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/*-
* Copyright (c) 1994 John Dyson
* Copyright (c) 2001 Matt Dillon
*
* All Rights Reserved.
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 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 AUTHOR ``AS IS'' AND ANY EXPRESS
* OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
* GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* from: @(#)vm_machdep.c 7.3 (Berkeley) 5/13/91
* Utah $Hdr: vm_machdep.c 1.16.1.1 89/06/23$
* from: FreeBSD: .../i386/vm_machdep.c,v 1.165 2001/07/04 23:27:04 dillon
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <opt_sched.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/vmmeter.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/sched.h>
#include <sys/sysctl.h>
#include <sys/kthread.h>
#include <sys/unistd.h>
#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/vm_page.h>
#include <vm/vm_phys.h>
static int idlezero_enable_default = 0;
TUNABLE_INT("vm.idlezero_enable", &idlezero_enable_default);
/* Defer setting the enable flag until the kthread is running. */
static int idlezero_enable = 0;
SYSCTL_INT(_vm, OID_AUTO, idlezero_enable, CTLFLAG_RW, &idlezero_enable, 0,
"Allow the kernel to use idle cpu cycles to zero-out pages");
/*
* Implement the pre-zeroed page mechanism.
*/
#define ZIDLE_LO(v) ((v) * 2 / 3)
#define ZIDLE_HI(v) ((v) * 4 / 5)
static boolean_t wakeup_needed = FALSE;
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(vm_cnt.v_free_count))
return (0);
if (vm_page_zero_count >= ZIDLE_HI(vm_cnt.v_free_count))
return (0);
return (1);
}
static void
vm_page_zero_idle(void)
{
mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
zero_state = 0;
if (vm_phys_zero_pages_idle()) {
if (vm_page_zero_count >= ZIDLE_HI(vm_cnt.v_free_count))
zero_state = 1;
}
}
/* Called by vm_page_free to hint that a new page is available. */
void
vm_page_zero_idle_wakeup(void)
{
mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
if (wakeup_needed && vm_page_zero_check()) {
wakeup_needed = FALSE;
wakeup(&zero_state);
}
}
static void
vm_pagezero(void __unused *arg)
{
idlezero_enable = idlezero_enable_default;
mtx_lock(&vm_page_queue_free_mtx);
for (;;) {
if (vm_page_zero_check()) {
vm_page_zero_idle();
#ifndef PREEMPTION
if (sched_runnable()) {
thread_lock(curthread);
mi_switch(SW_VOL | SWT_IDLE, NULL);
thread_unlock(curthread);
}
#endif
} else {
wakeup_needed = TRUE;
msleep(&zero_state, &vm_page_queue_free_mtx, 0,
"pgzero", hz * 300);
}
}
}
static void
pagezero_start(void __unused *arg)
{
int error;
struct proc *p;
struct thread *td;
error = kproc_create(vm_pagezero, NULL, &p, RFSTOPPED, 0, "pagezero");
if (error)
panic("pagezero_start: error %d\n", error);
td = FIRST_THREAD_IN_PROC(p);
thread_lock(td);
/* We're an idle task, don't count us in the load. */
td->td_flags |= TDF_NOLOAD;
sched_class(td, PRI_IDLE);
sched_prio(td, PRI_MAX_IDLE);
sched_add(td, SRQ_BORING);
thread_unlock(td);
}
SYSINIT(pagezero, SI_SUB_KTHREAD_VM, SI_ORDER_ANY, pagezero_start, NULL);
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