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/*-
* Copyright (c) 1994 John Dyson
* Copyright (c) 2001 Matt Dillon
*
* All rights reserved. Terms for use and redistribution
* are covered by the BSD Copyright as found in /usr/src/COPYRIGHT.
*
* from: @(#)vm_machdep.c 7.3 (Berkeley) 5/13/91
* Utah $Hdr: vm_machdep.c 1.16.1.1 89/06/23$
* $FreeBSD$
*/
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/resourcevar.h>
#include <sys/vmmeter.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/sysctl.h>
#include <sys/kthread.h>
#include <vm/vm.h>
#include <vm/vm_page.h>
SYSCTL_DECL(_vm_stats_misc);
static int cnt_prezero;
SYSCTL_INT(_vm_stats_misc, OID_AUTO,
cnt_prezero, CTLFLAG_RD, &cnt_prezero, 0, "");
static int idlezero_enable = 0;
SYSCTL_INT(_vm, OID_AUTO, idlezero_enable, CTLFLAG_RW, &idlezero_enable, 0, "");
TUNABLE_INT("vm.idlezero_enable", &idlezero_enable);
static int idlezero_maxrun = 16;
SYSCTL_INT(_vm, OID_AUTO, idlezero_maxrun, CTLFLAG_RW, &idlezero_maxrun, 0, "");
TUNABLE_INT("vm.idlezero_maxrun", &idlezero_maxrun);
/*
* Implement the pre-zeroed page mechanism.
*/
#define ZIDLE_LO(v) ((v) * 2 / 3)
#define ZIDLE_HI(v) ((v) * 4 / 5)
static int zero_state;
static int
vm_page_zero_check(void)
{
if (!idlezero_enable)
return 0;
/*
* Attempt to maintain approximately 1/2 of our free pages in a
* PG_ZERO'd state. Add some hysteresis to (attempt to) avoid
* generally zeroing a page when the system is near steady-state.
* Otherwise we might get 'flutter' during disk I/O / IPC or
* fast sleeps. We also do not want to be continuously zeroing
* pages because doing so may flush our L1 and L2 caches too much.
*/
if (zero_state && vm_page_zero_count >= ZIDLE_LO(cnt.v_free_count))
return 0;
if (vm_page_zero_count >= ZIDLE_HI(cnt.v_free_count))
return 0;
return 1;
}
static int
vm_page_zero_idle(void)
{
static int free_rover;
vm_page_t m;
mtx_lock(&Giant);
zero_state = 0;
m = vm_pageq_find(PQ_FREE, free_rover, FALSE);
if (m != NULL && (m->flags & PG_ZERO) == 0) {
vm_page_queues[m->queue].lcnt--;
TAILQ_REMOVE(&vm_page_queues[m->queue].pl, m, pageq);
m->queue = PQ_NONE;
/* maybe drop out of Giant here */
pmap_zero_page(m);
/* and return here */
vm_page_flag_set(m, PG_ZERO);
m->queue = PQ_FREE + m->pc;
vm_page_queues[m->queue].lcnt++;
TAILQ_INSERT_TAIL(&vm_page_queues[m->queue].pl, m,
pageq);
++vm_page_zero_count;
++cnt_prezero;
if (vm_page_zero_count >= ZIDLE_HI(cnt.v_free_count))
zero_state = 1;
}
free_rover = (free_rover + PQ_PRIME2) & PQ_L2_MASK;
mtx_unlock(&Giant);
return 1;
}
/* Called by vm_page_free to hint that a new page is available */
void
vm_page_zero_idle_wakeup(void)
{
if (vm_page_zero_check())
wakeup(&zero_state);
}
static void
vm_pagezero(void)
{
struct thread *td = curthread;
struct rtprio rtp;
int pages = 0;
rtp.prio = RTP_PRIO_MAX;
rtp.type = RTP_PRIO_IDLE;
mtx_lock_spin(&sched_lock);
rtp_to_pri(&rtp, td->td_ksegrp);
mtx_unlock_spin(&sched_lock);
for (;;) {
if (vm_page_zero_check()) {
pages += vm_page_zero_idle();
if (pages > idlezero_maxrun) {
mtx_lock_spin(&sched_lock);
setrunqueue(td);
td->td_proc->p_stats->p_ru.ru_nvcsw++;
mi_switch();
mtx_unlock_spin(&sched_lock);
pages = 0;
}
} else {
tsleep(&zero_state, PPAUSE, "pgzero", hz * 300);
pages = 0;
}
}
}
static struct proc *pagezero;
static struct kproc_desc pagezero_kp = {
"pagezero",
vm_pagezero,
&pagezero
};
SYSINIT(pagezero, SI_SUB_KTHREAD_VM, SI_ORDER_ANY, kproc_start, &pagezero_kp)
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