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[netbsd-mini2440.git] / sys / uvm / uvm_amap.c

/*      $NetBSD: uvm_amap.c,v 1.86 2009/03/28 21:45:55 rmind 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by Charles D. Cranor and
 *      Washington University.
 * 4. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * 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 1.86 2009/03/28 21:45:55 rmind Exp $");

#include "opt_uvmhist.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.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;
static LIST_HEAD(, vm_amap) amap_list;

/*
 * local functions
 */

static inline void
amap_list_insert(struct vm_amap *amap)
{

        mutex_enter(&amap_list_lock);
        LIST_INSERT_HEAD(&amap_list, amap, am_list);
        mutex_exit(&amap_list_lock);
}

static inline void
amap_list_remove(struct vm_amap *amap)
{

        mutex_enter(&amap_list_lock);
        LIST_REMOVE(amap, am_list);
        mutex_exit(&amap_list_lock);
}

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 malloc of the array fails
 * (M_NOWAIT), 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: internal function that allocates an amap, but does not
 *      init the overlay.
 *
 * => lock on returned amap is init'd
 */
static inline struct vm_amap *
amap_alloc1(int slots, int padslots, int waitf)
{
        struct vm_amap *amap;
        int totalslots;
        km_flag_t kmflags;

        amap = pool_cache_get(&uvm_amap_cache,
            ((waitf & UVM_FLAG_NOWAIT) != 0) ? PR_NOWAIT : PR_WAITOK);
        if (amap == NULL)
                return(NULL);

        kmflags = ((waitf & UVM_FLAG_NOWAIT) != 0) ? KM_NOSLEEP : KM_SLEEP;
        totalslots = amap_roundup_slots(slots + padslots);
        mutex_init(&amap->am_l, MUTEX_DEFAULT, IPL_NONE);
        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;
        amap->am_nused = 0;

        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:
        mutex_destroy(&amap->am_l);
        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 ((waitf & UVM_FLAG_NOWAIT) != 0) {
                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("amap_alloc"); 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 *));
                amap_list_insert(amap);
        }

        UVMHIST_LOG(maphist,"<- done, amap = 0x%x, sz=%d", amap, sz, 0, 0);
        return(amap);
}

/*
 * 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, 0,
            "amappl", NULL, IPL_NONE, NULL, NULL, 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("amap_free"); UVMHIST_CALLED(maphist);

        KASSERT(amap->am_ref == 0 && amap->am_nused == 0);
        KASSERT((amap->am_flags & AMAP_SWAPOFF) == 0);
        KASSERT(!mutex_owned(&amap->am_l));
        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
        mutex_destroy(&amap->am_l);
        pool_cache_put(&uvm_amap_cache, amap);
        UVMHIST_LOG(maphist,"<- done, freed amap = 0x%x", 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, slotspace;
        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("amap_extend"); UVMHIST_CALLED(maphist);

        UVMHIST_LOG(maphist, "  (entry=0x%x, addsize=0x%x, flags=0x%x)",
            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);
        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;
                slotspace = 0;
        }
        else {
                slotneed = slotadd + slotmapped;
                slotadj = slotadd - slotoff;
                slotspace = amap->am_maxslot - slotmapped;
        }

        /*
         * 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 = 0x%x, sltneed=%d",
                            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 = 0x%x, sltneed=%d",
                            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 = 0x%x, "
                            "slotneed=%d", 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 + slotspace,
                                    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, slotspace - slotadd);
                                pp_setreflen(amap->am_ppref,
                                    slotspace - slotadd, 1, slotadd);
                        }
#endif

                        /*
                         * Slide the anon pointers up and clear out
                         * the space we just made.
                         */
                        memmove(amap->am_anon + slotspace,
                            amap->am_anon + slotoff,
                            slotmapped * sizeof(struct vm_anon*));
                        memset(amap->am_anon + slotoff, 0,
                            (slotspace - slotoff) * sizeof(struct vm_anon *));

                        /*
                         * Slide the backpointers up, but don't bother
                         * wiping out the old slots.
                         */
                        memmove(amap->am_bckptr + slotspace,
                            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] += (slotspace - 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 = slotspace - slotadd;
                        amap_unlock(amap);

                        UVMHIST_LOG(maphist,"<- done (case 2b), amap = 0x%x, "
                            "slotneed=%d", amap, slotneed, 0, 0);
                        return 0;
                }
        }

