/*      $OpenBSD: uvm_aobj.c,v 1.122 2026/02/11 22:34:40 deraadt Exp $  */
/*      $NetBSD: uvm_aobj.c,v 1.39 2001/02/18 21:19:08 chs Exp $        */

/*
 * Copyright (c) 1998 Chuck Silvers, 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.
 *
 * from: Id: uvm_aobj.c,v 1.1.2.5 1998/02/06 05:14:38 chs Exp
 */
/*
 * uvm_aobj.c: anonymous memory uvm_object pager
 *
 * author: Chuck Silvers <chuq@chuq.com>
 * started: Jan-1998
 *
 * - design mostly from Chuck Cranor
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/kernel.h>
#include <sys/pool.h>
#include <sys/stdint.h>
#include <sys/atomic.h>

#include <uvm/uvm.h>

/*
 * An anonymous UVM object (aobj) manages anonymous-memory.  In addition to
 * keeping the list of resident pages, it may also keep a list of allocated
 * swap blocks.  Depending on the size of the object, this list is either
 * stored in an array (small objects) or in a hash table (large objects).
 */

/*
 * Note: for hash tables, we break the address space of the aobj into blocks
 * of UAO_SWHASH_CLUSTER_SIZE pages, which shall be a power of two.
 */
#define UAO_SWHASH_CLUSTER_SHIFT        4
#define UAO_SWHASH_CLUSTER_SIZE         (1 << UAO_SWHASH_CLUSTER_SHIFT)

/* Get the "tag" for this page index. */
#define UAO_SWHASH_ELT_TAG(idx)         ((idx) >> UAO_SWHASH_CLUSTER_SHIFT)
#define UAO_SWHASH_ELT_PAGESLOT_IDX(idx) \
    ((idx) & (UAO_SWHASH_CLUSTER_SIZE - 1))

/* Given an ELT and a page index, find the swap slot. */
#define UAO_SWHASH_ELT_PAGESLOT(elt, idx) \
    ((elt)->slots[UAO_SWHASH_ELT_PAGESLOT_IDX(idx)])

/* Given an ELT, return its pageidx base. */
#define UAO_SWHASH_ELT_PAGEIDX_BASE(elt) \
    ((elt)->tag << UAO_SWHASH_CLUSTER_SHIFT)

/* The hash function. */
#define UAO_SWHASH_HASH(aobj, idx) \
    (&(aobj)->u_swhash[(((idx) >> UAO_SWHASH_CLUSTER_SHIFT) \
    & (aobj)->u_swhashmask)])

/*
 * The threshold which determines whether we will use an array or a
 * hash table to store the list of allocated swap blocks.
 */
#define UAO_SWHASH_THRESHOLD            (UAO_SWHASH_CLUSTER_SIZE * 4)
#define UAO_USES_SWHASH(aobj) \
    ((aobj)->u_pages > UAO_SWHASH_THRESHOLD)

/* The number of buckets in a hash, with an upper bound. */
#define UAO_SWHASH_MAXBUCKETS           256
#define UAO_SWHASH_BUCKETS(pages) \
    (min((pages) >> UAO_SWHASH_CLUSTER_SHIFT, UAO_SWHASH_MAXBUCKETS))


/*
 * uao_swhash_elt: when a hash table is being used, this structure defines
 * the format of an entry in the bucket list.
 */
struct uao_swhash_elt {
        LIST_ENTRY(uao_swhash_elt) list;        /* the hash list */
        voff_t tag;                             /* our 'tag' */
        int count;                              /* our number of active slots */
        int slots[UAO_SWHASH_CLUSTER_SIZE];     /* the slots */
};

/*
 * uao_swhash: the swap hash table structure
 */
LIST_HEAD(uao_swhash, uao_swhash_elt);

/*
 * uao_swhash_elt_pool: pool of uao_swhash_elt structures
 */
struct pool uao_swhash_elt_pool;

/*
 * uvm_aobj: the actual anon-backed uvm_object
 *
 * => the uvm_object is at the top of the structure, this allows
 *   (struct uvm_aobj *) == (struct uvm_object *)
 * => only one of u_swslots and u_swhash is used in any given aobj
 */
struct uvm_aobj {
        struct uvm_object u_obj; /* has: pgops, memt, #pages, #refs */
        int u_pages;             /* number of pages in entire object */
        int u_flags;             /* the flags (see uvm_aobj.h) */
        /*
         * Either an array or hashtable (array of bucket heads) of
         * offset -> swapslot mappings for the aobj.
         */
#define u_swslots       u_swap.slot_array 
#define u_swhash        u_swap.slot_hash
        union swslots {
                int                     *slot_array;
                struct uao_swhash       *slot_hash;
        } u_swap;
        u_long u_swhashmask;            /* mask for hashtable */
        LIST_ENTRY(uvm_aobj) u_list;    /* global list of aobjs */
};

struct pool uvm_aobj_pool;

static struct uao_swhash_elt    *uao_find_swhash_elt(struct uvm_aobj *, int,
                                     boolean_t, boolean_t);
static boolean_t                 uao_flush(struct uvm_object *, voff_t,
                                     voff_t, int);
static void                      uao_free(struct uvm_aobj *);
static int                       uao_get(struct uvm_object *, voff_t,
                                     vm_page_t *, int *, int, vm_prot_t,
                                     int, int);
static boolean_t                 uao_pagein(struct uvm_aobj *, int, int);
static boolean_t                 uao_pagein_page(struct uvm_aobj *, int);

void    uao_dropswap_range(struct uvm_object *, voff_t, voff_t);
void    uao_shrink_flush(struct uvm_object *, int, int);
int     uao_shrink_hash(struct uvm_object *, int);
int     uao_shrink_array(struct uvm_object *, int);
int     uao_shrink_convert(struct uvm_object *, int);

int     uao_grow_hash(struct uvm_object *, int);
int     uao_grow_array(struct uvm_object *, int);
int     uao_grow_convert(struct uvm_object *, int);

