dhcpcd: update README.DRAGONFLY

[dragonfly.git] / sys / vm / vm_zone.c

/*
 * Copyright (c) 1997, 1998 John S. Dyson.  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 immediately at the beginning of the file, without modification,
 *      this list of conditions, and the following disclaimer.
 * 2. Absolutely no warranty of function or purpose is made by the author
 *      John S. Dyson.
 *
 * $FreeBSD: src/sys/vm/vm_zone.c,v 1.30.2.6 2002/10/10 19:50:16 dillon Exp $
 *
 * Copyright (c) 2003-2017,2019 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Matthew Dillon <dillon@backplane.com>
 *
 * 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. Neither the name of The DragonFly Project nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific, prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/param.h>
#include <sys/queue.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/sysctl.h>
#include <sys/vmmeter.h>

#include <vm/vm.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_map.h>
#include <vm/vm_kern.h>
#include <vm/vm_extern.h>
#include <vm/vm_zone.h>

#include <sys/spinlock2.h>
#include <vm/vm_page2.h>

static MALLOC_DEFINE(M_ZONE, "ZONE", "Zone header");

#define ZONE_ERROR_INVALID 0
#define ZONE_ERROR_NOTFREE 1
#define ZONE_ERROR_ALREADYFREE 2

#define ZONE_ROUNDING   32

#define ZENTRY_FREE     0x12342378

long zone_burst = 128;

static void *zget(vm_zone_t z, int *tryagainp);

/*
 * Return an item from the specified zone.   This function is non-blocking for
 * ZONE_INTERRUPT zones.
 *
 * No requirements.
 */
void *
zalloc(vm_zone_t z)
{
        globaldata_t gd = mycpu;
        vm_zpcpu_t *zpcpu;
        void *item;
        int tryagain;
        long n;

#ifdef INVARIANTS
        if (z == NULL)
                zerror(ZONE_ERROR_INVALID);
#endif
        zpcpu = &z->zpcpu[gd->gd_cpuid];
retry:
        /*
         * Avoid spinlock contention by allocating from a per-cpu queue
         */
        if (zpcpu->zfreecnt > 0) {
                crit_enter_gd(gd);
                if (zpcpu->zfreecnt > 0) {
                        item = zpcpu->zitems;
#ifdef INVARIANTS
                        KASSERT(item != NULL,
                                ("zitems_pcpu unexpectedly NULL"));
                        if (((void **)item)[1] != (void *)ZENTRY_FREE)
                                zerror(ZONE_ERROR_NOTFREE);
                        ((void **)item)[1] = NULL;
#endif
                        zpcpu->zitems = ((void **) item)[0];
                        --zpcpu->zfreecnt;
                        ++zpcpu->znalloc;
                        crit_exit_gd(gd);

                        return item;
                }
                crit_exit_gd(gd);
        }

        /*
         * Per-zone spinlock for the remainder.  Always load at least one
         * item.
         */
        spin_lock(&z->zspin);
        if (z->zfreecnt > z->zfreemin) {
                n = zone_burst;
                do {
                        item = z->zitems;
#ifdef INVARIANTS
                        KASSERT(item != NULL, ("zitems unexpectedly NULL"));
                        if (((void **)item)[1] != (void *)ZENTRY_FREE)
                                zerror(ZONE_ERROR_NOTFREE);
#endif
                        z->zitems = ((void **)item)[0];
                        --z->zfreecnt;
                        ((void **)item)[0] = zpcpu->zitems;
                        zpcpu->zitems = item;
                        ++zpcpu->zfreecnt;
                } while (--n > 0 && z->zfreecnt > z->zfreemin);
                spin_unlock(&z->zspin);
                goto retry;
        } else {
                spin_unlock(&z->zspin);
                tryagain = 0;
                item = zget(z, &tryagain);
                if (tryagain)
                        goto retry;

