaddr_t offset)
  {
          struct vm_amap *amap = origref->ar_amap;
          u_int leftslots;
  
          KASSERT(splitref->ar_amap == origref->ar_amap);
          AMAP_B2SLOT(leftslots, offset);
          KASSERT(leftslots != 0);
  
          amap_lock(amap, RW_WRITER);
          KASSERT(amap->am_nslot - origref->ar_pageoff - leftslots > 0);
  
  #ifdef UVM_AMAP_PPREF
          /* Establish ppref before we add a duplicate reference to the amap. */
          if (amap->am_ppref == NULL) {
                  amap_pp_establish(amap, origref->ar_pageoff);
          }
  #endif
          /* Note: not a share reference. */
          amap->am_ref++;
          splitref->ar_pageoff = origref->ar_pageoff + leftslots;
          amap_unlock(amap);
  }
  
  #ifdef UVM_AMAP_PPREF
  
  /*
   * amap_pp_establish: add a ppref array to an amap, if possible.
   *
   * => amap should be locked by caller.
   */
  void
  amap_pp_establish(struct vm_amap *amap, vaddr_t offset)
  {
          const size_t sz = amap->am_maxslot * sizeof(*amap->am_ppref);
  
          KASSERT(rw_write_held(amap->am_lock));
  
          amap->am_ppref = kmem_zalloc(sz, KM_NOSLEEP);
          if (amap->am_ppref == NULL) {
                  /* Failure - just do not use ppref. */
                  amap->am_ppref = PPREF_NONE;
                  return;
          }
          pp_setreflen(amap->am_ppref, 0, 0, offset);
          pp_setreflen(amap->am_ppref, offset, amap->am_ref,
              amap->am_nslot - offset);
  }
  
  /*
   * amap_pp_adjref: adjust reference count to a part of an amap using the
   * per-page reference count array.
   *
   * => caller must check that ppref != PPREF_NONE before calling.
   * => map and amap must be locked.
   */
  void
  amap_pp_adjref(struct vm_amap *amap, int curslot, vsize_t slotlen, int adjval)
  {
          int stopslot, *ppref, lcv, prevlcv;
          int ref, len, prevref, prevlen;
  
          KASSERT(rw_write_held(amap->am_lock));
  
          stopslot = curslot + slotlen;
          ppref = amap->am_ppref;
          prevlcv = 0;
  
          /*
           * Advance to the correct place in the array, fragment if needed.
           */
  
          for (lcv = 0 ; lcv < curslot ; lcv += len) {
                  pp_getreflen(ppref, lcv, &ref, &len);
                  if (lcv + len > curslot) {     /* goes past start? */
                          pp_setreflen(ppref, lcv, ref, curslot - lcv);
                          pp_setreflen(ppref, curslot, ref, len - (curslot -lcv));
                          len = curslot - lcv;   /* new length of entry @ lcv */
                  }
                  prevlcv = lcv;
          }
          if (lcv == 0) {
                  /*
                   * Ensure that the "prevref == ref" test below always
                   * fails, since we are starting from the beginning of
                   * the ppref array; that is, there is no previous chunk.
                   */
                  prevref = -1;
                  prevlen = 0;
          } else {
                  pp_getreflen(ppref, prevlcv, &prevref, &prevlen);
          }
  
          /*
           * Now adjust reference counts in range.  Merge the first
           * changed entry with the last unchanged entry if possible.
           */
          KASSERT(lcv == curslot);
          for (/* lcv already set */; lcv < stopslot ; lcv += len) {
                  pp_getreflen(ppref, lcv, &ref, &len);
                  if (lcv + len > stopslot) {     /* goes past end? */
                          pp_setreflen(ppref, lcv, ref, stopslot - lcv);
                          pp_setreflen(ppref, stopslot, ref,
                              len - (stopslot - lcv));
                          len = stopslot - lcv;
                  }
                  ref += adjval;
                  KASSERT(ref >= 0);
                  KASSERT(ref <= amap->am_ref);
                  if (lcv == prevlcv + prevlen && ref == prevref) {
                          pp_setreflen(ppref, prevlcv, ref, prevlen + len);
                  } else {
                          pp_setreflen(ppref, lcv, ref, len);
                  }
                  if (ref == 0) {
                          amap_wiperange(amap, lcv, len);
                  }
          }
  }
  