/*
 * aobj_pager
 *
 * note that some functions (e.g. put) are handled elsewhere
 */
const struct uvm_pagerops aobj_pager = {
        .pgo_reference = uao_reference,
        .pgo_detach = uao_detach,
        .pgo_flush = uao_flush,
        .pgo_get = uao_get,
};

/*
 * uao_list: global list of active aobjs, locked by uao_list_lock
 *
 * Lock ordering: generally the locking order is object lock, then list lock.
 * in the case of swap off we have to iterate over the list, and thus the
 * ordering is reversed. In that case we must use trylocking to prevent
 * deadlock.
 */
static LIST_HEAD(aobjlist, uvm_aobj) uao_list = LIST_HEAD_INITIALIZER(uao_list);
static struct mutex uao_list_lock = MUTEX_INITIALIZER(IPL_MPFLOOR);


/*
 * functions
 */
/*
 * hash table/array related functions
 */
/*
 * uao_find_swhash_elt: find (or create) a hash table entry for a page
 * offset.
 */
static struct uao_swhash_elt *
uao_find_swhash_elt(struct uvm_aobj *aobj, int pageidx, boolean_t create,
    boolean_t wait)
{
        struct uao_swhash *swhash;
        struct uao_swhash_elt *elt;
        int waitf = wait ? PR_WAITOK : PR_NOWAIT;
        voff_t page_tag;

        swhash = UAO_SWHASH_HASH(aobj, pageidx); /* first hash to get bucket */
        page_tag = UAO_SWHASH_ELT_TAG(pageidx); /* tag to search for */

        /*
         * now search the bucket for the requested tag
         */
        LIST_FOREACH(elt, swhash, list) {
                if (elt->tag == page_tag)
                        return elt;
        }

        if (!create)
                return NULL;

        /*
         * allocate a new entry for the bucket and init/insert it in
         */
        elt = pool_get(&uao_swhash_elt_pool, waitf | PR_ZERO);
        if (elt == NULL)
                return NULL;
        LIST_INSERT_HEAD(swhash, elt, list);
        elt->tag = page_tag;

        return elt;
}

/*
 * uao_find_swslot: find the swap slot number for an aobj/pageidx
 */
int
uao_find_swslot(struct uvm_object *uobj, int pageidx)
{
        struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;

        KASSERT(UVM_OBJ_IS_AOBJ(uobj));

        /*
         * if noswap flag is set, then we never return a slot
         */
        if (aobj->u_flags & UAO_FLAG_NOSWAP)
                return 0;

        /*
         * if hashing, look in hash table.
         */
        if (UAO_USES_SWHASH(aobj)) {
                struct uao_swhash_elt *elt =
                    uao_find_swhash_elt(aobj, pageidx, FALSE, FALSE);

                if (elt)
                        return UAO_SWHASH_ELT_PAGESLOT(elt, pageidx);
                else
                        return 0;
        }

        /*
         * otherwise, look in the array
         */
        return aobj->u_swslots[pageidx];
}

/*
 * uao_set_swslot: set the swap slot for a page in an aobj.
 *
 * => setting a slot to zero frees the slot
 * => object must be locked by caller
 * => we return the old slot number, or -1 if we failed to allocate
 *    memory to record the new slot number
 */
int
uao_set_swslot(struct uvm_object *uobj, int pageidx, int slot)
{
        struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
        struct uao_swhash_elt *elt;
        int oldslot;

        KASSERT(rw_write_held(uobj->vmobjlock) || uobj->uo_refs == 0);
        KASSERT(UVM_OBJ_IS_AOBJ(uobj));

        /*
         * if noswap flag is set, then we can't set a slot
         */
        if (aobj->u_flags & UAO_FLAG_NOSWAP) {
                if (slot == 0)
                        return 0;               /* a clear is ok */

                /* but a set is not */
                printf("uao_set_swslot: uobj = %p\n", uobj);
                panic("uao_set_swslot: attempt to set a slot on a NOSWAP object");
        }

        /*
         * are we using a hash table?  if so, add it in the hash.
         */
        if (UAO_USES_SWHASH(aobj)) {
                /*
                 * Avoid allocating an entry just to free it again if
                 * the page had not swap slot in the first place, and
                 * we are freeing.
                 */
                elt = uao_find_swhash_elt(aobj, pageidx, slot != 0, FALSE);
                if (elt == NULL) {
                        return slot ? - 1 : 0;
                }

                oldslot = UAO_SWHASH_ELT_PAGESLOT(elt, pageidx);
                UAO_SWHASH_ELT_PAGESLOT(elt, pageidx) = slot;

                /*
                 * now adjust the elt's reference counter and free it if we've
                 * dropped it to zero.
                 */
                if (slot) {
                        if (oldslot == 0)
                                elt->count++;
                } else {
                        if (oldslot)
                                elt->count--;

                        if (elt->count == 0) {
                                LIST_REMOVE(elt, list);
                                pool_put(&uao_swhash_elt_pool, elt);
                        }
                }
        } else {
                /* we are using an array */
                oldslot = aobj->u_swslots[pageidx];
                aobj->u_swslots[pageidx] = slot;
        }
        return oldslot;
}
/*
 * end of hash/array functions
 */

/*
 * uao_free: free all resources held by an aobj, and then free the aobj
 *
 * => the aobj should be dead
 */
static void
uao_free(struct uvm_aobj *aobj)
{
        struct uvm_object *uobj = &aobj->u_obj;

        KASSERT(UVM_OBJ_IS_AOBJ(uobj));
        KASSERT(rw_write_held(uobj->vmobjlock));
        uao_dropswap_range(uobj, 0, 0);
        rw_exit(uobj->vmobjlock);

        if (UAO_USES_SWHASH(aobj)) {
                /*
                 * free the hash table itself.
                 */
                hashfree(aobj->u_swhash, UAO_SWHASH_BUCKETS(aobj->u_pages), M_UVMAOBJ);
        } else {
                free(aobj->u_swslots, M_UVMAOBJ, aobj->u_pages * sizeof(int));
        }

        /*
         * finally free the aobj itself
         */
        uvm_obj_destroy(uobj);
        pool_put(&uvm_aobj_pool, aobj);
}

