/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*      Copyright (c) 1984, 1986, 1987, 1988, 1989 AT&T */
/*        All Rights Reserved   */

#include <sys/param.h>
#include <sys/types.h>
#include <sys/sysmacros.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/cpuvar.h>
#include <sys/var.h>
#include <sys/tuneable.h>
#include <sys/cmn_err.h>
#include <sys/buf.h>
#include <sys/disp.h>
#include <sys/vmsystm.h>
#include <sys/vmparam.h>
#include <sys/class.h>
#include <sys/vtrace.h>
#include <sys/modctl.h>
#include <sys/debug.h>
#include <sys/sdt.h>
#include <sys/procfs.h>

#include <vm/seg.h>
#include <vm/seg_kp.h>
#include <vm/as.h>
#include <vm/rm.h>
#include <vm/seg_kmem.h>
#include <sys/callb.h>

/*
 * The swapper sleeps on runout when there is no one to swap in.
 * It sleeps on runin when it could not find space to swap someone
 * in or after swapping someone in.
 */
char    runout;
char    runin;
char    wake_sched;     /* flag tells clock to wake swapper on next tick */
char    wake_sched_sec; /* flag tells clock to wake swapper after a second */

/*
 * The swapper swaps processes to reduce memory demand and runs
 * when avefree < desfree.  The swapper resorts to SOFTSWAP when
 * avefree < desfree which results in swapping out all processes
 * sleeping for more than maxslp seconds.  HARDSWAP occurs when the
 * system is on the verge of thrashing and this results in swapping
 * out runnable threads or threads sleeping for less than maxslp secs.
 *
 * The swapper runs through all the active processes in the system
 * and invokes the scheduling class specific swapin/swapout routine
 * for every thread in the process to obtain an effective priority
 * for the process.  A priority of -1 implies that the thread isn't
 * swappable.  This effective priority is used to find the most
 * eligible process to swapout or swapin.
 *
 * NOTE:  Threads which have been swapped are not linked on any
 *        queue and their dispatcher lock points at the "swapped_lock".
 *
 * Processes containing threads with the TS_DONT_SWAP flag set cannot be
 * swapped out immediately by the swapper.  This is due to the fact that
 * such threads may be holding locks which may be needed by the swapper
 * to push its pages out.  The TS_SWAPENQ flag is set on such threads
 * to prevent them running in user mode.  When such threads reach a
 * safe point (i.e., are not holding any locks - CL_TRAPRET), they
 * queue themseleves onto the swap queue which is processed by the
 * swapper.  This results in reducing memory demand when the system
 * is desparate for memory as the thread can't run in user mode.
 *
 * The swap queue consists of threads, linked via t_link, which are
 * haven't been swapped, are runnable but not on the run queue.  The
 * swap queue is protected by the "swapped_lock".  The dispatcher
 * lock (t_lockp) of all threads on the swap queue points at the
 * "swapped_lock".  Thus, the entire queue and/or threads on the
 * queue can be locked by acquiring "swapped_lock".
 */
static kthread_t *tswap_queue;
extern disp_lock_t swapped_lock; /* protects swap queue and threads on it */

int     maxslp = 0;
pgcnt_t avefree;        /* 5 sec moving average of free memory */
pgcnt_t avefree30;      /* 30 sec moving average of free memory */

/*
 * Minimum size used to decide if sufficient memory is available
 * before a process is swapped in.  This is necessary since in most
 * cases the actual size of a process (p_swrss) being swapped in
 * is usually 2 pages (kernel stack pages).  This is due to the fact
 * almost all user pages of a process are stolen by pageout before
 * the swapper decides to swapout it out.
 */
int     min_procsize = 12;

static int      swapin(proc_t *);
static int      swapout(proc_t *, uint_t *, int);
static void     process_swap_queue();

#ifdef __sparc
extern void lwp_swapin(kthread_t *);
#endif /* __sparc */

/*
 * Counters to keep track of the number of swapins or swapouts.
 */
uint_t tot_swapped_in, tot_swapped_out;
uint_t softswap, hardswap, swapqswap;

/*
 * Macro to determine if a process is eligble to be swapped.
 */
#define not_swappable(p)                                        \
        (((p)->p_flag & SSYS) || (p)->p_stat == SIDL ||         \
            (p)->p_stat == SZOMB || (p)->p_as == NULL ||        \
            (p)->p_as == &kas)

