1/*- 2 * Copyright (c) 1994 John Dyson 3 * Copyright (c) 2001 Matt Dillon 4 * 5 * All Rights Reserved. 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 4. Neither the name of the University nor the names of its contributors 15 * may be used to endorse or promote products derived from this software 16 * without specific prior written permission. 17 * 18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS 19 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 20 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY 22 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE 24 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 26 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING 27 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 28 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 29 * 30 * from: @(#)vm_machdep.c 7.3 (Berkeley) 5/13/91 31 * Utah $Hdr: vm_machdep.c 1.16.1.1 89/06/23$ 32 * from: FreeBSD: .../i386/vm_machdep.c,v 1.165 2001/07/04 23:27:04 dillon 33 */ 34 35#include <sys/cdefs.h> 36__FBSDID("$FreeBSD$"); 37 38#include <opt_sched.h> 39 40#include <sys/param.h> 41#include <sys/systm.h> 42#include <sys/kernel.h> 43#include <sys/proc.h> 44#include <sys/vmmeter.h> 45#include <sys/lock.h> 46#include <sys/mutex.h> 47#include <sys/sched.h> 48#include <sys/sysctl.h> 49#include <sys/kthread.h> 50#include <sys/unistd.h> 51 52#include <vm/vm.h> 53#include <vm/vm_param.h> 54#include <vm/vm_page.h> 55#include <vm/vm_phys.h> 56 57static int idlezero_enable_default = 0; 58TUNABLE_INT("vm.idlezero_enable", &idlezero_enable_default); 59/* Defer setting the enable flag until the kthread is running. */ 60static int idlezero_enable = 0; 61SYSCTL_INT(_vm, OID_AUTO, idlezero_enable, CTLFLAG_RW, &idlezero_enable, 0, 62 "Allow the kernel to use idle cpu cycles to zero-out pages"); 63/* 64 * Implement the pre-zeroed page mechanism. 65 */ 66 67#define ZIDLE_LO(v) ((v) * 2 / 3) 68#define ZIDLE_HI(v) ((v) * 4 / 5) 69 70static boolean_t wakeup_needed = FALSE; 71static int zero_state; 72 73static int 74vm_page_zero_check(void) 75{ 76 77 if (!idlezero_enable) 78 return (0); 79 /* 80 * Attempt to maintain approximately 1/2 of our free pages in a 81 * PG_ZERO'd state. Add some hysteresis to (attempt to) avoid 82 * generally zeroing a page when the system is near steady-state. 83 * Otherwise we might get 'flutter' during disk I/O / IPC or 84 * fast sleeps. We also do not want to be continuously zeroing 85 * pages because doing so may flush our L1 and L2 caches too much. 86 */ 87 if (zero_state && vm_page_zero_count >= ZIDLE_LO(cnt.v_free_count)) 88 return (0); 89 if (vm_page_zero_count >= ZIDLE_HI(cnt.v_free_count)) 90 return (0); 91 return (1); 92} 93 94static void 95vm_page_zero_idle(void) 96{ 97 98 mtx_assert(&vm_page_queue_free_mtx, MA_OWNED); 99 zero_state = 0; 100 if (vm_phys_zero_pages_idle()) { 101 if (vm_page_zero_count >= ZIDLE_HI(cnt.v_free_count)) 102 zero_state = 1; 103 } 104} 105 106/* Called by vm_page_free to hint that a new page is available. */ 107void 108vm_page_zero_idle_wakeup(void) 109{ 110 111 mtx_assert(&vm_page_queue_free_mtx, MA_OWNED); 112 if (wakeup_needed && vm_page_zero_check()) { 113 wakeup_needed = FALSE; 114 wakeup(&zero_state); 115 } 116} 117 118static void 119vm_pagezero(void __unused *arg) 120{ 121 122 idlezero_enable = idlezero_enable_default; 123 124 mtx_lock(&vm_page_queue_free_mtx); 125 for (;;) { 126 if (vm_page_zero_check()) { 127 vm_page_zero_idle(); 128#ifndef PREEMPTION 129 if (sched_runnable()) { 130 thread_lock(curthread); 131 mi_switch(SW_VOL | SWT_IDLE, NULL); 132 thread_unlock(curthread); 133 } 134#endif 135 } else { 136 wakeup_needed = TRUE; 137 msleep(&zero_state, &vm_page_queue_free_mtx, 0, 138 "pgzero", hz * 300); 139 } 140 } 141} 142 143static void 144pagezero_start(void __unused *arg) 145{ 146 int error; 147 struct proc *p; 148 struct thread *td; 149 150 error = kproc_create(vm_pagezero, NULL, &p, RFSTOPPED, 0, "pagezero"); 151 if (error) 152 panic("pagezero_start: error %d\n", error); 153 td = FIRST_THREAD_IN_PROC(p); 154 thread_lock(td); 155 156 /* We're an idle task, don't count us in the load. */ 157 td->td_flags |= TDF_NOLOAD; 158 sched_class(td, PRI_IDLE); 159 sched_prio(td, PRI_MAX_IDLE); 160 sched_add(td, SRQ_BORING); 161 thread_unlock(td); 162} 163SYSINIT(pagezero, SI_SUB_KTHREAD_VM, SI_ORDER_ANY, pagezero_start, NULL); 164