/*
 * pager functions
 */

#ifdef TMPFS
/*
 * Shrink an aobj to a given number of pages. The procedure is always the same:
 * assess the necessity of data structure conversion (hash to array), secure
 * resources, flush pages and drop swap slots.
 *
 */

void
uao_shrink_flush(struct uvm_object *uobj, int startpg, int endpg)
{
        KASSERT(startpg < endpg);
        KASSERT(uobj->uo_refs == 1);
        uao_flush(uobj, (voff_t)startpg << PAGE_SHIFT,
            (voff_t)endpg << PAGE_SHIFT, PGO_FREE);
        uao_dropswap_range(uobj, startpg, endpg);
}

int
uao_shrink_hash(struct uvm_object *uobj, int pages)
{
        struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
        struct uao_swhash *new_swhash;
        struct uao_swhash_elt *elt;
        unsigned long new_hashmask;
        int i;

        KASSERT(UAO_USES_SWHASH(aobj));

        /*
         * If the size of the hash table doesn't change, all we need to do is
         * to adjust the page count.
         */
        if (UAO_SWHASH_BUCKETS(aobj->u_pages) == UAO_SWHASH_BUCKETS(pages)) {
                uao_shrink_flush(uobj, pages, aobj->u_pages);
                aobj->u_pages = pages;
                return 0;
        }

        new_swhash = hashinit(UAO_SWHASH_BUCKETS(pages), M_UVMAOBJ,
            M_WAITOK | M_CANFAIL, &new_hashmask);
        if (new_swhash == NULL)
                return ENOMEM;

        uao_shrink_flush(uobj, pages, aobj->u_pages);

        /*
         * Even though the hash table size is changing, the hash of the buckets
         * we are interested in copying should not change.
         */
        for (i = 0; i < UAO_SWHASH_BUCKETS(aobj->u_pages); i++) {
                while (LIST_EMPTY(&aobj->u_swhash[i]) == 0) {
                        elt = LIST_FIRST(&aobj->u_swhash[i]);
                        LIST_REMOVE(elt, list);
                        LIST_INSERT_HEAD(&new_swhash[i], elt, list);
                }
        }

        hashfree(aobj->u_swhash, UAO_SWHASH_BUCKETS(aobj->u_pages), M_UVMAOBJ);

        aobj->u_swhash = new_swhash;
        aobj->u_pages = pages;
        aobj->u_swhashmask = new_hashmask;

        return 0;
}

int
uao_shrink_convert(struct uvm_object *uobj, int pages)
{
        struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
        struct uao_swhash_elt *elt;
        int i, *new_swslots;

        new_swslots = mallocarray(pages, sizeof(int), M_UVMAOBJ,
            M_WAITOK | M_CANFAIL | M_ZERO);
        if (new_swslots == NULL)
                return ENOMEM;

        uao_shrink_flush(uobj, pages, aobj->u_pages);

        /* Convert swap slots from hash to array.  */
        for (i = 0; i < pages; i++) {
                elt = uao_find_swhash_elt(aobj, i, FALSE, FALSE);
                if (elt != NULL) {
                        new_swslots[i] = UAO_SWHASH_ELT_PAGESLOT(elt, i);
                        if (new_swslots[i] != 0)
                                elt->count--;
                        if (elt->count == 0) {
                                LIST_REMOVE(elt, list);
                                pool_put(&uao_swhash_elt_pool, elt);
                        }
                }
        }

        hashfree(aobj->u_swhash, UAO_SWHASH_BUCKETS(aobj->u_pages), M_UVMAOBJ);

        aobj->u_swslots = new_swslots;
        aobj->u_pages = pages;

        return 0;
}

int
uao_shrink_array(struct uvm_object *uobj, int pages)
{
        struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
        int i, *new_swslots;

        new_swslots = mallocarray(pages, sizeof(int), M_UVMAOBJ,
            M_WAITOK | M_CANFAIL | M_ZERO);
        if (new_swslots == NULL)
                return ENOMEM;

        uao_shrink_flush(uobj, pages, aobj->u_pages);

        for (i = 0; i < pages; i++)
                new_swslots[i] = aobj->u_swslots[i];

        free(aobj->u_swslots, M_UVMAOBJ, aobj->u_pages * sizeof(int));

        aobj->u_swslots = new_swslots;
        aobj->u_pages = pages;

        return 0;
}

int
uao_shrink(struct uvm_object *uobj, int pages)
{
        struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;

        KASSERT(pages < aobj->u_pages);

        /*
         * Distinguish between three possible cases:
         * 1. aobj uses hash and must be converted to array.
         * 2. aobj uses array and array size needs to be adjusted.
         * 3. aobj uses hash and hash size needs to be adjusted.
         */
        if (pages > UAO_SWHASH_THRESHOLD)
                return uao_shrink_hash(uobj, pages);    /* case 3 */
        else if (aobj->u_pages > UAO_SWHASH_THRESHOLD)
                return uao_shrink_convert(uobj, pages); /* case 1 */
        else
                return uao_shrink_array(uobj, pages);   /* case 2 */
}

/*
 * Grow an aobj to a given number of pages. Right now we only adjust the swap
 * slots. We could additionally handle page allocation directly, so that they
 * don't happen through uvm_fault(). That would allow us to use another
 * mechanism for the swap slots other than malloc(). It is thus mandatory that
 * the caller of these functions does not allow faults to happen in case of
 * growth error.
 */
int
uao_grow_array(struct uvm_object *uobj, int pages)
{
        struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
        int i, *new_swslots;

        KASSERT(aobj->u_pages <= UAO_SWHASH_THRESHOLD);

        new_swslots = mallocarray(pages, sizeof(int), M_UVMAOBJ,
            M_WAITOK | M_CANFAIL | M_ZERO);
        if (new_swslots == NULL)
                return ENOMEM;

        for (i = 0; i < aobj->u_pages; i++)
                new_swslots[i] = aobj->u_swslots[i];

        free(aobj->u_swslots, M_UVMAOBJ, aobj->u_pages * sizeof(int));

        aobj->u_swslots = new_swslots;
        aobj->u_pages = pages;

        return 0;
}

int
uao_grow_hash(struct uvm_object *uobj, int pages)
{
        struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
        struct uao_swhash *new_swhash;
        struct uao_swhash_elt *elt;
        unsigned long new_hashmask;
        int i;