                /*
                 * PANICFAIL allows the caller to assume that the zalloc()
                 * will always succeed.  If it doesn't, we panic here.
                 */
                if (item == NULL && (z->zflags & ZONE_PANICFAIL))
                        panic("zalloc(%s) failed", z->zname);
        }
        return item;
}

/*
 * Free an item to the specified zone.   
 *
 * No requirements.
 */
void
zfree(vm_zone_t z, void *item)
{
        globaldata_t gd = mycpu;
        vm_zpcpu_t *zpcpu;
        void *tail_item;
        long count;
        long zmax;

        zpcpu = &z->zpcpu[gd->gd_cpuid];

        /*
         * Avoid spinlock contention by freeing into a per-cpu queue
         */
        zmax = z->zmax_pcpu;
        if (zmax < 1024)
                zmax = 1024;

        /*
         * Add to pcpu cache
         */
        crit_enter_gd(gd);
        ((void **)item)[0] = zpcpu->zitems;
#ifdef INVARIANTS
        if (((void **)item)[1] == (void *)ZENTRY_FREE)
                zerror(ZONE_ERROR_ALREADYFREE);
        ((void **)item)[1] = (void *)ZENTRY_FREE;
#endif
        zpcpu->zitems = item;
        ++zpcpu->zfreecnt;

        if (zpcpu->zfreecnt < zmax) {
                crit_exit_gd(gd);
                return;
        }

        /*
         * Hystereis, move (zmax) (calculated below) items to the pool.
         */
        zmax = zmax / 2;
        if (zmax > zone_burst)
                zmax = zone_burst;
        tail_item = item;
        count = 1;

        while (count < zmax) {
                tail_item = ((void **)tail_item)[0];
                ++count;
        }
        zpcpu->zitems = ((void **)tail_item)[0];
        zpcpu->zfreecnt -= count;

        /*
         * Per-zone spinlock for the remainder.
         *
         * Also implement hysteresis by freeing a number of pcpu
         * entries.
         */
        spin_lock(&z->zspin);
        ((void **)tail_item)[0] = z->zitems;
        z->zitems = item;
        z->zfreecnt += count;
        spin_unlock(&z->zspin);

        crit_exit_gd(gd);
}

/*
 * This file comprises a very simple zone allocator.  This is used
 * in lieu of the malloc allocator, where needed or more optimal.
 *
 * Note that the initial implementation of this had coloring, and
 * absolutely no improvement (actually perf degradation) occurred.
 *
 * Note also that the zones are type stable.  The only restriction is
 * that the first two longwords of a data structure can be changed
 * between allocations.  Any data that must be stable between allocations
 * must reside in areas after the first two longwords.
 *
 * zinitna, zinit, zbootinit are the initialization routines.
 * zalloc, zfree, are the allocation/free routines.
 */

LIST_HEAD(zlist, vm_zone) zlist = LIST_HEAD_INITIALIZER(zlist);
static int sysctl_vm_zone(SYSCTL_HANDLER_ARGS);
static vm_pindex_t zone_kmem_pages, zone_kern_pages;
static long zone_kmem_kvaspace;

/*
 * Create a zone, but don't allocate the zone structure.  If the
 * zone had been previously created by the zone boot code, initialize
 * various parts of the zone code.
 *
 * If waits are not allowed during allocation (e.g. during interrupt
 * code), a-priori allocate the kernel virtual space, and allocate
 * only pages when needed.
 *
 * Arguments:
 * z            pointer to zone structure.
 * obj          pointer to VM object (opt).
 * name         name of zone.
 * size         size of zone entries.
 * nentries     number of zone entries allocated (only ZONE_INTERRUPT.)
 * flags        ZONE_INTERRUPT -- items can be allocated at interrupt time.
 * zalloc       number of pages allocated when memory is needed.
 *
 * Note that when using ZONE_INTERRUPT, the size of the zone is limited
 * by the nentries argument.  The size of the memory allocatable is
 * unlimited if ZONE_INTERRUPT is not set.
 *
 * No requirements.
 */
int
zinitna(vm_zone_t z, char *name, size_t size, long nentries, uint32_t flags)
{
        size_t totsize;

