vm_swapout.c

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/*-
 * SPDX-License-Identifier: (BSD-4-Clause AND MIT-CMU)
 *
 * Copyright (c) 1991 Regents of the University of California.
 * All rights reserved.
 * Copyright (c) 1994 John S. Dyson
 * All rights reserved.
 * Copyright (c) 1994 David Greenman
 * All rights reserved.
 * Copyright (c) 2005 Yahoo! Technologies Norway AS
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * The Mach Operating System project at Carnegie-Mellon University.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      from: @(#)vm_pageout.c  7.4 (Berkeley) 5/7/91
 *
 *
 * Copyright (c) 1987, 1990 Carnegie-Mellon University.
 * All rights reserved.
 *
 * Authors: Avadis Tevanian, Jr., Michael Wayne Young
 *
 * Permission to use, copy, modify and distribute this software and
 * its documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 *
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
 * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 *
 * Carnegie Mellon requests users of this software to return to
 *
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 *
 * any improvements or extensions that they make and grant Carnegie the
 * rights to redistribute these changes.
 */
 
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
 
#include "opt_kstack_pages.h"
#include "opt_kstack_max_pages.h"
#include "opt_vm.h"
 
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/limits.h>
#include <sys/kernel.h>
#include <sys/eventhandler.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/kthread.h>
#include <sys/ktr.h>
#include <sys/mount.h>
#include <sys/racct.h>
#include <sys/resourcevar.h>
#include <sys/refcount.h>
#include <sys/sched.h>
#include <sys/sdt.h>
#include <sys/signalvar.h>
#include <sys/smp.h>
#include <sys/time.h>
#include <sys/vnode.h>
#include <sys/vmmeter.h>
#include <sys/rwlock.h>
#include <sys/sx.h>
#include <sys/sysctl.h>
 
#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/vm_kern.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_map.h>
#include <vm/vm_pageout.h>
#include <vm/vm_pager.h>
#include <vm/vm_phys.h>
#include <vm/swap_pager.h>
#include <vm/vm_extern.h>
#include <vm/uma.h>
 
/* the kernel process "vm_daemon" */
static void vm_daemon(void);
static struct proc *vmproc;
 
static struct kproc_desc vm_kp = {
        "vmdaemon",
        vm_daemon,
        &vmproc
};
SYSINIT(vmdaemon, SI_SUB_KTHREAD_VM, SI_ORDER_FIRST, kproc_start, &vm_kp);
 
static int vm_swap_enabled = 1;
static int vm_swap_idle_enabled = 0;
 
SYSCTL_INT(_vm, VM_SWAPPING_ENABLED, swap_enabled, CTLFLAG_RW,
    &vm_swap_enabled, 0,
    "Enable entire process swapout");
SYSCTL_INT(_vm, OID_AUTO, swap_idle_enabled, CTLFLAG_RW,
    &vm_swap_idle_enabled, 0,
    "Allow swapout on idle criteria");
 
/*
 * Swap_idle_threshold1 is the guaranteed swapped in time for a process
 */
static int swap_idle_threshold1 = 2;
SYSCTL_INT(_vm, OID_AUTO, swap_idle_threshold1, CTLFLAG_RW,
    &swap_idle_threshold1, 0,
    "Guaranteed swapped in time for a process");
 
/*
 * Swap_idle_threshold2 is the time that a process can be idle before
 * it will be swapped out, if idle swapping is enabled.
 */
static int swap_idle_threshold2 = 10;
SYSCTL_INT(_vm, OID_AUTO, swap_idle_threshold2, CTLFLAG_RW,
    &swap_idle_threshold2, 0,
    "Time before a process will be swapped out");
 
static int vm_daemon_timeout = 0;
SYSCTL_INT(_vm, OID_AUTO, vmdaemon_timeout, CTLFLAG_RW,
    &vm_daemon_timeout, 0,
    "Time between vmdaemon runs");
 
static int vm_pageout_req_swapout;      /* XXX */
static int vm_daemon_needed;
static struct mtx vm_daemon_mtx;
/* Allow for use by vm_pageout before vm_daemon is initialized. */
MTX_SYSINIT(vm_daemon, &vm_daemon_mtx, "vm daemon", MTX_DEF);
 
static int swapped_cnt;
static int swap_inprogress;     /* Pending swap-ins done outside swapper. */
static int last_swapin;
 
static void swapclear(struct proc *);
static int swapout(struct proc *);
static void vm_swapout_map_deactivate_pages(vm_map_t, long);
static void vm_swapout_object_deactivate(pmap_t, vm_object_t, long);
static void swapout_procs(int action);
static void vm_req_vmdaemon(int req);
static void vm_thread_swapout(struct thread *td);
 
static void
vm_swapout_object_deactivate_page(pmap_t pmap, vm_page_t m, bool unmap)
{
 