        KASSERT(pages > UAO_SWHASH_THRESHOLD);

        /*
         * If the size of the hash table doesn't change, all we need to do is
         * to adjust the page count.
         */
        if (UAO_SWHASH_BUCKETS(aobj->u_pages) == UAO_SWHASH_BUCKETS(pages)) {
                aobj->u_pages = pages;
                return 0;
        }

        KASSERT(UAO_SWHASH_BUCKETS(aobj->u_pages) < UAO_SWHASH_BUCKETS(pages));

        new_swhash = hashinit(UAO_SWHASH_BUCKETS(pages), M_UVMAOBJ,
            M_WAITOK | M_CANFAIL, &new_hashmask);
        if (new_swhash == NULL)
                return ENOMEM;

        for (i = 0; i < UAO_SWHASH_BUCKETS(aobj->u_pages); i++) {
                while (LIST_EMPTY(&aobj->u_swhash[i]) == 0) {
                        elt = LIST_FIRST(&aobj->u_swhash[i]);
                        LIST_REMOVE(elt, list);
                        LIST_INSERT_HEAD(&new_swhash[i], elt, list);
                }
        }

        hashfree(aobj->u_swhash, UAO_SWHASH_BUCKETS(aobj->u_pages), M_UVMAOBJ);

        aobj->u_swhash = new_swhash;
        aobj->u_pages = pages;
        aobj->u_swhashmask = new_hashmask;

        return 0;
}

int
uao_grow_convert(struct uvm_object *uobj, int pages)
{
        struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
        struct uao_swhash *new_swhash;
        struct uao_swhash_elt *elt;
        unsigned long new_hashmask;
        int i, *old_swslots;

        new_swhash = hashinit(UAO_SWHASH_BUCKETS(pages), M_UVMAOBJ,
            M_WAITOK | M_CANFAIL, &new_hashmask);
        if (new_swhash == NULL)
                return ENOMEM;

        /* Set these now, so we can use uao_find_swhash_elt(). */
        old_swslots = aobj->u_swslots;
        aobj->u_swhash = new_swhash;
        aobj->u_swhashmask = new_hashmask;

        for (i = 0; i < aobj->u_pages; i++) {
                if (old_swslots[i] != 0) {
                        elt = uao_find_swhash_elt(aobj, i, TRUE, TRUE);
                        elt->count++;
                        UAO_SWHASH_ELT_PAGESLOT(elt, i) = old_swslots[i];
                }
        }

        free(old_swslots, M_UVMAOBJ, aobj->u_pages * sizeof(int));
        aobj->u_pages = pages;

        return 0;
}

int
uao_grow(struct uvm_object *uobj, int pages)
{
        struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;

        KASSERT(pages > aobj->u_pages);

        /*
         * Distinguish between three possible cases:
         * 1. aobj uses hash and hash size needs to be adjusted.
         * 2. aobj uses array and array size needs to be adjusted.
         * 3. aobj uses array and must be converted to hash.
         */
        if (pages <= UAO_SWHASH_THRESHOLD)
                return uao_grow_array(uobj, pages);     /* case 2 */
        else if (aobj->u_pages > UAO_SWHASH_THRESHOLD)
                return uao_grow_hash(uobj, pages);      /* case 1 */
        else
                return uao_grow_convert(uobj, pages);
}
#endif /* TMPFS */

/*
 * uao_create: create an aobj of the given size and return its uvm_object.
 *
 * => for normal use, flags are zero or UAO_FLAG_CANFAIL.
 * => for the kernel object, the flags are:
 *      UAO_FLAG_KERNOBJ - allocate the kernel object (can only happen once)
 *      UAO_FLAG_KERNSWAP - enable swapping of kernel object ("           ")
 */
struct uvm_object *
uao_create(vsize_t size, int flags)
{
        static struct uvm_aobj kernel_object_store;
        static struct rwlock bootstrap_kernel_object_lock;
        static int kobj_alloced = 0;
        int pages = round_page(size) >> PAGE_SHIFT;
        struct uvm_aobj *aobj;
        int refs;

        /*
         * Allocate a new aobj, unless kernel object is requested.
         */
        if (flags & UAO_FLAG_KERNOBJ) {
                KASSERT(!kobj_alloced);
                aobj = &kernel_object_store;
                aobj->u_pages = pages;
                aobj->u_flags = UAO_FLAG_NOSWAP;
                refs = UVM_OBJ_KERN;
                kobj_alloced = UAO_FLAG_KERNOBJ;
        } else if (flags & UAO_FLAG_KERNSWAP) {
                KASSERT(kobj_alloced == UAO_FLAG_KERNOBJ);
                aobj = &kernel_object_store;
                kobj_alloced = UAO_FLAG_KERNSWAP;
        } else {
                aobj = pool_get(&uvm_aobj_pool, PR_WAITOK);
                aobj->u_pages = pages;
                aobj->u_flags = 0;
                refs = 1;
        }

        /*
         * allocate hash/array if necessary
         */
        if (flags == 0 || (flags & (UAO_FLAG_KERNSWAP | UAO_FLAG_CANFAIL))) {
                int mflags;

                if (flags)
                        mflags = M_NOWAIT;
                else
                        mflags = M_WAITOK;

                /* allocate hash table or array depending on object size */
                if (UAO_USES_SWHASH(aobj)) {
                        aobj->u_swhash = hashinit(UAO_SWHASH_BUCKETS(pages),
                            M_UVMAOBJ, mflags, &aobj->u_swhashmask);
                        if (aobj->u_swhash == NULL) {
                                if (flags & UAO_FLAG_CANFAIL) {
                                        pool_put(&uvm_aobj_pool, aobj);
                                        return NULL;
                                }
                                panic("uao_create: hashinit swhash failed");
                        }
                } else {
                        aobj->u_swslots = mallocarray(pages, sizeof(int),
                            M_UVMAOBJ, mflags|M_ZERO);
                        if (aobj->u_swslots == NULL) {
                                if (flags & UAO_FLAG_CANFAIL) {
                                        pool_put(&uvm_aobj_pool, aobj);
                                        return NULL;
                                }
                                panic("uao_create: malloc swslots failed");
                        }
                }

                if (flags & UAO_FLAG_KERNSWAP) {
                        aobj->u_flags &= ~UAO_FLAG_NOSWAP; /* clear noswap */
                        return &aobj->u_obj;
                        /* done! */
                }
        }