/*
 * Memory scheduler.
 */
void
sched()
{
        kthread_id_t    t;
        pri_t           proc_pri;
        pri_t           thread_pri;
        pri_t           swapin_pri;
        int             desperate;
        pgcnt_t         needs;
        int             divisor;
        proc_t          *prp;
        proc_t          *swapout_prp;
        proc_t          *swapin_prp;
        spgcnt_t        avail;
        int             chosen_pri;
        time_t          swapout_time;
        time_t          swapin_proc_time;
        callb_cpr_t     cprinfo;
        kmutex_t        swap_cpr_lock;

        mutex_init(&swap_cpr_lock, NULL, MUTEX_DEFAULT, NULL);
        CALLB_CPR_INIT(&cprinfo, &swap_cpr_lock, callb_generic_cpr, "sched");
        if (maxslp == 0)
                maxslp = MAXSLP;
loop:
        needs = 0;
        desperate = 0;

        swapin_pri = v.v_nglobpris;
        swapin_prp = NULL;
        chosen_pri = -1;

        process_swap_queue();

        /*
         * Set desperate if
         *      1.  At least 2 runnable processes (on average).
         *      2.  Short (5 sec) and longer (30 sec) average is less
         *          than minfree and desfree respectively.
         *      3.  Pagein + pageout rate is excessive.
         */
        if (avenrun[0] >= 2 * FSCALE &&
            (MAX(avefree, avefree30) < desfree) &&
            (pginrate + pgoutrate > maxpgio || avefree < minfree)) {
                TRACE_4(TR_FAC_SCHED, TR_DESPERATE,
                    "desp:avefree: %d, avefree30: %d, freemem: %d"
                    " pginrate: %d\n", avefree, avefree30, freemem, pginrate);
                desperate = 1;
                goto unload;
        }

        /*
         * Search list of processes to swapin and swapout deadwood.
         */
        swapin_proc_time = 0;
top:
        mutex_enter(&pidlock);
        for (prp = practive; prp != NULL; prp = prp->p_next) {
                if (not_swappable(prp))
                        continue;

                /*
                 * Look at processes with at least one swapped lwp.
                 */
                if (prp->p_swapcnt) {
                        time_t proc_time;

                        /*
                         * Higher priority processes are good candidates
                         * to swapin.
                         */
                        mutex_enter(&prp->p_lock);
                        proc_pri = -1;
                        t = prp->p_tlist;
                        proc_time = 0;
                        do {
                                if (t->t_schedflag & TS_LOAD)
                                        continue;

                                thread_lock(t);
                                thread_pri = CL_SWAPIN(t, 0);
                                thread_unlock(t);

                                if (t->t_stime - proc_time > 0)
                                        proc_time = t->t_stime;
                                if (thread_pri > proc_pri)
                                        proc_pri = thread_pri;
                        } while ((t = t->t_forw) != prp->p_tlist);
                        mutex_exit(&prp->p_lock);

                        if (proc_pri == -1)
                                continue;

                        TRACE_3(TR_FAC_SCHED, TR_CHOOSE_SWAPIN,
                            "prp %p epri %d proc_time %d",
                            prp, proc_pri, proc_time);

                        /*
                         * Swapin processes with a high effective priority.
                         */
                        if (swapin_prp == NULL || proc_pri > chosen_pri) {
                                swapin_prp = prp;
                                chosen_pri = proc_pri;
                                swapin_pri = proc_pri;
                                swapin_proc_time = proc_time;
                        }
                } else {
                        /*
                         * No need to soft swap if we have sufficient
                         * memory.
                         */
                        if (avefree > desfree ||
                            avefree < desfree && freemem > desfree)
                                continue;

                        /*
                         * Skip processes that are exiting
                         * or whose address spaces are locked.
                         */
                        mutex_enter(&prp->p_lock);
                        if ((prp->p_flag & SEXITING) ||
                            (prp->p_as != NULL && AS_ISPGLCK(prp->p_as))) {
                                mutex_exit(&prp->p_lock);
                                continue;
                        }