        /*
         * Ignore unreclaimable wired pages.  Repeat the check after busying
         * since a busy holder may wire the page.
         */
        if (vm_page_wired(m) || !vm_page_tryxbusy(m))
                return;
 
        if (vm_page_wired(m) || !pmap_page_exists_quick(pmap, m)) {
                vm_page_xunbusy(m);
                return;
        }
        if (!pmap_is_referenced(m)) {
                if (!vm_page_active(m))
                        (void)vm_page_try_remove_all(m);
                else if (unmap && vm_page_try_remove_all(m))
                        vm_page_deactivate(m);
        }
        vm_page_xunbusy(m);
}
 
/*
 *      vm_swapout_object_deactivate
 *
 *      Deactivate enough pages to satisfy the inactive target
 *      requirements.
 *
 *      The object and map must be locked.
 */
static void
vm_swapout_object_deactivate(pmap_t pmap, vm_object_t first_object,
    long desired)
{
        vm_object_t backing_object, object;
        vm_page_t m;
        bool unmap;
 
        VM_OBJECT_ASSERT_LOCKED(first_object);
        if ((first_object->flags & OBJ_FICTITIOUS) != 0)
                return;
        for (object = first_object;; object = backing_object) {
                if (pmap_resident_count(pmap) <= desired)
                        goto unlock_return;
                VM_OBJECT_ASSERT_LOCKED(object);
                if ((object->flags & OBJ_UNMANAGED) != 0 ||
                    blockcount_read(&object->paging_in_progress) > 0)
                        goto unlock_return;
 
                unmap = true;
                if (object->shadow_count > 1)
                        unmap = false;
 
                /*
                 * Scan the object's entire memory queue.
                 */
                TAILQ_FOREACH(m, &object->memq, listq) {
                        if (pmap_resident_count(pmap) <= desired)
                                goto unlock_return;
                        if (should_yield())
                                goto unlock_return;
                        vm_swapout_object_deactivate_page(pmap, m, unmap);
                }
                if ((backing_object = object->backing_object) == NULL)
                        goto unlock_return;
                VM_OBJECT_RLOCK(backing_object);
                if (object != first_object)
                        VM_OBJECT_RUNLOCK(object);
        }
unlock_return:
        if (object != first_object)
                VM_OBJECT_RUNLOCK(object);
}
 
/*
 * deactivate some number of pages in a map, try to do it fairly, but
 * that is really hard to do.
 */
static void
vm_swapout_map_deactivate_pages(vm_map_t map, long desired)
{
        vm_map_entry_t tmpe;
        vm_object_t obj, bigobj;
        int nothingwired;
 
        if (!vm_map_trylock_read(map))
                return;
 
        bigobj = NULL;
        nothingwired = TRUE;
 
        /*
         * first, search out the biggest object, and try to free pages from
         * that.
         */
        VM_MAP_ENTRY_FOREACH(tmpe, map) {
                if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
                        obj = tmpe->object.vm_object;
                        if (obj != NULL && VM_OBJECT_TRYRLOCK(obj)) {
                                if (obj->shadow_count <= 1 &&
                                    (bigobj == NULL ||
                                     bigobj->resident_page_count <
                                     obj->resident_page_count)) {
                                        if (bigobj != NULL)
                                                VM_OBJECT_RUNLOCK(bigobj);
                                        bigobj = obj;
                                } else
                                        VM_OBJECT_RUNLOCK(obj);
                        }
                }
                if (tmpe->wired_count > 0)
                        nothingwired = FALSE;
        }
 