        /*
         * case 3: we need to malloc a new amap and copy all the amap
         * data over from old amap to the new one.
         *
         * note that the use of a kernel realloc() probably would not
         * help here, since we wish to abort cleanly if one of the
         * three (or four) mallocs fails.
         */

        amap_unlock(amap);      /* unlock in case we sleep in malloc */

        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)
                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);
        KASSERT(amap->am_maxslot < slotneed);

        /*
         * now copy everything over to new malloc'd areas...
         */

        slotadded = slotalloc - amap->am_nslot;
        if (!(flags & AMAP_EXTEND_FORWARDS))
                slotspace = 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] + slotspace - 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 + slotspace, oldover + slotoff,
                    sizeof(struct vm_anon *) * slotmapped);
                memset(newover, 0,
                    sizeof(struct vm_anon *) * slotspace);
        }
        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 + slotspace, 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 + slotspace, 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 = slotspace - 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 = 0x%x, slotneed=%d",
            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;
        int slots, lcv, slot, stop;

        KASSERT(mutex_owned(&amap->am_l));

        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++) {
                        if (amap->am_anon[lcv] == NULL)
                                continue;
                        if (amap->am_anon[lcv]->an_page != NULL)
                                pmap_page_protect(amap->am_anon[lcv]->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;
                if (amap->am_anon[slot]->an_page != NULL)
                        pmap_page_protect(amap->am_anon[slot]->an_page, prot);
        }
}

/*
 * amap_wipeout: wipeout all anon's in an amap; then free the amap!
 *
 * => called from amap_unref when the final reference to an amap is
 *      discarded (i.e. when reference count drops to 0)
 * => the amap should be locked (by the caller)
 */

void
amap_wipeout(struct vm_amap *amap)
{
        int lcv, slot;
        struct vm_anon *anon;
        UVMHIST_FUNC("amap_wipeout"); UVMHIST_CALLED(maphist);
        UVMHIST_LOG(maphist,"(amap=0x%x)", amap, 0,0,0);

        KASSERT(amap->am_ref == 0);

        if (__predict_false((amap->am_flags & AMAP_SWAPOFF) != 0)) {
                /*
                 * amap_swap_off will call us again.
                 */
                amap_unlock(amap);
                return;
        }
        amap_list_remove(amap);
        amap_unlock(amap);

        for (lcv = 0 ; lcv < amap->am_nused ; lcv++) {
                int refs;

                slot = amap->am_slots[lcv];
                anon = amap->am_anon[slot];
                KASSERT(anon != NULL && anon->an_ref != 0);

                mutex_enter(&anon->an_lock);
                UVMHIST_LOG(maphist,"  processing anon 0x%x, ref=%d", anon,
                    anon->an_ref, 0, 0);
                refs = --anon->an_ref;
                mutex_exit(&anon->an_lock);
                if (refs == 0) {

                        /*
                         * we had the last reference to a vm_anon. free it.
                         */

                        uvm_anfree(anon);
                }

                if (curlwp->l_cpu->ci_schedstate.spc_flags & SPCF_SHOULDYIELD)
                        preempt();
        }

        /*
         * now we free the map
         */

        amap->am_nused = 0;
        amap_free(amap);        /* will unlock and 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)
{
        struct vm_amap *amap, *srcamap;
        int slots, lcv;
        vaddr_t chunksize;
        const int waitf = (flags & AMAP_COPY_NOWAIT) ? UVM_FLAG_NOWAIT : 0;
        const bool canchunk = (flags & AMAP_COPY_NOCHUNK) == 0;
        UVMHIST_FUNC("amap_copy"); UVMHIST_CALLED(maphist);
        UVMHIST_LOG(maphist, "  (map=%p, entry=%p, flags=%d)",
                    map, entry, flags, 0);