        /*
         * Initialise UVM object.
         */
        uvm_obj_init(&aobj->u_obj, &aobj_pager, refs);
        if (flags & UAO_FLAG_KERNOBJ) {
                /* Use a temporary static lock for kernel_object. */
                rw_init(&bootstrap_kernel_object_lock, "kobjlk");
                uvm_obj_setlock(&aobj->u_obj, &bootstrap_kernel_object_lock);
        }

        /*
         * now that aobj is ready, add it to the global list
         */
        mtx_enter(&uao_list_lock);
        LIST_INSERT_HEAD(&uao_list, aobj, u_list);
        mtx_leave(&uao_list_lock);

        return &aobj->u_obj;
}



/*
 * uao_init: set up aobj pager subsystem
 *
 * => called at boot time from uvm_pager_init()
 */
void
uao_init(void)
{
        /*
         * NOTE: Pages for this pool must not come from a pageable
         * kernel map!
         */
        pool_init(&uao_swhash_elt_pool, sizeof(struct uao_swhash_elt), 0,
            IPL_NONE, PR_WAITOK, "uaoeltpl", NULL);
        pool_init(&uvm_aobj_pool, sizeof(struct uvm_aobj), 0,
            IPL_NONE, PR_WAITOK, "aobjpl", NULL);
}

/*
 * uao_reference: hold a reference to an anonymous UVM object.
 */
void
uao_reference(struct uvm_object *uobj)
{
        /* Kernel object is persistent. */
        if (UVM_OBJ_IS_KERN_OBJECT(uobj))
                return;

        atomic_inc_int(&uobj->uo_refs);
}


/*
 * uao_detach: drop a reference to an anonymous UVM object.
 */
void
uao_detach(struct uvm_object *uobj)
{
        struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
        struct vm_page *pg;

        /*
         * Detaching from kernel_object is a NOP.
         */
        if (UVM_OBJ_IS_KERN_OBJECT(uobj))
                return;

        /*
         * Drop the reference.  If it was the last one, destroy the object.
         */
        if (atomic_dec_int_nv(&uobj->uo_refs) > 0) {
                return;
        }

        /*
         * Remove the aobj from the global list.
         */
        mtx_enter(&uao_list_lock);
        LIST_REMOVE(aobj, u_list);
        mtx_leave(&uao_list_lock);

        /*
         * Free all the pages left in the aobj.  For each page, when the
         * page is no longer busy (and thus after any disk I/O that it is
         * involved in is complete), release any swap resources and free
         * the page itself.
         */
        rw_enter(uobj->vmobjlock, RW_WRITE);
        while ((pg = RBT_ROOT(uvm_objtree, &uobj->memt)) != NULL) {
                pmap_page_protect(pg, PROT_NONE);
                if (pg->pg_flags & PG_BUSY) {
                        uvm_pagewait(pg, uobj->vmobjlock, "uao_det");
                        rw_enter(uobj->vmobjlock, RW_WRITE);
                        continue;
                }
                uao_dropswap(&aobj->u_obj, pg->offset >> PAGE_SHIFT);
                uvm_pagefree(pg);
        }

        /*
         * Finally, free the anonymous UVM object itself.
         */
        uao_free(aobj);
}

/*
 * uao_flush: flush pages out of a uvm object
 *
 * => if PGO_CLEANIT is not set, then we will not block.
 * => if PGO_ALLPAGE is set, then all pages in the object are valid targets
 *      for flushing.
 * => NOTE: we are allowed to lock the page queues, so the caller
 *      must not be holding the lock on them [e.g. pagedaemon had
 *      better not call us with the queues locked]
 * => we return TRUE unless we encountered some sort of I/O error
 *      XXXJRT currently never happens, as we never directly initiate
 *      XXXJRT I/O
 */
boolean_t
uao_flush(struct uvm_object *uobj, voff_t start, voff_t stop, int flags)
{
        struct uvm_aobj *aobj = (struct uvm_aobj *) uobj;
        struct vm_page *pg;
        voff_t curoff;

        KASSERT(UVM_OBJ_IS_AOBJ(uobj));
        KASSERT(rw_write_held(uobj->vmobjlock));

        if (flags & PGO_ALLPAGES) {
                start = 0;
                stop = (voff_t)aobj->u_pages << PAGE_SHIFT;
        } else {
                start = trunc_page(start);
                stop = round_page(stop);
                if (stop > ((voff_t)aobj->u_pages << PAGE_SHIFT)) {
                        printf("uao_flush: strange, got an out of range "
                            "flush (fixed)\n");
                        stop = (voff_t)aobj->u_pages << PAGE_SHIFT;
                }
        }

        /*
         * Don't need to do any work here if we're not freeing
         * or deactivating pages.
         */
        if ((flags & (PGO_DEACTIVATE|PGO_FREE)) == 0) {
                return TRUE;
        }

        curoff = start;
        for (;;) {
                if (curoff < stop) {
                        pg = uvm_pagelookup(uobj, curoff);
                        curoff += PAGE_SIZE;
                        if (pg == NULL)
                                continue;
                } else {
                        break;
                }