                        /*
                         * Softswapping to kick out deadwood.
                         */
                        proc_pri = -1;
                        t = prp->p_tlist;
                        do {
                                if ((t->t_schedflag & (TS_SWAPENQ |
                                    TS_ON_SWAPQ | TS_LOAD)) != TS_LOAD)
                                        continue;

                                thread_lock(t);
                                thread_pri = CL_SWAPOUT(t, SOFTSWAP);
                                thread_unlock(t);
                                if (thread_pri > proc_pri)
                                        proc_pri = thread_pri;
                        } while ((t = t->t_forw) != prp->p_tlist);

                        if (proc_pri != -1) {
                                uint_t swrss;

                                mutex_exit(&pidlock);

                                TRACE_1(TR_FAC_SCHED, TR_SOFTSWAP,
                                    "softswap:prp %p", prp);

                                (void) swapout(prp, &swrss, SOFTSWAP);
                                softswap++;
                                prp->p_swrss += swrss;
                                mutex_exit(&prp->p_lock);
                                goto top;
                        }
                        mutex_exit(&prp->p_lock);
                }
        }
        if (swapin_prp != NULL)
                mutex_enter(&swapin_prp->p_lock);
        mutex_exit(&pidlock);

        if (swapin_prp == NULL) {
                TRACE_3(TR_FAC_SCHED, TR_RUNOUT,
                "schedrunout:runout nswapped: %d, avefree: %ld freemem: %ld",
                    nswapped, avefree, freemem);

                t = curthread;
                thread_lock(t);
                runout++;
                t->t_schedflag |= (TS_ALLSTART & ~TS_CSTART);
                t->t_whystop = PR_SUSPENDED;
                t->t_whatstop = SUSPEND_NORMAL;
                (void) new_mstate(t, LMS_SLEEP);
                mutex_enter(&swap_cpr_lock);
                CALLB_CPR_SAFE_BEGIN(&cprinfo);
                mutex_exit(&swap_cpr_lock);
                thread_stop(t);         /* change state and drop lock */
                swtch();
                mutex_enter(&swap_cpr_lock);
                CALLB_CPR_SAFE_END(&cprinfo, &swap_cpr_lock);
                mutex_exit(&swap_cpr_lock);
                goto loop;
        }

        /*
         * Decide how deserving this process is to be brought in.
         * Needs is an estimate of how much core the process will
         * need.  If the process has been out for a while, then we
         * will bring it in with 1/2 the core needed, otherwise
         * we are conservative.
         */
        divisor = 1;
        swapout_time = (ddi_get_lbolt() - swapin_proc_time) / hz;
        if (swapout_time > maxslp / 2)
                divisor = 2;

        needs = MIN(swapin_prp->p_swrss, lotsfree);
        needs = MAX(needs, min_procsize);
        needs = needs / divisor;

        /*
         * Use freemem, since we want processes to be swapped
         * in quickly.
         */
        avail = freemem - deficit;
        if (avail > (spgcnt_t)needs) {
                deficit += needs;

                TRACE_2(TR_FAC_SCHED, TR_SWAPIN_VALUES,
                    "swapin_values: prp %p needs %lu", swapin_prp, needs);

                if (swapin(swapin_prp)) {
                        mutex_exit(&swapin_prp->p_lock);
                        goto loop;
                }
                deficit -= MIN(needs, deficit);
                mutex_exit(&swapin_prp->p_lock);
        } else {
                mutex_exit(&swapin_prp->p_lock);
                /*
                 * If deficit is high, too many processes have been
                 * swapped in so wait a sec before attempting to
                 * swapin more.
                 */
                if (freemem > needs) {
                        TRACE_2(TR_FAC_SCHED, TR_HIGH_DEFICIT,
                            "deficit: prp %p needs %lu", swapin_prp, needs);
                        goto block;
                }
        }

        TRACE_2(TR_FAC_SCHED, TR_UNLOAD,
            "unload: prp %p needs %lu", swapin_prp, needs);

unload:
        /*
         * Unload all unloadable modules, free all other memory
         * resources we can find, then look for a thread to hardswap.
         */
        modreap();
        segkp_cache_free();

        swapout_prp = NULL;
        mutex_enter(&pidlock);
        for (prp = practive; prp != NULL; prp = prp->p_next) {