        KASSERT(map != kernel_map);     /* we use nointr pool */

        /*
         * is there a map to copy?   if not, create one from scratch.
         */

        if (entry->aref.ar_amap == NULL) {

                /*
                 * 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(entry->end - entry->start) >=
                    UVM_AMAP_LARGE) {
                        /* convert slots to bytes */
                        chunksize = UVM_AMAP_CHUNK << PAGE_SHIFT;
                        startva = (startva / chunksize) * chunksize;
                        endva = roundup(endva, chunksize);
                        UVMHIST_LOG(maphist, "  chunk amap ==> clip 0x%x->0x%x"
                            "to 0x%x->0x%x", entry->start, entry->end, startva,
                            endva);
                        UVM_MAP_CLIP_START(map, entry, startva, NULL);
                        /* watch out for endva wrap-around! */
                        if (endva >= startva)
                                UVM_MAP_CLIP_END(map, entry, endva, NULL);
                }

                if ((flags & AMAP_COPY_NOMERGE) == 0 &&
                    uvm_mapent_trymerge(map, entry, UVM_MERGE_COPYING)) {
                        return;
                }

                UVMHIST_LOG(maphist, "<- done [creating new amap 0x%x->0x%x]",
                entry->start, entry->end, 0, 0);
                entry->aref.ar_pageoff = 0;
                entry->aref.ar_amap = amap_alloc(entry->end - entry->start, 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 the amap we currently have.  if so, then we can
         * just take it over rather than copying it.  note that we are
         * reading am_ref with the amap unlocked... the value can only
         * be one if we have the only reference to the amap (via our
         * locked map).  if we are greater than one we fall through to
         * the next case (where we double check the value).
         */

        if (entry->aref.ar_amap->am_ref == 1) {
                entry->etype &= ~UVM_ET_NEEDSCOPY;
                UVMHIST_LOG(maphist, "<- done [ref cnt = 1, took it over]",
                    0, 0, 0, 0);
                return;
        }

        /*
         * looks like we need to copy the map.
         */

        UVMHIST_LOG(maphist,"  amap=%p, ref=%d, must copy it",
            entry->aref.ar_amap, entry->aref.ar_amap->am_ref, 0, 0);
        AMAP_B2SLOT(slots, entry->end - entry->start);
        amap = amap_alloc1(slots, 0, waitf);
        if (amap == NULL) {
                UVMHIST_LOG(maphist, "  amap_alloc1 failed", 0,0,0,0);
                return;
        }
        srcamap = entry->aref.ar_amap;
        amap_lock(srcamap);

        /*
         * need to double check reference count now that we've got the
         * src amap locked down.  the reference count could have
         * changed while we were in malloc.  if the reference count
         * dropped down to one we take over the old map rather than
         * copying the amap.
         */

        if (srcamap->am_ref == 1) {             /* take it over? */
                entry->etype &= ~UVM_ET_NEEDSCOPY;
                amap->am_ref--;         /* drop final reference to map */
                amap_free(amap);        /* dispose of new (unused) amap */
                amap_unlock(srcamap);
                return;
        }

        /*
         * we must copy it now.
         */

        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;
                mutex_enter(&amap->am_anon[lcv]->an_lock);
                amap->am_anon[lcv]->an_ref++;
                mutex_exit(&amap->am_anon[lcv]->an_lock);
                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.
         * we know that the reference count on srcamap is greater than
         * one (we checked above), so there is no way we could drop
         * the count to zero.  [and no need to worry about freeing it]
         */

        srcamap->am_ref--;
        if (srcamap->am_ref == 1 && (srcamap->am_flags & AMAP_SHARED) != 0)
                srcamap->am_flags &= ~AMAP_SHARED;   /* clear shared flag */
#ifdef UVM_AMAP_PPREF
        if (srcamap->am_ppref && srcamap->am_ppref != PPREF_NONE) {
                amap_pp_adjref(srcamap, entry->aref.ar_pageoff,
                    (entry->end - entry->start) >> PAGE_SHIFT, -1);
        }
#endif

        amap_unlock(srcamap);

        amap_list_insert(amap);

        /*
         * 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)
 * => page queues must be unlocked (we may lock them)
 */

void
amap_cow_now(struct vm_map *map, struct vm_map_entry *entry)
{
        struct vm_amap *amap = entry->aref.ar_amap;
        int lcv, slot;
        struct vm_anon *anon, *nanon;
        struct vm_page *pg, *npg;

        /*
         * 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);
        for (lcv = 0 ; lcv < amap->am_nused ; lcv++) {

                /*
                 * get the page
                 */

                slot = amap->am_slots[lcv];
                anon = amap->am_anon[slot];
                mutex_enter(&anon->an_lock);