  /*
   * amap_wiperange: wipe out a range of an amap.
   * Note: different from amap_wipeout because the amap is kept intact.
   *
   * => Both map and amap must be locked by caller.
   */
  void
  amap_wiperange(struct vm_amap *amap, int slotoff, int slots)
  {
          u_int lcv, stop, slotend;
          bool byanon;
  
          KASSERT(rw_write_held(amap->am_lock));
  
          /*
           * We can either traverse the amap by am_anon or by am_slots.
           * Determine which way is less expensive.
           */
  
          if (slots < amap->am_nused) {
                  byanon = true;
                  lcv = slotoff;
                  stop = slotoff + slots;
                  slotend = 0;
          } else {
                  byanon = false;
                  lcv = 0;
                  stop = amap->am_nused;
                  slotend = slotoff + slots;
          }
  
          while (lcv < stop) {
                  struct vm_anon *anon;
                  u_int curslot, ptr, last;
  
                  if (byanon) {
                          curslot = lcv++;        /* lcv advances here */
                          if (amap->am_anon[curslot] == NULL)
                                  continue;
                  } else {
                          curslot = amap->am_slots[lcv];
                          if (curslot < slotoff || curslot >= slotend) {
                                  lcv++;          /* lcv advances here */
                                  continue;
                          }
                          stop--; /* drop stop, since anon will be removed */
                  }
                  anon = amap->am_anon[curslot];
                  KASSERT(anon->an_lock == amap->am_lock);
  
                  /*
                   * Remove anon from the amap.
                   */
  
                  amap->am_anon[curslot] = NULL;
                  ptr = amap->am_bckptr[curslot];
                  last = amap->am_nused - 1;
                  if (ptr != last) {
                          amap->am_slots[ptr] = amap->am_slots[last];
                          amap->am_bckptr[amap->am_slots[ptr]] = ptr;
                  }
                  amap->am_nused--;
  
                  /*
                   * Drop its reference count.
                   */
  
                  KASSERT(anon->an_lock == amap->am_lock);
                  if (--anon->an_ref == 0) {
                          uvm_anfree(anon);
                  }
          }
  }
  
  #endif
  
  #if defined(VMSWAP)
  
  /*
   * amap_swap_off: pagein anonymous pages in amaps and drop swap slots.
   *
   * => called with swap_syscall_lock held.
   * => note that we don't always traverse all anons.
   *    eg. amaps being wiped out, released anons.
   * => return true if failed.
   */
  
  bool
  amap_swap_off(int startslot, int endslot)
  {
          struct vm_amap *am;
          struct vm_amap *am_next;
          struct vm_amap marker_prev;
          struct vm_amap marker_next;
          bool rv = false;
  
  #if defined(DIAGNOSTIC)
          memset(&marker_prev, 0, sizeof(marker_prev));
          memset(&marker_next, 0, sizeof(marker_next));
  #endif /* defined(DIAGNOSTIC) */
  
          mutex_enter(&amap_list_lock);
          for (am = LIST_FIRST(&amap_list); am != NULL && !rv; am = am_next) {
                  int i;
  
                  LIST_INSERT_BEFORE(am, &marker_prev, am_list);
                  LIST_INSERT_AFTER(am, &marker_next, am_list);
  
                  /* amap_list_lock prevents the lock pointer from changing. */
                  if (!amap_lock_try(am, RW_WRITER)) {
                          (void)kpause("amapswpo", false, 1, &amap_list_lock);
                          am_next = LIST_NEXT(&marker_prev, am_list);
                          if (am_next == &marker_next) {
                                  am_next = LIST_NEXT(am_next, am_list);
                          } else {
                                  KASSERT(LIST_NEXT(am_next, am_list) ==
                                      &marker_next);
                          }
                          LIST_REMOVE(&marker_prev, am_list);
                          LIST_REMOVE(&marker_next, am_list);
                          continue;
                  }
  
                  mutex_exit(&amap_list_lock);
  
                  /* If am_nused == 0, the amap could be free - careful. */
                  for (i = 0; i < am->am_nused; i++) {
                          int slot;
                          int swslot;
                          struct vm_anon *anon;
  
                          slot = am->am_slots[i];
                          anon = am->am_anon[slot];
                          KASSERT(anon->an_lock == am->am_lock);
  
                          swslot = anon->an_swslot;
                          if (swslot < startslot || endslot <= swslot) {
                                  continue;
                          }
  
                          am->am_flags |= AMAP_SWAPOFF;
  
                          rv = uvm_anon_pagein(am, anon);
                          amap_lock(am, RW_WRITER);
  