        if (bigobj != NULL) {
                vm_swapout_object_deactivate(map->pmap, bigobj, desired);
                VM_OBJECT_RUNLOCK(bigobj);
        }
        /*
         * Next, hunt around for other pages to deactivate.  We actually
         * do this search sort of wrong -- .text first is not the best idea.
         */
        VM_MAP_ENTRY_FOREACH(tmpe, map) {
                if (pmap_resident_count(vm_map_pmap(map)) <= desired)
                        break;
                if ((tmpe->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
                        obj = tmpe->object.vm_object;
                        if (obj != NULL) {
                                VM_OBJECT_RLOCK(obj);
                                vm_swapout_object_deactivate(map->pmap, obj,
                                    desired);
                                VM_OBJECT_RUNLOCK(obj);
                        }
                }
        }
 
        /*
         * Remove all mappings if a process is swapped out, this will free page
         * table pages.
         */
        if (desired == 0 && nothingwired) {
                pmap_remove(vm_map_pmap(map), vm_map_min(map),
                    vm_map_max(map));
        }
 
        vm_map_unlock_read(map);
}
 
/*
 * Swap out requests
 */
#define VM_SWAP_NORMAL 1
#define VM_SWAP_IDLE 2
 
void
vm_swapout_run(void)
{
 
        if (vm_swap_enabled)
                vm_req_vmdaemon(VM_SWAP_NORMAL);
}
 
/*
 * Idle process swapout -- run once per second when pagedaemons are
 * reclaiming pages.
 */
void
vm_swapout_run_idle(void)
{
        static long lsec;
 
        if (!vm_swap_idle_enabled || time_second == lsec)
                return;
        vm_req_vmdaemon(VM_SWAP_IDLE);
        lsec = time_second;
}
 
static void
vm_req_vmdaemon(int req)
{
        static int lastrun = 0;
 
        mtx_lock(&vm_daemon_mtx);
        vm_pageout_req_swapout |= req;
        if ((ticks > (lastrun + hz)) || (ticks < lastrun)) {
                wakeup(&vm_daemon_needed);
                lastrun = ticks;
        }
        mtx_unlock(&vm_daemon_mtx);
}
 
static void
vm_daemon(void)
{
        struct rlimit rsslim;
        struct proc *p;
        struct thread *td;
        struct vmspace *vm;
        int breakout, swapout_flags, tryagain, attempts;
#ifdef RACCT
        uint64_t rsize, ravailable;
 
        if (racct_enable && vm_daemon_timeout == 0)
                vm_daemon_timeout = hz;
#endif
 
        while (TRUE) {
                mtx_lock(&vm_daemon_mtx);
                msleep(&vm_daemon_needed, &vm_daemon_mtx, PPAUSE, "psleep",
                    vm_daemon_timeout);
                swapout_flags = vm_pageout_req_swapout;
                vm_pageout_req_swapout = 0;
                mtx_unlock(&vm_daemon_mtx);
                if (swapout_flags != 0) {
                        /*
                         * Drain the per-CPU page queue batches as a deadlock
                         * avoidance measure.
                         */
                        if ((swapout_flags & VM_SWAP_NORMAL) != 0)
                                vm_page_pqbatch_drain();
                        swapout_procs(swapout_flags);
                }
 
                /*
                 * scan the processes for exceeding their rlimits or if
                 * process is swapped out -- deactivate pages
                 */
                tryagain = 0;
                attempts = 0;
again:
                attempts++;
                sx_slock(&allproc_lock);
                FOREACH_PROC_IN_SYSTEM(p) {
                        vm_pindex_t limit, size;
 
                        /*
                         * if this is a system process or if we have already
                         * looked at this process, skip it.
                         */
                        PROC_LOCK(p);
                        if (p->p_state != PRS_NORMAL ||
                            p->p_flag & (P_INEXEC | P_SYSTEM | P_WEXIT)) {
                                PROC_UNLOCK(p);
                                continue;
                        }
                        /*
                         * if the process is in a non-running type state,
                         * don't touch it.
                         */
                        breakout = 0;
                        FOREACH_THREAD_IN_PROC(p, td) {
                                thread_lock(td);
                                if (!TD_ON_RUNQ(td) &&
                                    !TD_IS_RUNNING(td) &&
                                    !TD_IS_SLEEPING(td) &&
                                    !TD_IS_SUSPENDED(td)) {
                                        thread_unlock(td);
                                        breakout = 1;
                                        break;
                                }
                                thread_unlock(td);
                        }
                        if (breakout) {
                                PROC_UNLOCK(p);
                                continue;
                        }
                        /*
                         * get a limit
                         */
                        lim_rlimit_proc(p, RLIMIT_RSS, &rsslim);
                        limit = OFF_TO_IDX(
                            qmin(rsslim.rlim_cur, rsslim.rlim_max));
 