                /* Make sure page is unbusy, else wait for it. */
                if (pg->pg_flags & PG_BUSY) {
                        uvm_pagewait(pg, uobj->vmobjlock, "uaoflsh");
                        rw_enter(uobj->vmobjlock, RW_WRITE);
                        curoff -= PAGE_SIZE;
                        continue;
                }

                switch (flags & (PGO_CLEANIT|PGO_FREE|PGO_DEACTIVATE)) {
                /*
                 * XXX In these first 3 cases, we always just
                 * XXX deactivate the page.  We may want to
                 * XXX handle the different cases more specifically
                 * XXX in the future.
                 */
                case PGO_CLEANIT|PGO_FREE:
                case PGO_CLEANIT|PGO_DEACTIVATE:
                case PGO_DEACTIVATE:
 deactivate_it:
                        uvm_pagedeactivate(pg);
                        continue;
                case PGO_FREE:
                        /*
                         * If there are multiple references to
                         * the object, just deactivate the page.
                         */
                        if (uobj->uo_refs > 1)
                                goto deactivate_it;

                        /* XXX skip the page if it's wired */
                        if (pg->wire_count != 0)
                                continue;

                        /*
                         * free the swap slot and the page.
                         */
                        pmap_page_protect(pg, PROT_NONE);

                        /*
                         * freeing swapslot here is not strictly necessary.
                         * however, leaving it here doesn't save much
                         * because we need to update swap accounting anyway.
                         */
                        uao_dropswap(uobj, pg->offset >> PAGE_SHIFT);
                        uvm_pagefree(pg);
                        continue;
                default:
                        panic("uao_flush: weird flags");
                }
        }

        return TRUE;
}

/*
 * uao_get: fetch me a page
 *
 * we have three cases:
 * 1: page is resident     -> just return the page.
 * 2: page is zero-fill    -> allocate a new page and zero it.
 * 3: page is swapped out  -> fetch the page from swap.
 *
 * cases 1 can be handled with PGO_LOCKED, cases 2 and 3 cannot.
 * so, if the "center" page hits case 3 (or any page, with PGO_ALLPAGES),
 * then we will need to return VM_PAGER_UNLOCK.
 *
 * => flags: PGO_ALLPAGES: get all of the pages
 *           PGO_LOCKED: fault data structures are locked
 * => NOTE: offset is the offset of pps[0], _NOT_ pps[centeridx]
 * => NOTE: caller must check for released pages!!
 */
static int
uao_get(struct uvm_object *uobj, voff_t offset, struct vm_page **pps,
    int *npagesp, int centeridx, vm_prot_t access_type, int advice, int flags)
{
        struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
        voff_t current_offset;
        vm_page_t ptmp;
        int lcv, gotpages, maxpages, swslot, rv, pageidx;
        boolean_t done;

        KASSERT(UVM_OBJ_IS_AOBJ(uobj));
        KASSERT(rw_lock_held(uobj->vmobjlock));
        KASSERT(rw_write_held(uobj->vmobjlock) ||
            ((flags & PGO_LOCKED) != 0 && (access_type & PROT_WRITE) == 0));

        /*
         * get number of pages
         */
        maxpages = *npagesp;

        if (flags & PGO_LOCKED) {
                /*
                 * step 1a: get pages that are already resident.   only do
                 * this if the data structures are locked (i.e. the first
                 * time through).
                 */
                done = TRUE;    /* be optimistic */
                gotpages = 0;   /* # of pages we got so far */

                for (lcv = 0, current_offset = offset ; lcv < maxpages ;
                    lcv++, current_offset += PAGE_SIZE) {
                        /* do we care about this page?  if not, skip it */
                        if (pps[lcv] == PGO_DONTCARE)
                                continue;

                        /* lookup page */
                        ptmp = uvm_pagelookup(uobj, current_offset);

                        /*
                         * to be useful must get a non-busy page
                         */
                        if (ptmp == NULL || (ptmp->pg_flags & PG_BUSY) != 0) {
                                if (lcv == centeridx) {
                                        /* need to do a wait or I/O! */
                                        done = FALSE;
                                }
                                if ((flags & PGO_ALLPAGES) != 0) {
                                        done = FALSE;
                                        break;
                                }
                                continue;
                        }

                        /*
                         * useful page: plug it in our result array
                         */
                        pps[lcv] = ptmp;
                        gotpages++;
                }

                /*
                 * step 1b: now we've either done everything needed or we
                 * to unlock and do some waiting or I/O.
                 */
                *npagesp = gotpages;
                return done ? VM_PAGER_OK : VM_PAGER_UNLOCK;
        }

        /*
         * step 2: get non-resident or busy pages.
         * data structures are unlocked.
         */
        for (lcv = 0, current_offset = offset ; lcv < maxpages ;
            lcv++, current_offset += PAGE_SIZE) {
                /*
                 * - skip over pages we've already gotten or don't want
                 * - skip over pages we don't _have_ to get
                 */
                if (pps[lcv] != NULL ||
                    (lcv != centeridx && (flags & PGO_ALLPAGES) == 0))
                        continue;

                pageidx = current_offset >> PAGE_SHIFT;

                /*
                 * we have yet to locate the current page (pps[lcv]).   we
                 * first look for a page that is already at the current offset.
                 * if we find a page, we check to see if it is busy or
                 * released.  if that is the case, then we sleep on the page
                 * until it is no longer busy or released and repeat the lookup.
                 * if the page we found is neither busy nor released, then we
                 * busy it (so we own it) and plug it into pps[lcv].   this
                 * 'break's the following while loop and indicates we are
                 * ready to move on to the next page in the "lcv" loop above.
                 *
                 * if we exit the while loop with pps[lcv] still set to NULL,
                 * then it means that we allocated a new busy/fake/clean page
                 * ptmp in the object and we need to do I/O to fill in the data.
                 */

                /* top of "pps" while loop */
                while (pps[lcv] == NULL) {
                        /* look for a resident page */
                        ptmp = uvm_pagelookup(uobj, current_offset);

                        /* not resident?   allocate one now (if we can) */
                        if (ptmp == NULL) {

                                ptmp = uvm_pagealloc(uobj, current_offset,
                                    NULL, 0);

                                /* out of RAM? */
                                if (ptmp == NULL) {
                                        rw_exit(uobj->vmobjlock);
                                        uvm_wait("uao_getpage");
                                        rw_enter(uobj->vmobjlock, RW_WRITE);
                                        /* goto top of pps while loop */
                                        continue;
                                }