        /*
         * Only zones created with zinit() are destroyable.
         */
        if (z->zflags & ZONE_DESTROYABLE)
                panic("zinitna: can't create destroyable zone");

        /*
         * NOTE: We can only adjust zsize if we previously did not
         *       use zbootinit().
         */
        if ((z->zflags & ZONE_BOOT) == 0) {
                z->zsize = roundup2(size, ZONE_ROUNDING);
                spin_init(&z->zspin, "zinitna");
                lockinit(&z->zgetlk, "zgetlk", 0, LK_CANRECURSE);

                z->zfreecnt = 0;
                z->ztotal = 0;
                z->zmax = 0;
                z->zname = name;
                z->zitems = NULL;

                lwkt_gettoken(&vm_token);
                LIST_INSERT_HEAD(&zlist, z, zlink);
                lwkt_reltoken(&vm_token);

                bzero(z->zpcpu, sizeof(z->zpcpu));
        }

        z->zkmvec = NULL;
        z->zkmcur = z->zkmmax = 0;
        z->zflags |= flags;

        /*
         * If we cannot wait, allocate KVA space up front, and we will fill
         * in pages as needed.  This is particularly required when creating
         * an allocation space for map entries in kernel_map, because we
         * do not want to go into a recursion deadlock with 
         * vm_map_entry_reserve().
         */
        if (z->zflags & ZONE_INTERRUPT) {
                totsize = round_page((size_t)z->zsize * nentries);
                atomic_add_long(&zone_kmem_kvaspace, totsize);

                z->zkva = kmem_alloc_pageable(kernel_map, totsize,
                                              VM_SUBSYS_ZALLOC);
                if (z->zkva == 0) {
                        LIST_REMOVE(z, zlink);
                        return 0;
                }

                z->zpagemax = totsize / PAGE_SIZE;
                z->zallocflag = VM_ALLOC_SYSTEM | VM_ALLOC_INTERRUPT |
                                VM_ALLOC_NORMAL | VM_ALLOC_RETRY;
                z->zmax += nentries;

                /*
                 * Set reasonable pcpu cache bounds.  Low-memory systems
                 * might try to cache too little, large-memory systems
                 * might try to cache more than necessarsy.
                 *
                 * In particular, pvzone can wind up being excessive and
                 * waste memory unnecessarily.
                 */
                z->zmax_pcpu = z->zmax / ncpus / 64;
                if (z->zmax_pcpu < 1024)
                        z->zmax_pcpu = 1024;
                if (z->zmax_pcpu * z->zsize > 16*1024*1024)
                        z->zmax_pcpu = 16*1024*1024 / z->zsize;
        } else {
                z->zallocflag = VM_ALLOC_NORMAL | VM_ALLOC_SYSTEM;
                z->zmax = 0;
                z->zmax_pcpu = 8192;
        }


        if (z->zsize > PAGE_SIZE)
                z->zfreemin = 1;
        else
                z->zfreemin = PAGE_SIZE / z->zsize;

        z->zpagecount = 0;

        /*
         * Reduce kernel_map spam by allocating in chunks.
         */
        z->zalloc = ZONE_MAXPGLOAD;

        /*
         * Populate the interrrupt zone at creation time rather than
         * on first allocation, as this is a potentially long operation.
         */
        if (z->zflags & ZONE_INTERRUPT) {
                void *buf;

                buf = zget(z, NULL);
                if (buf)
                        zfree(z, buf);
        }

        return 1;
}

/*
 * Subroutine same as zinitna, except zone data structure is allocated
 * automatically by malloc.  This routine should normally be used, except
 * in certain tricky startup conditions in the VM system -- then
 * zbootinit and zinitna can be used.  Zinit is the standard zone
 * initialization call.
 *
 * No requirements.
 */
vm_zone_t
zinit(char *name, size_t size, long nentries, uint32_t flags)
{
        vm_zone_t z;