                /*
                 * No need to soft swap if we have sufficient
                 * memory.
                 */
                if (not_swappable(prp))
                        continue;

                if (avefree > minfree ||
                    avefree < minfree && freemem > desfree) {
                        swapout_prp = NULL;
                        break;
                }

                /*
                 * Skip processes that are exiting
                 * or whose address spaces are locked.
                 */
                mutex_enter(&prp->p_lock);
                if ((prp->p_flag & SEXITING) ||
                    (prp->p_as != NULL && AS_ISPGLCK(prp->p_as))) {
                        mutex_exit(&prp->p_lock);
                        continue;
                }

                proc_pri = -1;
                t = prp->p_tlist;
                do {
                        if ((t->t_schedflag & (TS_SWAPENQ |
                            TS_ON_SWAPQ | TS_LOAD)) != TS_LOAD)
                                continue;

                        thread_lock(t);
                        thread_pri = CL_SWAPOUT(t, HARDSWAP);
                        thread_unlock(t);
                        if (thread_pri > proc_pri)
                                proc_pri = thread_pri;
                } while ((t = t->t_forw) != prp->p_tlist);

                mutex_exit(&prp->p_lock);
                if (proc_pri == -1)
                        continue;

                /*
                 * Swapout processes sleeping with a lower priority
                 * than the one currently being swapped in, if any.
                 */
                if (swapin_prp == NULL || swapin_pri > proc_pri) {
                        TRACE_2(TR_FAC_SCHED, TR_CHOOSE_SWAPOUT,
                            "hardswap: prp %p needs %lu", prp, needs);

                        if (swapout_prp == NULL || proc_pri < chosen_pri) {
                                swapout_prp = prp;
                                chosen_pri = proc_pri;
                        }
                }
        }

        /*
         * Acquire the "p_lock" before dropping "pidlock"
         * to prevent the proc structure from being freed
         * if the process exits before swapout completes.
         */
        if (swapout_prp != NULL)
                mutex_enter(&swapout_prp->p_lock);
        mutex_exit(&pidlock);

        if ((prp = swapout_prp) != NULL) {
                uint_t swrss = 0;
                int swapped;

                swapped = swapout(prp, &swrss, HARDSWAP);
                if (swapped) {
                        /*
                         * If desperate, we want to give the space obtained
                         * by swapping this process out to processes in core,
                         * so we give them a chance by increasing deficit.
                         */
                        prp->p_swrss += swrss;
                        if (desperate)
                                deficit += MIN(prp->p_swrss, lotsfree);
                        hardswap++;
                }
                mutex_exit(&swapout_prp->p_lock);

                if (swapped)
                        goto loop;
        }

        /*
         * Delay for 1 second and look again later.
         */
        TRACE_3(TR_FAC_SCHED, TR_RUNIN,
            "schedrunin:runin nswapped: %d, avefree: %ld freemem: %ld",
            nswapped, avefree, freemem);

block:
        t = curthread;
        thread_lock(t);
        runin++;
        t->t_schedflag |= (TS_ALLSTART & ~TS_CSTART);
        t->t_whystop = PR_SUSPENDED;
        t->t_whatstop = SUSPEND_NORMAL;
        (void) new_mstate(t, LMS_SLEEP);
        mutex_enter(&swap_cpr_lock);
        CALLB_CPR_SAFE_BEGIN(&cprinfo);
        mutex_exit(&swap_cpr_lock);
        thread_stop(t);         /* change to stop state and drop lock */
        swtch();
        mutex_enter(&swap_cpr_lock);
        CALLB_CPR_SAFE_END(&cprinfo, &swap_cpr_lock);
        mutex_exit(&swap_cpr_lock);
        goto loop;
}

/*
 * Remove the specified thread from the swap queue.
 */
static void
swapdeq(kthread_id_t tp)
{
        kthread_id_t *tpp;

        ASSERT(THREAD_LOCK_HELD(tp));
        ASSERT(tp->t_schedflag & TS_ON_SWAPQ);

        tpp = &tswap_queue;
        for (;;) {
                ASSERT(*tpp != NULL);
                if (*tpp == tp)
                        break;
                tpp = &(*tpp)->t_link;
        }
        *tpp = tp->t_link;
        tp->t_schedflag &= ~TS_ON_SWAPQ;
}