                /*
                 * If the anon has only one ref, 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 the new page is not wired.
                 */

                if (anon->an_ref == 1) {
                        KASSERT(anon->an_page != NULL || anon->an_swslot != 0);
                        mutex_exit(&anon->an_lock);
                        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) {
                        mutex_exit(&anon->an_lock);
                        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) {
                        pg->flags |= PG_WANTED;
                        amap_unlock(amap);
                        UVM_UNLOCK_AND_WAIT(pg, &anon->an_lock, false,
                            "cownow", 0);
                        goto ReStart;
                }

                /*
                 * ok, time to do a copy-on-write to a new anon
                 */

                nanon = uvm_analloc();
                if (nanon) {
                        npg = uvm_pagealloc(NULL, 0, nanon, 0);
                } else
                        npg = NULL;     /* XXX: quiet gcc warning */
                if (nanon == NULL || npg == NULL) {

                        /*
                         * XXXCDC: we should cause fork to fail, but we can't.
                         */

                        if (nanon) {
                                nanon->an_ref--;
                                mutex_exit(&nanon->an_lock);
                                uvm_anfree(nanon);
                        }
                        mutex_exit(&anon->an_lock);
                        amap_unlock(amap);
                        uvm_wait("cownowpage");
                        goto ReStart;
                }

                /*
                 * got it... now we can copy the data and replace anon
                 * with our new one...
                 */

                uvm_pagecopy(pg, npg);          /* old -> new */
                anon->an_ref--;                 /* can't drop to zero */
                amap->am_anon[slot] = nanon;    /* replace */

                /*
                 * drop PG_BUSY on new page ... since we have had its owner
                 * locked the whole time it can't be PG_RELEASED or PG_WANTED.
                 */

                mutex_enter(&uvm_pageqlock);
                uvm_pageactivate(npg);
                mutex_exit(&uvm_pageqlock);
                npg->flags &= ~(PG_BUSY|PG_FAKE);
                UVM_PAGE_OWN(npg, NULL);
                mutex_exit(&nanon->an_lock);
                mutex_exit(&anon->an_lock);
        }
        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)
{
        int leftslots;
        struct vm_amap *amap;

        KASSERT(splitref->ar_amap == origref->ar_amap);
        AMAP_B2SLOT(leftslots, offset);
        KASSERT(leftslots != 0);

        amap = origref->ar_amap;
        amap_lock(amap);

        /*
         * now: amap is locked and we have a valid am_mapped array.
         */
        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

        amap->am_ref++;         /* not a share reference */
        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 locked by caller
 */
void
amap_pp_establish(struct vm_amap *amap, vaddr_t offset)
{

        amap->am_ppref = kmem_alloc(amap->am_maxslot * sizeof(*amap->am_ppref),
            KM_NOSLEEP);

        /*
         * if we fail then we just won't use ppref for this amap
         */

        if (amap->am_ppref == NULL) {
                amap->am_ppref = PPREF_NONE;    /* not using it */
                return;
        }
        memset(amap->am_ppref, 0, sizeof(int) * amap->am_maxslot);
        pp_setreflen(amap->am_ppref, 0, 0, offset);
        pp_setreflen(amap->am_ppref, offset, amap->am_ref,
            amap->am_nslot - offset);
        return;
}

/*
 * amap_pp_adjref: adjust reference count to a part of an amap using the
 * per-page reference count array.
 *
 * => map and amap locked by caller
 * => caller must check that ppref != PPREF_NONE before calling
 */
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;

        stopslot = curslot + slotlen;
        ppref = amap->am_ppref;
        prevlcv = 0;

        /*
         * first advance to the correct place in the ppref 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)
                pp_getreflen(ppref, prevlcv, &prevref, &prevlen);
        else {
                /* Ensure that the "prevref == ref" test below always
                 * fails, since we're starting from the beginning of
                 * the ppref array; that is, there is no previous
                 * chunk.
                 */
                prevref = -1;
                prevlen = 0;
        }

        /*
         * 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);
                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
 * [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)
{
        int byanon, lcv, stop, curslot, ptr, slotend;
        struct vm_anon *anon;

        /*
         * we can either traverse the amap by am_anon or by am_slots depending
         * on which is cheaper.    decide now.
         */

        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) {
                int refs;

                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];

                /*
                 * remove it from the amap
                 */

                amap->am_anon[curslot] = NULL;
                ptr = amap->am_bckptr[curslot];
                if (ptr != (amap->am_nused - 1)) {
                        amap->am_slots[ptr] =
                            amap->am_slots[amap->am_nused - 1];
                        amap->am_bckptr[amap->am_slots[ptr]] =
                            ptr;    /* back ptr. */
                }
                amap->am_nused--;