        z = (vm_zone_t) kmalloc(sizeof (struct vm_zone), M_ZONE, M_NOWAIT);
        if (z == NULL)
                return NULL;

        z->zflags = 0;
        if (zinitna(z, name, size, nentries, flags & ~ZONE_DESTROYABLE) == 0) {
                kfree(z, M_ZONE);
                return NULL;
        }

        if (flags & ZONE_DESTROYABLE)
                z->zflags |= ZONE_DESTROYABLE;

        return z;
}

/*
 * Initialize a zone before the system is fully up.  This routine should
 * only be called before full VM startup.
 *
 * Called from the low level boot code only.
 */
void
zbootinit(vm_zone_t z, char *name, size_t size, void *item, long nitems)
{
        long i;

        spin_init(&z->zspin, "zbootinit");
        lockinit(&z->zgetlk, "zgetlk", 0, LK_CANRECURSE);
        bzero(z->zpcpu, sizeof(z->zpcpu));
        z->zname = name;
        z->zsize = size;
        z->zpagemax = 0;
        z->zflags = ZONE_BOOT;
        z->zfreemin = 0;
        z->zallocflag = 0;
        z->zpagecount = 0;
        z->zalloc = 0;

        bzero(item, (size_t)nitems * z->zsize);
        z->zitems = NULL;
        for (i = 0; i < nitems; i++) {
                ((void **)item)[0] = z->zitems;
#ifdef INVARIANTS
                ((void **)item)[1] = (void *)ZENTRY_FREE;
#endif
                z->zitems = item;
                item = (uint8_t *)item + z->zsize;
        }
        z->zfreecnt = nitems;
        z->zmax = nitems;
        z->ztotal = nitems;

        lwkt_gettoken(&vm_token);
        LIST_INSERT_HEAD(&zlist, z, zlink);
        lwkt_reltoken(&vm_token);
}

/*
 * Release all resources owned by zone created with zinit().
 *
 * No requirements.
 */
void
zdestroy(vm_zone_t z)
{
        vm_pindex_t i;

        if (z == NULL)
                panic("zdestroy: null zone");
        if ((z->zflags & ZONE_DESTROYABLE) == 0)
                panic("zdestroy: undestroyable zone");

        lwkt_gettoken(&vm_token);
        LIST_REMOVE(z, zlink);
        lwkt_reltoken(&vm_token);

        /*
         * Release virtual mappings, physical memory and update sysctl stats.
         */
        KKASSERT((z->zflags & ZONE_INTERRUPT) == 0);
        for (i = 0; i < z->zkmcur; i++) {
                kmem_free(kernel_map, z->zkmvec[i],
                          (size_t)z->zalloc * PAGE_SIZE);
                atomic_subtract_long(&zone_kern_pages, z->zalloc);
        }
        if (z->zkmvec != NULL)
                kfree(z->zkmvec, M_ZONE);

        spin_uninit(&z->zspin);
        kfree(z, M_ZONE);
}


/*
 * void *zalloc(vm_zone_t zone) --
 *      Returns an item from a specified zone.  May not be called from a
 *      FAST interrupt or IPI function.
 *
 * void zfree(vm_zone_t zone, void *item) --
 *      Frees an item back to a specified zone.  May not be called from a
 *      FAST interrupt or IPI function.
 */

/*
 * Internal zone routine.  Not to be called from external (non vm_zone) code.
 *
 * This function may return NULL.
 *
 * No requirements.
 */
static void *
zget(vm_zone_t z, int *tryagainp)
{
        vm_page_t pgs[ZONE_MAXPGLOAD];
        vm_page_t m;
        long nitems;
        long savezpc;
        size_t nbytes;
        size_t noffset;
        void *item;
        vm_pindex_t npages;
        vm_pindex_t nalloc;
        vm_pindex_t i;

        if (z == NULL)
                panic("zget: null zone");