                                /*
                                 * safe with PQ's unlocked: because we just
                                 * alloc'd the page
                                 */
                                atomic_setbits_int(&ptmp->pg_flags, PQ_AOBJ);

                                /* 
                                 * got new page ready for I/O.  break pps while
                                 * loop.  pps[lcv] is still NULL.
                                 */
                                break;
                        }

                        /* page is there, see if we need to wait on it */
                        if ((ptmp->pg_flags & PG_BUSY) != 0) {
                                uvm_pagewait(ptmp, uobj->vmobjlock, "uao_get");
                                rw_enter(uobj->vmobjlock, RW_WRITE);
                                continue;       /* goto top of pps while loop */
                        }

                        /*
                         * if we get here then the page is resident and
                         * unbusy.  we busy it now (so we own it).
                         */
                        /* we own it, caller must un-busy */
                        atomic_setbits_int(&ptmp->pg_flags, PG_BUSY);
                        UVM_PAGE_OWN(ptmp, "uao_get2");
                        pps[lcv] = ptmp;
                }

                /*
                 * if we own the valid page at the correct offset, pps[lcv] will
                 * point to it.   nothing more to do except go to the next page.
                 */
                if (pps[lcv])
                        continue;                       /* next lcv */

                /*
                 * we have a "fake/busy/clean" page that we just allocated.  
                 * do the needed "i/o", either reading from swap or zeroing.
                 */
                swslot = uao_find_swslot(uobj, pageidx);

                /* just zero the page if there's nothing in swap.  */
                if (swslot == 0) {
                        /* page hasn't existed before, just zero it. */
                        uvm_pagezero(ptmp);
                } else {
                        /*
                         * page in the swapped-out page.
                         * unlock object for i/o, relock when done.
                         */

                        rw_exit(uobj->vmobjlock);
                        rv = uvm_swap_get(ptmp, swslot, PGO_SYNCIO);
                        rw_enter(uobj->vmobjlock, RW_WRITE);

                        /*
                         * I/O done.  check for errors.
                         */
                        if (rv != VM_PAGER_OK) {
                                /*
                                 * remove the swap slot from the aobj
                                 * and mark the aobj as having no real slot.
                                 * don't free the swap slot, thus preventing
                                 * it from being used again.
                                 */
                                swslot = uao_set_swslot(&aobj->u_obj, pageidx,
                                                        SWSLOT_BAD);
                                uvm_swap_markbad(swslot, 1);

                                if (ptmp->pg_flags & PG_WANTED)
                                        wakeup(ptmp);
                                atomic_clearbits_int(&ptmp->pg_flags,
                                    PG_WANTED|PG_BUSY);
                                UVM_PAGE_OWN(ptmp, NULL);
                                uvm_pagefree(ptmp);
                                rw_exit(uobj->vmobjlock);

                                return rv;
                        }
                }

                /*
                 * we got the page!   clear the fake flag (indicates valid
                 * data now in page) and plug into our result array.   note
                 * that page is still busy.
                 *
                 * it is the callers job to:
                 * => check if the page is released
                 * => unbusy the page
                 * => activate the page
                 */
                atomic_clearbits_int(&ptmp->pg_flags, PG_FAKE);
                pmap_clear_modify(ptmp);                /* ... and clean */
                pps[lcv] = ptmp;

        }       /* lcv loop */

        rw_exit(uobj->vmobjlock);
        return VM_PAGER_OK;
}

/*
 * uao_dropswap:  release any swap resources from this aobj page.
 *
 * => aobj must be locked or have a reference count of 0.
 */
int
uao_dropswap(struct uvm_object *uobj, int pageidx)
{
        int slot;

        KASSERT(UVM_OBJ_IS_AOBJ(uobj));

        slot = uao_set_swslot(uobj, pageidx, 0);
        if (slot) {
                uvm_swap_free(slot, 1);
        }
        return slot;
}

/*
 * page in every page in every aobj that is paged-out to a range of swslots.
 * 
 * => aobj must be locked and is returned locked.
 * => returns TRUE if pagein was aborted due to lack of memory.
 */
boolean_t
uao_swap_off(int startslot, int endslot)
{
        struct uvm_aobj *aobj;

        /*
         * Walk the list of all anonymous UVM objects.  Grab the first.
         */
        mtx_enter(&uao_list_lock);
        if ((aobj = LIST_FIRST(&uao_list)) == NULL) {
                mtx_leave(&uao_list_lock);
                return FALSE;
        }
        uao_reference(&aobj->u_obj);

        do {
                struct uvm_aobj *nextaobj;
                boolean_t rv;

                /*
                 * Prefetch the next object and immediately hold a reference
                 * on it, so neither the current nor the next entry could
                 * disappear while we are iterating.
                 */
                if ((nextaobj = LIST_NEXT(aobj, u_list)) != NULL) {
                        uao_reference(&nextaobj->u_obj);
                }
                mtx_leave(&uao_list_lock);

                /*
                 * Page in all pages in the swap slot range.
                 */
                rw_enter(aobj->u_obj.vmobjlock, RW_WRITE);
                rv = uao_pagein(aobj, startslot, endslot);
                rw_exit(aobj->u_obj.vmobjlock);

                /* Drop the reference of the current object. */
                uao_detach(&aobj->u_obj);
                if (rv) {
                        if (nextaobj) {
                                uao_detach(&nextaobj->u_obj);
                        }
                        return rv;
                }

                aobj = nextaobj;
                mtx_enter(&uao_list_lock);
        } while (aobj);

        /*
         * done with traversal, unlock the list
         */
        mtx_leave(&uao_list_lock);
        return FALSE;
}

/*
 * page in any pages from aobj in the given range.
 *
 * => returns TRUE if pagein was aborted due to lack of memory.
 */
static boolean_t
uao_pagein(struct uvm_aobj *aobj, int startslot, int endslot)
{
        boolean_t rv;

        if (UAO_USES_SWHASH(aobj)) {
                struct uao_swhash_elt *elt;
                int bucket;

restart:
                for (bucket = aobj->u_swhashmask; bucket >= 0; bucket--) {
                        for (elt = LIST_FIRST(&aobj->u_swhash[bucket]);
                             elt != NULL;
                             elt = LIST_NEXT(elt, list)) {
                                int i;