/*
 * Swap in lwps.  Returns nonzero on success (i.e., if at least one lwp is
 * swapped in) and 0 on failure.
 */
static int
swapin(proc_t *pp)
{
        kthread_id_t tp;
        int err;
        int num_swapped_in = 0;
        struct cpu *cpup = CPU;
        pri_t thread_pri;

        ASSERT(MUTEX_HELD(&pp->p_lock));
        ASSERT(pp->p_swapcnt);

top:
        tp = pp->p_tlist;
        do {
                /*
                 * Only swapin eligible lwps (specified by the scheduling
                 * class) which are unloaded and ready to run.
                 */
                thread_lock(tp);
                thread_pri = CL_SWAPIN(tp, 0);
                if (thread_pri != -1 && tp->t_state == TS_RUN &&
                    (tp->t_schedflag & TS_LOAD) == 0) {
                        size_t stack_size;
                        pgcnt_t stack_pages;

                        ASSERT((tp->t_schedflag & TS_ON_SWAPQ) == 0);

                        thread_unlock(tp);
                        /*
                         * Now drop the p_lock since the stack needs
                         * to brought in.
                         */
                        mutex_exit(&pp->p_lock);

                        stack_size = swapsize(tp->t_swap);
                        stack_pages = btopr(stack_size);

                        /* Kernel probe */
                        DTRACE_SCHED1(swapin__lwp, kthread_t *, tp);

                        rw_enter(&kas.a_lock, RW_READER);
                        err = segkp_fault(segkp->s_as->a_hat, segkp,
                            tp->t_swap, stack_size, F_SOFTLOCK, S_OTHER);
                        rw_exit(&kas.a_lock);

                        /*
                         * Re-acquire the p_lock.
                         */
                        mutex_enter(&pp->p_lock);
                        if (err) {
                                num_swapped_in = 0;
                                break;
                        } else {
#ifdef __sparc
                                lwp_swapin(tp);
#endif /* __sparc */
                                CPU_STATS_ADDQ(cpup, vm, swapin, 1);
                                CPU_STATS_ADDQ(cpup, vm, pgswapin,
                                    stack_pages);

                                pp->p_swapcnt--;
                                pp->p_swrss -= stack_pages;

                                thread_lock(tp);
                                tp->t_schedflag |= TS_LOAD;
                                dq_sruninc(tp);

                                /* set swapin time */
                                tp->t_stime = ddi_get_lbolt();
                                thread_unlock(tp);

                                nswapped--;
                                tot_swapped_in++;
                                num_swapped_in++;

                                TRACE_2(TR_FAC_SCHED, TR_SWAPIN,
                                    "swapin: pp %p stack_pages %lu",
                                    pp, stack_pages);
                                goto top;
                        }
                }
                thread_unlock(tp);
        } while ((tp = tp->t_forw) != pp->p_tlist);
        return (num_swapped_in);
}

/*
 * Swap out lwps.  Returns nonzero on success (i.e., if at least one lwp is
 * swapped out) and 0 on failure.
 */
static int
swapout(proc_t *pp, uint_t *swrss, int swapflags)
{
        kthread_id_t tp;
        pgcnt_t ws_pages = 0;
        int err;
        int swapped_lwps = 0;
        struct as *as = pp->p_as;
        struct cpu *cpup = CPU;
        pri_t thread_pri;

        ASSERT(MUTEX_HELD(&pp->p_lock));

        if (pp->p_flag & SEXITING)
                return (0);

top:
        tp = pp->p_tlist;
        do {
                klwp_t *lwp = ttolwp(tp);

                /*
                 * Swapout eligible lwps (specified by the scheduling
                 * class) which don't have TS_DONT_SWAP set.  Set the
                 * "intent to swap" flag (TS_SWAPENQ) on threads
                 * which have TS_DONT_SWAP set so that they can be
                 * swapped if and when they reach a safe point.
                 */
                thread_lock(tp);
                thread_pri = CL_SWAPOUT(tp, swapflags);
                if (thread_pri != -1) {
                        if (tp->t_schedflag & TS_DONT_SWAP) {
                                tp->t_schedflag |= TS_SWAPENQ;
                                tp->t_trapret = 1;
                                aston(tp);
                        } else {
                                pgcnt_t stack_pages;
                                size_t stack_size;

                                ASSERT((tp->t_schedflag &
                                    (TS_DONT_SWAP | TS_LOAD)) == TS_LOAD);