        /*
         * We need an encompassing per-zone lock for zget() refills.
         *
         * Without this we wind up locking on the vm_map inside kmem_alloc*()
         * prior to any entries actually being added to the zone, potentially
         * exhausting the per-cpu cache of vm_map_entry's when multiple threads
         * are blocked on the same lock on the same cpu.
         */
        if ((z->zflags & ZONE_INTERRUPT) == 0) {
                if (lockmgr(&z->zgetlk, LK_EXCLUSIVE | LK_SLEEPFAIL)) {
                        *tryagainp = 1;
                        return NULL;
                }
        }

        if (z->zflags & ZONE_INTERRUPT) {
                /*
                 * Interrupt zones do not mess with the kernel_map, they
                 * simply populate an existing mapping.
                 *
                 * First allocate as many pages as we can, stopping at
                 * our limit or if the page allocation fails.  Try to
                 * avoid exhausting the interrupt free minimum by backing
                 * off to normal page allocations after a certain point.
                 */
                for (i = 0; i < ZONE_MAXPGLOAD && i < z->zalloc; ++i) {
                        if (i < 4) {
                                m = vm_page_alloc(NULL,
                                                  mycpu->gd_rand_incr++,
                                                  z->zallocflag);
                        } else {
                                m = vm_page_alloc(NULL,
                                                  mycpu->gd_rand_incr++,
                                                  VM_ALLOC_NORMAL |
                                                  VM_ALLOC_SYSTEM);
                        }
                        if (m == NULL)
                                break;
                        pgs[i] = m;
                }
                nalloc = i;

                /*
                 * Account for the pages.
                 *
                 * NOTE! Do not allow overlap with a prior page as it
                 *       may still be undergoing allocation on another
                 *       cpu.
                 */
                spin_lock(&z->zspin);
                noffset = (size_t)z->zpagecount * PAGE_SIZE;
                /* noffset -= noffset % z->zsize; */
                savezpc = z->zpagecount;

                /*
                 * Track total memory use and kmem offset.
                 */
                if (z->zpagecount + nalloc > z->zpagemax)
                        z->zpagecount = z->zpagemax;
                else
                        z->zpagecount += nalloc;

                item = (char *)z->zkva + noffset;
                npages = z->zpagecount - savezpc;
                nitems = ((size_t)(savezpc + npages) * PAGE_SIZE - noffset) /
                         z->zsize;
                atomic_add_long(&zone_kmem_pages, npages);
                spin_unlock(&z->zspin);

                /*
                 * Enter the pages into the reserved KVA space.
                 */
                for (i = 0; i < npages; ++i) {
                        vm_offset_t zkva;

                        m = pgs[i];
                        KKASSERT(m->queue == PQ_NONE);
                        m->valid = VM_PAGE_BITS_ALL;
                        vm_page_wire(m);
                        vm_page_wakeup(m);

                        zkva = z->zkva + (size_t)(savezpc + i) * PAGE_SIZE;
                        pmap_kenter(zkva, VM_PAGE_TO_PHYS(m));
                        bzero((void *)zkva, PAGE_SIZE);
                }
                for (i = npages; i < nalloc; ++i) {
                        m = pgs[i];
                        vm_page_free(m);
                }
        } else if (z->zflags & ZONE_SPECIAL) {
                /*
                 * The special zone is the one used for vm_map_entry_t's.
                 * We have to avoid an infinite recursion in 
                 * vm_map_entry_reserve() by using vm_map_entry_kreserve()
                 * instead.  The map entries are pre-reserved by the kernel
                 * by vm_map_entry_reserve_cpu_init().
                 */
                nbytes = (size_t)z->zalloc * PAGE_SIZE;
                z->zpagecount += z->zalloc;     /* Track total memory use */

                item = (void *)kmem_alloc3(kernel_map, nbytes,
                                           VM_SUBSYS_ZALLOC, KM_KRESERVE);