                                for (i = 0; i < UAO_SWHASH_CLUSTER_SIZE; i++) {
                                        int slot = elt->slots[i];

                                        /*
                                         * if the slot isn't in range, skip it.
                                         */
                                        if (slot < startslot ||
                                            slot >= endslot) {
                                                continue;
                                        }

                                        /*
                                         * process the page,
                                         * the start over on this object
                                         * since the swhash elt
                                         * may have been freed.
                                         */
                                        rv = uao_pagein_page(aobj,
                                          UAO_SWHASH_ELT_PAGEIDX_BASE(elt) + i);
                                        if (rv) {
                                                return rv;
                                        }
                                        goto restart;
                                }
                        }
                }
        } else {
                int i;

                for (i = 0; i < aobj->u_pages; i++) {
                        int slot = aobj->u_swslots[i];

                        /*
                         * if the slot isn't in range, skip it
                         */
                        if (slot < startslot || slot >= endslot) {
                                continue;
                        }

                        /*
                         * process the page.
                         */
                        rv = uao_pagein_page(aobj, i);
                        if (rv) {
                                return rv;
                        }
                }
        }

        return FALSE;
}

/*
 * uao_pagein_page: page in a single page from an anonymous UVM object.
 *
 * => Returns TRUE if pagein was aborted due to lack of memory.
 */
static boolean_t
uao_pagein_page(struct uvm_aobj *aobj, int pageidx)
{
        struct uvm_object *uobj = &aobj->u_obj;
        struct vm_page *pg;
        int rv, npages;

        pg = NULL;
        npages = 1;

        KASSERT(rw_write_held(uobj->vmobjlock));
        rv = uao_get(&aobj->u_obj, (voff_t)pageidx << PAGE_SHIFT,
            &pg, &npages, 0, PROT_READ | PROT_WRITE, 0, 0);

        /*
         * relock and finish up.
         */
        rw_enter(uobj->vmobjlock, RW_WRITE);
        switch (rv) {
        case VM_PAGER_OK:
                break;

        case VM_PAGER_ERROR:
        case VM_PAGER_REFAULT:
                /*
                 * nothing more to do on errors.
                 * VM_PAGER_REFAULT can only mean that the anon was freed,
                 * so again there's nothing to do.
                 */
                return FALSE;
        }

        /*
         * ok, we've got the page now.
         * mark it as dirty, clear its swslot and un-busy it.
         */
        uao_dropswap(&aobj->u_obj, pageidx);
        atomic_clearbits_int(&pg->pg_flags, PG_BUSY|PG_CLEAN|PG_FAKE);
        UVM_PAGE_OWN(pg, NULL);

        /*
         * deactivate the page (to put it on a page queue).
         */
        uvm_pagedeactivate(pg);

        return FALSE;
}

/*
 * uao_dropswap_range: drop swapslots in the range.
 *
 * => aobj must be locked and is returned locked.
 * => start is inclusive.  end is exclusive.
 */
void
uao_dropswap_range(struct uvm_object *uobj, voff_t start, voff_t end)
{
        struct uvm_aobj *aobj = (struct uvm_aobj *)uobj;
        int swpgonlydelta = 0;

        KASSERT(UVM_OBJ_IS_AOBJ(uobj));
        KASSERT(rw_write_held(uobj->vmobjlock));

        if (end == 0) {
                end = INT64_MAX;
        }

        if (UAO_USES_SWHASH(aobj)) {
                int i, hashbuckets = aobj->u_swhashmask + 1;
                voff_t taghi;
                voff_t taglo;

                taglo = UAO_SWHASH_ELT_TAG(start);
                taghi = UAO_SWHASH_ELT_TAG(end);

                for (i = 0; i < hashbuckets; i++) {
                        struct uao_swhash_elt *elt, *next;

                        for (elt = LIST_FIRST(&aobj->u_swhash[i]);
                             elt != NULL;
                             elt = next) {
                                int startidx, endidx;
                                int j;

                                next = LIST_NEXT(elt, list);

                                if (elt->tag < taglo || taghi < elt->tag) {
                                        continue;
                                }

                                if (elt->tag == taglo) {
                                        startidx =
                                            UAO_SWHASH_ELT_PAGESLOT_IDX(start);
                                } else {
                                        startidx = 0;
                                }

                                if (elt->tag == taghi) {
                                        endidx =
                                            UAO_SWHASH_ELT_PAGESLOT_IDX(end);
                                } else {
                                        endidx = UAO_SWHASH_CLUSTER_SIZE;
                                }

                                for (j = startidx; j < endidx; j++) {
                                        int slot = elt->slots[j];

                                        KASSERT(uvm_pagelookup(&aobj->u_obj,
                                            (voff_t)(UAO_SWHASH_ELT_PAGEIDX_BASE(elt)
                                            + j) << PAGE_SHIFT) == NULL);

                                        if (slot > 0) {
                                                uvm_swap_free(slot, 1);
                                                swpgonlydelta++;
                                                KASSERT(elt->count > 0);
                                                elt->slots[j] = 0;
                                                elt->count--;
                                        }
                                }

                                if (elt->count == 0) {
                                        LIST_REMOVE(elt, list);
                                        pool_put(&uao_swhash_elt_pool, elt);
                                }
                        }
                }
        } else {
                int i;

                if (aobj->u_pages < end) {
                        end = aobj->u_pages;
                }
                for (i = start; i < end; i++) {
                        int slot = aobj->u_swslots[i];

                        if (slot > 0) {
                                uvm_swap_free(slot, 1);
                                swpgonlydelta++;
                        }
                }
        }

        /*
         * adjust the counter of pages only in swap for all
         * the swap slots we've freed.
         */
        if (swpgonlydelta > 0) {
                KASSERT(atomic_load_sint(&uvmexp.swpgonly) >= swpgonlydelta);
                atomic_add_int(&uvmexp.swpgonly, -swpgonlydelta);
        }
}