                                if (lock_try(&tp->t_lock)) {
                                        /*
                                         * Remove thread from the swap_queue.
                                         */
                                        if (tp->t_schedflag & TS_ON_SWAPQ) {
                                                ASSERT(!(tp->t_schedflag &
                                                    TS_SWAPENQ));
                                                swapdeq(tp);
                                        } else if (tp->t_state == TS_RUN)
                                                dq_srundec(tp);

                                        tp->t_schedflag &=
                                            ~(TS_LOAD | TS_SWAPENQ);
                                        lock_clear(&tp->t_lock);

                                        /*
                                         * Set swapout time if the thread isn't
                                         * sleeping.
                                         */
                                        if (tp->t_state != TS_SLEEP)
                                                tp->t_stime = ddi_get_lbolt();
                                        thread_unlock(tp);

                                        nswapped++;
                                        tot_swapped_out++;

                                        lwp->lwp_ru.nswap++;

                                        /*
                                         * Now drop the p_lock since the
                                         * stack needs to pushed out.
                                         */
                                        mutex_exit(&pp->p_lock);

                                        stack_size = swapsize(tp->t_swap);
                                        stack_pages = btopr(stack_size);
                                        ws_pages += stack_pages;

                                        /* Kernel probe */
                                        DTRACE_SCHED1(swapout__lwp,
                                            kthread_t *, tp);

                                        rw_enter(&kas.a_lock, RW_READER);
                                        err = segkp_fault(segkp->s_as->a_hat,
                                            segkp, tp->t_swap, stack_size,
                                            F_SOFTUNLOCK, S_WRITE);
                                        rw_exit(&kas.a_lock);

                                        if (err) {
                                                cmn_err(CE_PANIC,
                                                    "swapout: segkp_fault "
                                                    "failed err: %d", err);
                                        }
                                        CPU_STATS_ADDQ(cpup,
                                            vm, pgswapout, stack_pages);

                                        mutex_enter(&pp->p_lock);
                                        pp->p_swapcnt++;
                                        swapped_lwps++;
                                        goto top;
                                }
                        }
                }
                thread_unlock(tp);
        } while ((tp = tp->t_forw) != pp->p_tlist);

        /*
         * Unload address space when all lwps are swapped out.
         */
        if (pp->p_swapcnt == pp->p_lwpcnt) {
                size_t as_size = 0;

                /*
                 * Avoid invoking as_swapout() if the process has
                 * no MMU resources since pageout will eventually
                 * steal pages belonging to this address space.  This
                 * saves CPU cycles as the number of pages that are
                 * potentially freed or pushed out by the segment
                 * swapout operation is very small.
                 */
                if (rm_asrss(pp->p_as) != 0)
                        as_size = as_swapout(as);

                CPU_STATS_ADDQ(cpup, vm, pgswapout, btop(as_size));
                CPU_STATS_ADDQ(cpup, vm, swapout, 1);
                ws_pages += btop(as_size);

                TRACE_2(TR_FAC_SCHED, TR_SWAPOUT,
                    "swapout: pp %p pages_pushed %lu", pp, ws_pages);

                /* Kernel probe */
                DTRACE_SCHED1(swapout__process, proc_t *, pp);
        }
        *swrss = ws_pages;
        return (swapped_lwps);
}

void
swapout_lwp(klwp_t *lwp)
{
        kthread_id_t tp = curthread;

        ASSERT(curthread == lwptot(lwp));

        /*
         * Don't insert the thread onto the swap queue if
         * sufficient memory is available.
         */
        if (avefree > desfree || avefree < desfree && freemem > desfree) {
                thread_lock(tp);
                tp->t_schedflag &= ~TS_SWAPENQ;
                thread_unlock(tp);
                return;
        }

        /*
         * Lock the thread, then move it to the swapped queue from the
         * onproc queue and set its state to be TS_RUN.
         */
        thread_lock(tp);
        ASSERT(tp->t_state == TS_ONPROC);
        if (tp->t_schedflag & TS_SWAPENQ) {
                tp->t_schedflag &= ~TS_SWAPENQ;

                /*
                 * Set the state of this thread to be runnable
                 * and move it from the onproc queue to the swap queue.
                 */
                disp_swapped_enq(tp);