                        /*
                         * let processes that are swapped out really be
                         * swapped out set the limit to nothing (will force a
                         * swap-out.)
                         */
                        if ((p->p_flag & P_INMEM) == 0)
                                limit = 0;      /* XXX */
                        vm = vmspace_acquire_ref(p);
                        _PHOLD_LITE(p);
                        PROC_UNLOCK(p);
                        if (vm == NULL) {
                                PRELE(p);
                                continue;
                        }
                        sx_sunlock(&allproc_lock);
 
                        size = vmspace_resident_count(vm);
                        if (size >= limit) {
                                vm_swapout_map_deactivate_pages(
                                    &vm->vm_map, limit);
                                size = vmspace_resident_count(vm);
                        }
#ifdef RACCT
                        if (racct_enable) {
                                rsize = IDX_TO_OFF(size);
                                PROC_LOCK(p);
                                if (p->p_state == PRS_NORMAL)
                                        racct_set(p, RACCT_RSS, rsize);
                                ravailable = racct_get_available(p, RACCT_RSS);
                                PROC_UNLOCK(p);
                                if (rsize > ravailable) {
                                        /*
                                         * Don't be overly aggressive; this
                                         * might be an innocent process,
                                         * and the limit could've been exceeded
                                         * by some memory hog.  Don't try
                                         * to deactivate more than 1/4th
                                         * of process' resident set size.
                                         */
                                        if (attempts <= 8) {
                                                if (ravailable < rsize -
                                                    (rsize / 4)) {
                                                        ravailable = rsize -
                                                            (rsize / 4);
                                                }
                                        }
                                        vm_swapout_map_deactivate_pages(
                                            &vm->vm_map,
                                            OFF_TO_IDX(ravailable));
                                        /* Update RSS usage after paging out. */
                                        size = vmspace_resident_count(vm);
                                        rsize = IDX_TO_OFF(size);
                                        PROC_LOCK(p);
                                        if (p->p_state == PRS_NORMAL)
                                                racct_set(p, RACCT_RSS, rsize);
                                        PROC_UNLOCK(p);
                                        if (rsize > ravailable)
                                                tryagain = 1;
                                }
                        }
#endif
                        vmspace_free(vm);
                        sx_slock(&allproc_lock);
                        PRELE(p);
                }
                sx_sunlock(&allproc_lock);
                if (tryagain != 0 && attempts <= 10) {
                        maybe_yield();
                        goto again;
                }
        }
}
 
/*
 * Allow a thread's kernel stack to be paged out.
 */
static void
vm_thread_swapout(struct thread *td)
{
        vm_page_t m;
        vm_offset_t kaddr;
        vm_pindex_t pindex;
        int i, pages;
 
        cpu_thread_swapout(td);
        kaddr = td->td_kstack;
        pages = td->td_kstack_pages;
        pindex = atop(kaddr - VM_MIN_KERNEL_ADDRESS);
        pmap_qremove(kaddr, pages);
        VM_OBJECT_WLOCK(kstack_object);
        for (i = 0; i < pages; i++) {
                m = vm_page_lookup(kstack_object, pindex + i);
                if (m == NULL)
                        panic("vm_thread_swapout: kstack already missing?");
                vm_page_dirty(m);
                vm_page_xunbusy_unchecked(m);
                vm_page_unwire(m, PQ_LAUNDRY);
        }
        VM_OBJECT_WUNLOCK(kstack_object);
}
 