                /*
                 * drop anon reference count
                 */

                mutex_enter(&anon->an_lock);
                refs = --anon->an_ref;
                mutex_exit(&anon->an_lock);
                if (refs == 0) {

                        /*
                         * we just eliminated the last reference to an anon.
                         * free it.
                         */

                        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;
        struct lwp *l = curlwp;
        bool rv = false;

#if defined(DIAGNOSTIC)
        memset(&marker_prev, 0, sizeof(marker_prev));
        memset(&marker_next, 0, sizeof(marker_next));
#endif /* defined(DIAGNOSTIC) */

        uvm_lwp_hold(l);
        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);

                if (!amap_lock_try(am)) {
                        mutex_exit(&amap_list_lock);
                        preempt();
                        mutex_enter(&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->am_nused <= 0) {
                        amap_unlock(am);
                        goto next;
                }

                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];
                        mutex_enter(&anon->an_lock);

                        swslot = anon->an_swslot;
                        if (swslot < startslot || endslot <= swslot) {
                                mutex_exit(&anon->an_lock);
                                continue;
                        }

                        am->am_flags |= AMAP_SWAPOFF;
                        amap_unlock(am);

                        rv = uvm_anon_pagein(anon);

                        amap_lock(am);
                        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);
                }
                
next:
                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);
        uvm_lwp_rele(l);

        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_anon *an;
        int slot;
        struct vm_amap *amap = aref->ar_amap;
        UVMHIST_FUNC("amap_lookup"); UVMHIST_CALLED(maphist);
        KASSERT(mutex_owned(&amap->am_l));

        AMAP_B2SLOT(slot, offset);
        slot += aref->ar_pageoff;
        KASSERT(slot < amap->am_nslot);

        UVMHIST_LOG(maphist, "<- done (amap=0x%x, offset=0x%x, result=0x%x)",
            amap, offset, amap->am_anon[slot], 0);
        an = amap->am_anon[slot];
        KASSERT(an == NULL || an->an_ref != 0);
        return an;
}

/*
 * amap_lookups: look up a range of pages in an amap
 *
 * => amap should be locked by caller.
 * => XXXCDC: this interface is biased toward array-based amaps.  fix.
 */
void
amap_lookups(struct vm_aref *aref, vaddr_t offset, struct vm_anon **anons,
    int npages)
{
        int slot;
        struct vm_amap *amap = aref->ar_amap;
#if defined(DIAGNOSTIC)
        int i;
#endif /* defined(DIAGNOSTIC) */
        UVMHIST_FUNC("amap_lookups"); UVMHIST_CALLED(maphist);
        KASSERT(mutex_owned(&amap->am_l));

        AMAP_B2SLOT(slot, offset);
        slot += aref->ar_pageoff;

        UVMHIST_LOG(maphist, "  slot=%d, 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 (i = 0; i < npages; i++) {
                struct vm_anon * const an = anons[i];

                if (an != NULL && an->an_ref == 0) {
                        panic("%s: ref=0 anon", __func__);
                }
        }
#endif /* defined(DIAGNOSTIC) */
        UVMHIST_LOG(maphist, "<- done", 0, 0, 0, 0);
        return;
}

/*
 * amap_add: add (or replace) a page to an amap
 *
 * => caller must lock amap.
 * => if (replace) caller must lock anon because we might have to call
 *      pmap_page_protect on the anon's page.
 */
void
amap_add(struct vm_aref *aref, vaddr_t offset, struct vm_anon *anon,
    bool replace)
{
        int slot;
        struct vm_amap *amap = aref->ar_amap;
        UVMHIST_FUNC("amap_add"); UVMHIST_CALLED(maphist);
        KASSERT(mutex_owned(&amap->am_l));

        AMAP_B2SLOT(slot, offset);
        slot += aref->ar_pageoff;
        KASSERT(slot < amap->am_nslot);

        if (replace) {
                KASSERT(amap->am_anon[slot] != NULL);
                if (amap->am_anon[slot]->an_page != NULL &&
                    (amap->am_flags & AMAP_SHARED) != 0) {
                        pmap_page_protect(amap->am_anon[slot]->an_page,
                            VM_PROT_NONE);
                        /*
                         * XXX: suppose page is supposed to be wired somewhere?
                         */
                }
        } else {   /* !replace */
                KASSERT(amap->am_anon[slot] == NULL);
                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=0x%x, offset=0x%x, anon=0x%x, rep=%d)",
            amap, offset, anon, replace);
}