                /*
                 * Insert the thread onto the swap queue.
                 */
                tp->t_link = tswap_queue;
                tswap_queue = tp;
                tp->t_schedflag |= TS_ON_SWAPQ;

                thread_unlock_nopreempt(tp);

                TRACE_1(TR_FAC_SCHED, TR_SWAPOUT_LWP, "swapout_lwp:%x", lwp);

                swtch();
        } else {
                thread_unlock(tp);
        }
}

/*
 * Swap all threads on the swap queue.
 */
static void
process_swap_queue(void)
{
        kthread_id_t tp;
        uint_t ws_pages;
        proc_t *pp;
        struct cpu *cpup = CPU;
        klwp_t *lwp;
        int err;

        if (tswap_queue == NULL)
                return;

        /*
         * Acquire the "swapped_lock" which locks the swap queue,
         * and unload the stacks of all threads on it.
         */
        disp_lock_enter(&swapped_lock);
        while ((tp = tswap_queue) != NULL) {
                pgcnt_t stack_pages;
                size_t stack_size;

                tswap_queue = tp->t_link;
                tp->t_link = NULL;

                /*
                 * Drop the "dispatcher lock" before acquiring "t_lock"
                 * to avoid spinning on it since the thread at the front
                 * of the swap queue could be pinned before giving up
                 * its "t_lock" in resume.
                 */
                disp_lock_exit(&swapped_lock);
                lock_set(&tp->t_lock);

                /*
                 * Now, re-acquire the "swapped_lock".  Acquiring this lock
                 * results in locking the thread since its dispatcher lock
                 * (t_lockp) is the "swapped_lock".
                 */
                disp_lock_enter(&swapped_lock);
                ASSERT(tp->t_state == TS_RUN);
                ASSERT(tp->t_schedflag & (TS_LOAD | TS_ON_SWAPQ));

                tp->t_schedflag &= ~(TS_LOAD | TS_ON_SWAPQ);
                tp->t_stime = ddi_get_lbolt();          /* swapout time */
                disp_lock_exit(&swapped_lock);
                lock_clear(&tp->t_lock);

                lwp = ttolwp(tp);
                lwp->lwp_ru.nswap++;

                pp = ttoproc(tp);
                stack_size = swapsize(tp->t_swap);
                stack_pages = btopr(stack_size);

                /* Kernel probe */
                DTRACE_SCHED1(swapout__lwp, kthread_t *, tp);

                rw_enter(&kas.a_lock, RW_READER);
                err = segkp_fault(segkp->s_as->a_hat, segkp, tp->t_swap,
                    stack_size, F_SOFTUNLOCK, S_WRITE);
                rw_exit(&kas.a_lock);

                if (err) {
                        cmn_err(CE_PANIC,
                        "process_swap_list: segkp_fault failed err: %d", err);
                }
                CPU_STATS_ADDQ(cpup, vm, pgswapout, stack_pages);

                nswapped++;
                tot_swapped_out++;
                swapqswap++;

                /*
                 * Don't need p_lock since the swapper is the only
                 * thread which increments/decrements p_swapcnt and p_swrss.
                 */
                ws_pages = stack_pages;
                pp->p_swapcnt++;

                TRACE_1(TR_FAC_SCHED, TR_SWAPQ_LWP, "swaplist: pp %p", pp);

                /*
                 * Unload address space when all lwps are swapped out.
                 */
                if (pp->p_swapcnt == pp->p_lwpcnt) {
                        size_t as_size = 0;

                        if (rm_asrss(pp->p_as) != 0)
                                as_size = as_swapout(pp->p_as);

                        CPU_STATS_ADDQ(cpup, vm, pgswapout,
                            btop(as_size));
                        CPU_STATS_ADDQ(cpup, vm, swapout, 1);

                        ws_pages += btop(as_size);

                        TRACE_2(TR_FAC_SCHED, TR_SWAPQ_PROC,
                            "swaplist_proc: pp %p pages_pushed: %lu",
                            pp, ws_pages);

                        /* Kernel probe */
                        DTRACE_SCHED1(swapout__process, proc_t *, pp);
                }
                pp->p_swrss += ws_pages;
                disp_lock_enter(&swapped_lock);
        }
        disp_lock_exit(&swapped_lock);
}