/*
 * Bring the kernel stack for a specified thread back in.
 */
static void
vm_thread_swapin(struct thread *td, int oom_alloc)
{
        vm_page_t ma[KSTACK_MAX_PAGES];
        vm_offset_t kaddr;
        int a, count, i, j, pages, rv;
 
        kaddr = td->td_kstack;
        pages = td->td_kstack_pages;
        vm_thread_stack_back(td->td_domain.dr_policy, kaddr, ma, pages,
            oom_alloc);
        for (i = 0; i < pages;) {
                vm_page_assert_xbusied(ma[i]);
                if (vm_page_all_valid(ma[i])) {
                        i++;
                        continue;
                }
                vm_object_pip_add(kstack_object, 1);
                for (j = i + 1; j < pages; j++)
                        if (vm_page_all_valid(ma[j]))
                                break;
                VM_OBJECT_WLOCK(kstack_object);
                rv = vm_pager_has_page(kstack_object, ma[i]->pindex, NULL, &a);
                VM_OBJECT_WUNLOCK(kstack_object);
                KASSERT(rv == 1, ("%s: missing page %p", __func__, ma[i]));
                count = min(a + 1, j - i);
                rv = vm_pager_get_pages(kstack_object, ma + i, count, NULL, NULL);
                KASSERT(rv == VM_PAGER_OK, ("%s: cannot get kstack for proc %d",
                    __func__, td->td_proc->p_pid));
                vm_object_pip_wakeup(kstack_object);
                i += count;
        }
        pmap_qenter(kaddr, ma, pages);
        cpu_thread_swapin(td);
}
 
void
faultin(struct proc *p)
{
        struct thread *td;
        int oom_alloc;
 
        PROC_LOCK_ASSERT(p, MA_OWNED);
 
        /*
         * If another process is swapping in this process,
         * just wait until it finishes.
         */
        if (p->p_flag & P_SWAPPINGIN) {
                while (p->p_flag & P_SWAPPINGIN)
                        msleep(&p->p_flag, &p->p_mtx, PVM, "faultin", 0);
                return;
        }
 
        if ((p->p_flag & P_INMEM) == 0) {
                oom_alloc = (p->p_flag & P_WKILLED) != 0 ? VM_ALLOC_SYSTEM :
                    VM_ALLOC_NORMAL;
 
                /*
                 * Don't let another thread swap process p out while we are
                 * busy swapping it in.
                 */
                ++p->p_lock;
                p->p_flag |= P_SWAPPINGIN;
                PROC_UNLOCK(p);
                sx_xlock(&allproc_lock);
                MPASS(swapped_cnt > 0);
                swapped_cnt--;
                if (curthread != &thread0)
                        swap_inprogress++;
                sx_xunlock(&allproc_lock);
 
                /*
                 * We hold no lock here because the list of threads
                 * can not change while all threads in the process are
                 * swapped out.
                 */
                FOREACH_THREAD_IN_PROC(p, td)
                        vm_thread_swapin(td, oom_alloc);
 
                if (curthread != &thread0) {
                        sx_xlock(&allproc_lock);
                        MPASS(swap_inprogress > 0);
                        swap_inprogress--;
                        last_swapin = ticks;
                        sx_xunlock(&allproc_lock);
                }
                PROC_LOCK(p);
                swapclear(p);
                p->p_swtick = ticks;
 
                /* Allow other threads to swap p out now. */
                wakeup(&p->p_flag);
                --p->p_lock;
        }
}
 
/*
 * This swapin algorithm attempts to swap-in processes only if there
 * is enough space for them.  Of course, if a process waits for a long
 * time, it will be swapped in anyway.
 */
 
static struct proc *
swapper_selector(bool wkilled_only)
{
        struct proc *p, *res;
        struct thread *td;
        int ppri, pri, slptime, swtime;
 