                /* note: z might be modified due to blocking */
                if (item != NULL) {
                        atomic_add_long(&zone_kern_pages, z->zalloc);
                        bzero(item, nbytes);
                } else {
                        nbytes = 0;
                }
                nitems = nbytes / z->zsize;
        } else {
                /*
                 * Otherwise allocate KVA from the kernel_map.
                 */
                nbytes = (size_t)z->zalloc * PAGE_SIZE;
                z->zpagecount += z->zalloc;     /* Track total memory use */

                item = (void *)kmem_alloc3(kernel_map, nbytes,
                                           VM_SUBSYS_ZALLOC, 0);

                /* note: z might be modified due to blocking */
                if (item != NULL) {
                        atomic_add_long(&zone_kern_pages, z->zalloc);
                        bzero(item, nbytes);

                        if (z->zflags & ZONE_DESTROYABLE) {
                                if (z->zkmcur == z->zkmmax) {
                                        z->zkmmax =
                                                z->zkmmax==0 ? 1 : z->zkmmax*2;
                                        z->zkmvec = krealloc(z->zkmvec,
                                            z->zkmmax * sizeof(z->zkmvec[0]),
                                            M_ZONE, M_WAITOK);
                                }
                                z->zkmvec[z->zkmcur++] = (vm_offset_t)item;
                        }
                } else {
                        nbytes = 0;
                }
                nitems = nbytes / z->zsize;
        }

        /*
         * Enter any new pages into the pool, reserving one, or get the
         * item from the existing pool.
         */
        spin_lock(&z->zspin);
        z->ztotal += nitems;

        /*
         * The zone code may need to allocate kernel memory, which can
         * recurse zget() infinitely if we do not handle it properly.
         * We deal with this by directly repopulating the pcpu vm_map_entry
         * cache.
         */
        if (nitems > 1 && (z->zflags & ZONE_SPECIAL)) {
                struct globaldata *gd = mycpu;
                vm_map_entry_t entry;

                /*
                 * Make sure we have enough structures in gd_vme_base to handle
                 * the reservation request.
                 *
                 * The critical section protects access to the per-cpu gd.
                 */
                crit_enter();
                while (gd->gd_vme_avail < 2 && nitems > 1) {
                        entry = item;
                        MAPENT_FREELIST(entry) = gd->gd_vme_base;
                        gd->gd_vme_base = entry;
                        atomic_add_int(&gd->gd_vme_avail, 1);
                        item = (uint8_t *)item + z->zsize;
                        --nitems;
                }
                crit_exit();
        }

        if (nitems != 0) {
                /*
                 * Enter pages into the pool saving one for immediate
                 * allocation.
                 */
                nitems -= 1;
                for (i = 0; i < nitems; i++) {
                        ((void **)item)[0] = z->zitems;
#ifdef INVARIANTS
                        ((void **)item)[1] = (void *)ZENTRY_FREE;
#endif
                        z->zitems = item;
                        item = (uint8_t *)item + z->zsize;
                }
                z->zfreecnt += nitems;
                ++z->znalloc;
        } else if (z->zfreecnt > 0) {
                /*
                 * Get an item from the existing pool.
                 */
                item = z->zitems;
                z->zitems = ((void **)item)[0];
#ifdef INVARIANTS
                if (((void **)item)[1] != (void *)ZENTRY_FREE)
                        zerror(ZONE_ERROR_NOTFREE);
                ((void **) item)[1] = NULL;
#endif
                --z->zfreecnt;
                ++z->znalloc;
        } else {
                /*
                 * No items available.
                 */
                item = NULL;
        }
        spin_unlock(&z->zspin);