                          am->am_flags &= ~AMAP_SWAPOFF;
                          if (amap_refs(am) == 0) {
                                  amap_wipeout(am);
                                  am = NULL;
                                  break;
                          }
                          if (rv) {
                                  break;
                          }
                          i = 0;
                  }
  
                  if (am) {
                          amap_unlock(am);
                  }
  
                  mutex_enter(&amap_list_lock);
                  KASSERT(LIST_NEXT(&marker_prev, am_list) == &marker_next ||
                      LIST_NEXT(LIST_NEXT(&marker_prev, am_list), am_list) ==
                      &marker_next);
                  am_next = LIST_NEXT(&marker_next, am_list);
                  LIST_REMOVE(&marker_prev, am_list);
                  LIST_REMOVE(&marker_next, am_list);
          }
          mutex_exit(&amap_list_lock);
  
          return rv;
  }
  
  #endif /* defined(VMSWAP) */
  
  /*
   * amap_lookup: look up a page in an amap.
   *
   * => amap should be locked by caller.
   */
  struct vm_anon *
  amap_lookup(struct vm_aref *aref, vaddr_t offset)
  {
          struct vm_amap *amap = aref->ar_amap;
          struct vm_anon *an;
          u_int slot;
  
          UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);
          KASSERT(rw_lock_held(amap->am_lock));
  
          AMAP_B2SLOT(slot, offset);
          slot += aref->ar_pageoff;
          an = amap->am_anon[slot];
  
          UVMHIST_LOG(maphist,
              "<- done (amap=%#jx, offset=%#jx, result=%#jx)",
              (uintptr_t)amap, offset, (uintptr_t)an, 0);
  
          KASSERT(slot < amap->am_nslot);
          KASSERT(an == NULL || an->an_ref != 0);
          KASSERT(an == NULL || an->an_lock == amap->am_lock);
          return an;
  }
  
  /*
   * amap_lookups: look up a range of pages in an amap.
   *
   * => amap should be locked by caller.
   */
  void
  amap_lookups(struct vm_aref *aref, vaddr_t offset, struct vm_anon **anons,
      int npages)
  {
          struct vm_amap *amap = aref->ar_amap;
          u_int slot;
  
          UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);
          KASSERT(rw_lock_held(amap->am_lock));
  
          AMAP_B2SLOT(slot, offset);
          slot += aref->ar_pageoff;
  
          UVMHIST_LOG(maphist, "  slot=%u, npages=%d, nslot=%d",
              slot, npages, amap->am_nslot, 0);
  
          KASSERT((slot + (npages - 1)) < amap->am_nslot);
          memcpy(anons, &amap->am_anon[slot], npages * sizeof(struct vm_anon *));
  
  #if defined(DIAGNOSTIC)
          for (int i = 0; i < npages; i++) {
                  struct vm_anon * const an = anons[i];
                  if (an == NULL) {
                          continue;
                  }
                  KASSERT(an->an_ref != 0);
                  KASSERT(an->an_lock == amap->am_lock);
          }
  #endif
          UVMHIST_LOG(maphist, "<- done", 0, 0, 0, 0);
  }
  
  /*
   * amap_add: add (or replace) a page to an amap.
   *
   * => amap should be locked by caller.
   * => anon must have the lock associated with this amap.
   */
  void
  amap_add(struct vm_aref *aref, vaddr_t offset, struct vm_anon *anon,
      bool replace)
  {
          struct vm_amap *amap = aref->ar_amap;
          u_int slot;
  
          UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);
          KASSERT(rw_write_held(amap->am_lock));
          KASSERT(anon->an_lock == amap->am_lock);
  
          AMAP_B2SLOT(slot, offset);
          slot += aref->ar_pageoff;
          KASSERT(slot < amap->am_nslot);
  
          if (replace) {
                  struct vm_anon *oanon = amap->am_anon[slot];
  
                  KASSERT(oanon != NULL);
                  if (oanon->an_page && (amap->am_flags & AMAP_SHARED) != 0) {
                          pmap_page_protect(oanon->an_page, VM_PROT_NONE);
                          /*
                           * XXX: suppose page is supposed to be wired somewhere?
                           */
                  }
          } else {
                  KASSERT(amap->am_anon[slot] == NULL);
                  KASSERT(amap->am_nused < amap->am_maxslot);
                  amap->am_bckptr[slot] = amap->am_nused;
                  amap->am_slots[amap->am_nused] = slot;
                  amap->am_nused++;
          }
          amap->am_anon[slot] = anon;
          UVMHIST_LOG(maphist,
              "<- done (amap=%#jx, offset=%#x, anon=%#jx, rep=%d)",
              (uintptr_t)amap, offset, (uintptr_t)anon, replace);
  }
  