        sx_assert(&allproc_lock, SA_SLOCKED);
        if (swapped_cnt == 0)
                return (NULL);
        res = NULL;
        ppri = INT_MIN;
        FOREACH_PROC_IN_SYSTEM(p) {
                PROC_LOCK(p);
                if (p->p_state == PRS_NEW || (p->p_flag & (P_SWAPPINGOUT |
                    P_SWAPPINGIN | P_INMEM)) != 0) {
                        PROC_UNLOCK(p);
                        continue;
                }
                if (p->p_state == PRS_NORMAL && (p->p_flag & P_WKILLED) != 0) {
                        /*
                         * A swapped-out process might have mapped a
                         * large portion of the system's pages as
                         * anonymous memory.  There is no other way to
                         * release the memory other than to kill the
                         * process, for which we need to swap it in.
                         */
                        return (p);
                }
                if (wkilled_only) {
                        PROC_UNLOCK(p);
                        continue;
                }
                swtime = (ticks - p->p_swtick) / hz;
                FOREACH_THREAD_IN_PROC(p, td) {
                        /*
                         * An otherwise runnable thread of a process
                         * swapped out has only the TDI_SWAPPED bit set.
                         */
                        thread_lock(td);
                        if (td->td_inhibitors == TDI_SWAPPED) {
                                slptime = (ticks - td->td_slptick) / hz;
                                pri = swtime + slptime;
                                if ((td->td_flags & TDF_SWAPINREQ) == 0)
                                        pri -= p->p_nice * 8;
                                /*
                                 * if this thread is higher priority
                                 * and there is enough space, then select
                                 * this process instead of the previous
                                 * selection.
                                 */
                                if (pri > ppri) {
                                        res = p;
                                        ppri = pri;
                                }
                        }
                        thread_unlock(td);
                }
                PROC_UNLOCK(p);
        }
 
        if (res != NULL)
                PROC_LOCK(res);
        return (res);
}
 
#define SWAPIN_INTERVAL (MAXSLP * hz / 2)
 
/*
 * Limit swapper to swap in one non-WKILLED process in MAXSLP/2
 * interval, assuming that there is:
 * - at least one domain that is not suffering from a shortage of free memory;
 * - no parallel swap-ins;
 * - no other swap-ins in the current SWAPIN_INTERVAL.
 */
static bool
swapper_wkilled_only(void)
{
 
        return (vm_page_count_min_set(&all_domains) || swap_inprogress > 0 ||
            (u_int)(ticks - last_swapin) < SWAPIN_INTERVAL);
}
 
void
swapper(void)
{
        struct proc *p;
 
        for (;;) {
                sx_slock(&allproc_lock);
                p = swapper_selector(swapper_wkilled_only());
                sx_sunlock(&allproc_lock);
 
                if (p == NULL) {
                        tsleep(&proc0, PVM, "swapin", SWAPIN_INTERVAL);
                } else {
                        PROC_LOCK_ASSERT(p, MA_OWNED);
 
                        /*
                         * Another process may be bringing or may have
                         * already brought this process in while we
                         * traverse all threads.  Or, this process may
                         * have exited or even being swapped out
                         * again.
                         */
                        if (p->p_state == PRS_NORMAL && (p->p_flag & (P_INMEM |
                            P_SWAPPINGOUT | P_SWAPPINGIN)) == 0) {
                                faultin(p);
                        }
                        PROC_UNLOCK(p);
                }
        }
}
 
/*
 * First, if any processes have been sleeping or stopped for at least
 * "swap_idle_threshold1" seconds, they are swapped out.  If, however,
 * no such processes exist, then the longest-sleeping or stopped
 * process is swapped out.  Finally, and only as a last resort, if
 * there are no sleeping or stopped processes, the longest-resident
 * process is swapped out.
 */
static void
swapout_procs(int action)
{
        struct proc *p;
        struct thread *td;
        int slptime;
        bool didswap, doswap;
 
        MPASS((action & (VM_SWAP_NORMAL | VM_SWAP_IDLE)) != 0);
 
        didswap = false;
        sx_slock(&allproc_lock);
        FOREACH_PROC_IN_SYSTEM(p) {
                /*
                 * Filter out not yet fully constructed processes.  Do
                 * not swap out held processes.  Avoid processes which
                 * are system, exiting, execing, traced, already swapped
                 * out or are in the process of being swapped in or out.
                 */
                PROC_LOCK(p);
                if (p->p_state != PRS_NORMAL || p->p_lock != 0 || (p->p_flag &
                    (P_SYSTEM | P_WEXIT | P_INEXEC | P_STOPPED_SINGLE |
                    P_TRACED | P_SWAPPINGOUT | P_SWAPPINGIN | P_INMEM)) !=
                    P_INMEM) {
                        PROC_UNLOCK(p);
                        continue;
                }
 