        /*
         * Release the per-zone global lock after the items have been
         * added.  Any other threads blocked in zget()'s zgetlk will
         * then retry rather than potentially exhaust the per-cpu cache
         * of vm_map_entry structures doing their own kmem_alloc() calls,
         * or allocating excessive amounts of space unnecessarily.
         */
        if ((z->zflags & ZONE_INTERRUPT) == 0)
                lockmgr(&z->zgetlk, LK_RELEASE);

        return item;
}

/*
 * No requirements.
 */
static int
sysctl_vm_zone(SYSCTL_HANDLER_ARGS)
{
        vm_zone_t curzone;
        char tmpbuf[128];
        char tmpname[14];
        int error = 0;

        ksnprintf(tmpbuf, sizeof(tmpbuf),
            "\nITEM            SIZE     LIMIT    USED    FREE  REQUESTS\n");
        error = SYSCTL_OUT(req, tmpbuf, strlen(tmpbuf));
        if (error)
                return (error);

        lwkt_gettoken(&vm_token);
        LIST_FOREACH(curzone, &zlist, zlink) {
                size_t i;
                size_t len;
                int offset;
                long freecnt;
                long znalloc;
                int n;

                len = strlen(curzone->zname);
                if (len >= (sizeof(tmpname) - 1))
                        len = (sizeof(tmpname) - 1);
                for(i = 0; i < sizeof(tmpname) - 1; i++)
                        tmpname[i] = ' ';
                tmpname[i] = 0;
                memcpy(tmpname, curzone->zname, len);
                tmpname[len] = ':';
                offset = 0;
                if (curzone == LIST_FIRST(&zlist)) {
                        offset = 1;
                        tmpbuf[0] = '\n';
                }
                freecnt = curzone->zfreecnt;
                znalloc = curzone->znalloc;
                for (n = 0; n < ncpus; ++n) {
                        freecnt += curzone->zpcpu[n].zfreecnt;
                        znalloc += curzone->zpcpu[n].znalloc;
                }

                ksnprintf(tmpbuf + offset, sizeof(tmpbuf) - offset,
                        "%s %6.6lu, %8.8lu, %6.6lu, %6.6lu, %8.8lu\n",
                        tmpname, curzone->zsize, curzone->zmax,
                        (curzone->ztotal - freecnt),
                        freecnt, znalloc);

                len = strlen((char *)tmpbuf);
                if (LIST_NEXT(curzone, zlink) == NULL)
                        tmpbuf[len - 1] = 0;

                error = SYSCTL_OUT(req, tmpbuf, len);

                if (error)
                        break;
        }
        lwkt_reltoken(&vm_token);
        return (error);
}

#if defined(INVARIANTS)

/*
 * Debugging only.
 */
void
zerror(int error)
{
        char *msg;

        switch (error) {
        case ZONE_ERROR_INVALID:
                msg = "zone: invalid zone";
                break;
        case ZONE_ERROR_NOTFREE:
                msg = "zone: entry not free";
                break;
        case ZONE_ERROR_ALREADYFREE:
                msg = "zone: freeing free entry";
                break;
        default:
                msg = "zone: invalid error";
                break;
        }
        panic("%s", msg);
}
#endif

SYSCTL_OID(_vm, OID_AUTO, zone, CTLTYPE_STRING|CTLFLAG_RD, \
        NULL, 0, sysctl_vm_zone, "A", "Zone Info");

SYSCTL_LONG(_vm, OID_AUTO, zone_kmem_pages,
        CTLFLAG_RD, &zone_kmem_pages, 0, "Number of interrupt safe pages allocated by zone");
SYSCTL_LONG(_vm, OID_AUTO, zone_burst,
        CTLFLAG_RW, &zone_burst, 0, "Burst from depot to pcpu cache");
SYSCTL_LONG(_vm, OID_AUTO, zone_kmem_kvaspace,
        CTLFLAG_RD, &zone_kmem_kvaspace, 0, "KVA space allocated by zone");
SYSCTL_LONG(_vm, OID_AUTO, zone_kern_pages,
        CTLFLAG_RD, &zone_kern_pages, 0, "Number of non-interrupt safe pages allocated by zone");