  /*
   * amap_unadd: remove a page from an amap.
   *
   * => amap should be locked by caller.
   */
  void
  amap_unadd(struct vm_aref *aref, vaddr_t offset)
  {
          struct vm_amap *amap = aref->ar_amap;
          u_int slot, ptr, last;
  
          UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);
          KASSERT(rw_write_held(amap->am_lock));
  
          AMAP_B2SLOT(slot, offset);
          slot += aref->ar_pageoff;
          KASSERT(slot < amap->am_nslot);
          KASSERT(amap->am_anon[slot] != NULL);
          KASSERT(amap->am_anon[slot]->an_lock == amap->am_lock);
  
          amap->am_anon[slot] = NULL;
          ptr = amap->am_bckptr[slot];
  
          last = amap->am_nused - 1;
          if (ptr != last) {
                  /* Move the last entry to keep the slots contiguous. */
                  amap->am_slots[ptr] = amap->am_slots[last];
                  amap->am_bckptr[amap->am_slots[ptr]] = ptr;
          }
          amap->am_nused--;
          UVMHIST_LOG(maphist, "<- done (amap=%#jx, slot=%#jx)",
              (uintptr_t)amap, slot,0, 0);
  }
  
  /*
   * amap_adjref_anons: adjust the reference count(s) on amap and its anons.
   */
  static void
  amap_adjref_anons(struct vm_amap *amap, vaddr_t offset, vsize_t len,
      int refv, bool all)
  {
  
  #ifdef UVM_AMAP_PPREF
          KASSERT(rw_write_held(amap->am_lock));
  
          /*
           * We must establish the ppref array before changing am_ref
           * so that the ppref values match the current amap refcount.
           */
  
          if (amap->am_ppref == NULL) {
                  amap_pp_establish(amap, offset);
          }
  #endif
  
          amap->am_ref += refv;
  
  #ifdef UVM_AMAP_PPREF
          if (amap->am_ppref && amap->am_ppref != PPREF_NONE) {
                  amap_pp_adjref(amap, offset, len, refv);
          }
  #endif
          amap_unlock(amap);
  }
  
  /*
   * amap_ref: gain a reference to an amap.
   *
   * => amap must not be locked (we will lock).
   * => "offset" and "len" are in units of pages.
   * => Called at fork time to gain the child's reference.
   */
  void
  amap_ref(struct vm_amap *amap, vaddr_t offset, vsize_t len, int flags)
  {
          UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);
  
          amap_lock(amap, RW_WRITER);
          if (flags & AMAP_SHARED) {
                  amap->am_flags |= AMAP_SHARED;
          }
          amap_adjref_anons(amap, offset, len, 1, (flags & AMAP_REFALL) != 0);
  
          UVMHIST_LOG(maphist,"<- done!  amap=%#jx", (uintptr_t)amap, 0, 0, 0);
  }
  
  /*
   * amap_unref: remove a reference to an amap.
   *
   * => All pmap-level references to this amap must be already removed.
   * => Called from uvm_unmap_detach(); entry is already removed from the map.
   * => We will lock amap, so it must be unlocked.
   */
  void
  amap_unref(struct vm_amap *amap, vaddr_t offset, vsize_t len, bool all)
  {
          UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);
  
          amap_lock(amap, RW_WRITER);
  
          UVMHIST_LOG(maphist,"  amap=%#jx  refs=%d, nused=%d",
              (uintptr_t)amap, amap->am_ref, amap->am_nused, 0);
          KASSERT(amap->am_ref > 0);
  
          if (amap->am_ref == 1) {
  
                  /*
                   * If the last reference - wipeout and destroy the amap.
                   */
                  amap->am_ref--;
                  amap_wipeout(amap);
                  UVMHIST_LOG(maphist,"<- done (was last ref)!", 0, 0, 0, 0);
                  return;
          }
  
          /*
           * Otherwise, drop the reference count(s) on anons.
           */
  
          if (amap->am_ref == 2 && (amap->am_flags & AMAP_SHARED) != 0) {
                  amap->am_flags &= ~AMAP_SHARED;
          }
          amap_adjref_anons(amap, offset, len, -1, all);
  
          UVMHIST_LOG(maphist,"<- done!", 0, 0, 0, 0);
  }

Cache object: 68c1c17249501e23fc8e719326302684