/*
 * amap_unadd: remove a page from an amap
 *
 * => caller must lock amap
 */
void
amap_unadd(struct vm_aref *aref, vaddr_t offset)
{
        int ptr, slot;
        struct vm_amap *amap = aref->ar_amap;
        UVMHIST_FUNC("amap_unadd"); UVMHIST_CALLED(maphist);
        KASSERT(mutex_owned(&amap->am_l));

        AMAP_B2SLOT(slot, offset);
        slot += aref->ar_pageoff;
        KASSERT(slot < amap->am_nslot);
        KASSERT(amap->am_anon[slot] != NULL);

        amap->am_anon[slot] = NULL;
        ptr = amap->am_bckptr[slot];

        if (ptr != (amap->am_nused - 1)) {      /* swap to keep slots contig? */
                amap->am_slots[ptr] = amap->am_slots[amap->am_nused - 1];
                amap->am_bckptr[amap->am_slots[ptr]] = ptr;     /* back link */
        }
        amap->am_nused--;
        UVMHIST_LOG(maphist, "<- done (amap=0x%x, slot=0x%x)", amap, slot,0, 0);
}

/*
 * 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("amap_ref"); UVMHIST_CALLED(maphist);

        amap_lock(amap);
        if (flags & AMAP_SHARED)
                amap->am_flags |= AMAP_SHARED;
#ifdef UVM_AMAP_PPREF
        if (amap->am_ppref == NULL && (flags & AMAP_REFALL) == 0 &&
            len != amap->am_nslot)
                amap_pp_establish(amap, offset);
#endif
        amap->am_ref++;
#ifdef UVM_AMAP_PPREF
        if (amap->am_ppref && amap->am_ppref != PPREF_NONE) {
                if (flags & AMAP_REFALL)
                        amap_pp_adjref(amap, 0, amap->am_nslot, 1);
                else
                        amap_pp_adjref(amap, offset, len, 1);
        }
#endif
        amap_unlock(amap);
        UVMHIST_LOG(maphist,"<- done!  amap=0x%x", amap, 0, 0, 0);
}

/*
 * amap_unref: remove a reference to an amap
 *
 * => caller must remove all pmap-level references to this amap before
 *      dropping the reference
 * => called from uvm_unmap_detach [only]  ... note that entry is no
 *      longer part of a map and thus has no need for locking
 * => amap must be unlocked (we will lock it).
 */
void
amap_unref(struct vm_amap *amap, vaddr_t offset, vsize_t len, bool all)
{
        UVMHIST_FUNC("amap_unref"); UVMHIST_CALLED(maphist);

        /*
         * lock it
         */
        amap_lock(amap);
        UVMHIST_LOG(maphist,"  amap=0x%x  refs=%d, nused=%d",
            amap, amap->am_ref, amap->am_nused, 0);

        KASSERT(amap_refs(amap) > 0);

        /*
         * if we are the last reference, free the amap and return.
         */

        amap->am_ref--;

        if (amap_refs(amap) == 0) {
                amap_wipeout(amap);     /* drops final ref and frees */
                UVMHIST_LOG(maphist,"<- done (was last ref)!", 0, 0, 0, 0);
                return;                 /* no need to unlock */
        }

        /*
         * otherwise just drop the reference count(s)
         */

        if (amap_refs(amap) == 1 && (amap->am_flags & AMAP_SHARED) != 0)
                amap->am_flags &= ~AMAP_SHARED; /* clear shared flag */
#ifdef UVM_AMAP_PPREF
        if (amap->am_ppref == NULL && all == 0 && len != amap->am_nslot)
                amap_pp_establish(amap, offset);
        if (amap->am_ppref && amap->am_ppref != PPREF_NONE) {
                if (all)
                        amap_pp_adjref(amap, 0, amap->am_nslot, -1);
                else
                        amap_pp_adjref(amap, offset, len, -1);
        }
#endif
        amap_unlock(amap);

        UVMHIST_LOG(maphist,"<- done!", 0, 0, 0, 0);
}