                /*
                 * Further consideration of this process for swap out
                 * requires iterating over its threads.  We release
                 * allproc_lock here so that process creation and
                 * destruction are not blocked while we iterate.
                 *
                 * To later reacquire allproc_lock and resume
                 * iteration over the allproc list, we will first have
                 * to release the lock on the process.  We place a
                 * hold on the process so that it remains in the
                 * allproc list while it is unlocked.
                 */
                _PHOLD_LITE(p);
                sx_sunlock(&allproc_lock);
 
                /*
                 * Do not swapout a realtime process.
                 * Guarantee swap_idle_threshold1 time in memory.
                 * If the system is under memory stress, or if we are
                 * swapping idle processes >= swap_idle_threshold2,
                 * then swap the process out.
                 */
                doswap = true;
                FOREACH_THREAD_IN_PROC(p, td) {
                        thread_lock(td);
                        slptime = (ticks - td->td_slptick) / hz;
                        if (PRI_IS_REALTIME(td->td_pri_class) ||
                            slptime < swap_idle_threshold1 ||
                            !thread_safetoswapout(td) ||
                            ((action & VM_SWAP_NORMAL) == 0 &&
                            slptime < swap_idle_threshold2))
                                doswap = false;
                        thread_unlock(td);
                        if (!doswap)
                                break;
                }
                if (doswap && swapout(p) == 0)
                        didswap = true;
 
                PROC_UNLOCK(p);
                if (didswap) {
                        sx_xlock(&allproc_lock);
                        swapped_cnt++;
                        sx_downgrade(&allproc_lock);
                } else
                        sx_slock(&allproc_lock);
                PRELE(p);
        }
        sx_sunlock(&allproc_lock);
 
        /*
         * If we swapped something out, and another process needed memory,
         * then wakeup the sched process.
         */
        if (didswap)
                wakeup(&proc0);
}
 
static void
swapclear(struct proc *p)
{
        struct thread *td;
 
        PROC_LOCK_ASSERT(p, MA_OWNED);
 
        FOREACH_THREAD_IN_PROC(p, td) {
                thread_lock(td);
                td->td_flags |= TDF_INMEM;
                td->td_flags &= ~TDF_SWAPINREQ;
                TD_CLR_SWAPPED(td);
                if (TD_CAN_RUN(td)) {
                        if (setrunnable(td, 0)) {
#ifdef INVARIANTS
                                /*
                                 * XXX: We just cleared TDI_SWAPPED
                                 * above and set TDF_INMEM, so this
                                 * should never happen.
                                 */
                                panic("not waking up swapper");
#endif
                        }
                } else
                        thread_unlock(td);
        }
        p->p_flag &= ~(P_SWAPPINGIN | P_SWAPPINGOUT);
        p->p_flag |= P_INMEM;
}
 
static int
swapout(struct proc *p)
{
        struct thread *td;
 
        PROC_LOCK_ASSERT(p, MA_OWNED);
 
        /*
         * The states of this process and its threads may have changed
         * by now.  Assuming that there is only one pageout daemon thread,
         * this process should still be in memory.
         */
        KASSERT((p->p_flag & (P_INMEM | P_SWAPPINGOUT | P_SWAPPINGIN)) ==
            P_INMEM, ("swapout: lost a swapout race?"));
 
        /*
         * Remember the resident count.
         */
        p->p_vmspace->vm_swrss = vmspace_resident_count(p->p_vmspace);
 
        /*
         * Check and mark all threads before we proceed.
         */
        p->p_flag &= ~P_INMEM;
        p->p_flag |= P_SWAPPINGOUT;
        FOREACH_THREAD_IN_PROC(p, td) {
                thread_lock(td);
                if (!thread_safetoswapout(td)) {
                        thread_unlock(td);
                        swapclear(p);
                        return (EBUSY);
                }
                td->td_flags &= ~TDF_INMEM;
                TD_SET_SWAPPED(td);
                thread_unlock(td);
        }
        td = FIRST_THREAD_IN_PROC(p);
        ++td->td_ru.ru_nswap;
        PROC_UNLOCK(p);
 
        /*
         * This list is stable because all threads are now prevented from
         * running.  The list is only modified in the context of a running
         * thread in this process.
         */
        FOREACH_THREAD_IN_PROC(p, td)
                vm_thread_swapout(td);
 
        PROC_LOCK(p);
        p->p_flag &= ~P_SWAPPINGOUT;
        p->p_swtick = ticks;
        return (0);
}