2 * Copyright (c) 1994 John Dyson
3 * Copyright (c) 2001 Matt Dillon
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
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.
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.
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
35 #include <sys/cdefs.h>
36 __FBSDID("$FreeBSD$");
38 #include <opt_sched.h>
40 #include <sys/param.h>
41 #include <sys/systm.h>
42 #include <sys/kernel.h>
44 #include <sys/vmmeter.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>
53 #include <vm/vm_page.h>
55 static int cnt_prezero;
56 SYSCTL_INT(_vm_stats_misc, OID_AUTO, cnt_prezero, CTLFLAG_RD,
59 static int idlezero_enable_default = 1;
60 TUNABLE_INT("vm.idlezero_enable", &idlezero_enable_default);
61 /* Defer setting the enable flag until the kthread is running. */
62 static int idlezero_enable = 0;
63 SYSCTL_INT(_vm, OID_AUTO, idlezero_enable, CTLFLAG_RW, &idlezero_enable, 0, "");
65 static int idlezero_maxrun = 16;
66 SYSCTL_INT(_vm, OID_AUTO, idlezero_maxrun, CTLFLAG_RW, &idlezero_maxrun, 0, "");
67 TUNABLE_INT("vm.idlezero_maxrun", &idlezero_maxrun);
70 * Implement the pre-zeroed page mechanism.
73 #define ZIDLE_LO(v) ((v) * 2 / 3)
74 #define ZIDLE_HI(v) ((v) * 4 / 5)
76 static boolean_t wakeup_needed = FALSE;
77 static int zero_state;
80 vm_page_zero_check(void)
86 * Attempt to maintain approximately 1/2 of our free pages in a
87 * PG_ZERO'd state. Add some hysteresis to (attempt to) avoid
88 * generally zeroing a page when the system is near steady-state.
89 * Otherwise we might get 'flutter' during disk I/O / IPC or
90 * fast sleeps. We also do not want to be continuously zeroing
91 * pages because doing so may flush our L1 and L2 caches too much.
93 if (zero_state && vm_page_zero_count >= ZIDLE_LO(cnt.v_free_count))
95 if (vm_page_zero_count >= ZIDLE_HI(cnt.v_free_count))
101 vm_page_zero_idle(void)
103 static int free_rover;
106 mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
108 m = vm_pageq_find(PQ_FREE, free_rover, FALSE);
109 if (m != NULL && (m->flags & PG_ZERO) == 0) {
110 vm_pageq_remove_nowakeup(m);
111 mtx_unlock(&vm_page_queue_free_mtx);
112 pmap_zero_page_idle(m);
113 mtx_lock(&vm_page_queue_free_mtx);
115 vm_pageq_enqueue(PQ_FREE + m->pc, m);
116 ++vm_page_zero_count;
118 if (vm_page_zero_count >= ZIDLE_HI(cnt.v_free_count))
121 free_rover = (free_rover + PQ_PRIME2) & PQ_COLORMASK;
124 /* Called by vm_page_free to hint that a new page is available. */
126 vm_page_zero_idle_wakeup(void)
129 mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
130 if (wakeup_needed && vm_page_zero_check()) {
131 wakeup_needed = FALSE;
137 vm_pagezero(void __unused *arg)
140 idlezero_enable = idlezero_enable_default;
142 mtx_lock(&vm_page_queue_free_mtx);
144 if (vm_page_zero_check()) {
147 if (sched_runnable()) {
148 mtx_lock_spin(&sched_lock);
149 mi_switch(SW_VOL, NULL);
150 mtx_unlock_spin(&sched_lock);
154 wakeup_needed = TRUE;
155 msleep(&zero_state, &vm_page_queue_free_mtx, 0,
161 static struct proc *pagezero_proc;
164 pagezero_start(void __unused *arg)
169 error = kthread_create(vm_pagezero, NULL, &pagezero_proc, RFSTOPPED, 0,
172 panic("pagezero_start: error %d\n", error);
174 * We're an idle task, don't count us in the load.
176 PROC_LOCK(pagezero_proc);
177 pagezero_proc->p_flag |= P_NOLOAD;
178 PROC_UNLOCK(pagezero_proc);
179 mtx_lock_spin(&sched_lock);
180 td = FIRST_THREAD_IN_PROC(pagezero_proc);
181 sched_class(td, PRI_IDLE);
182 sched_prio(td, PRI_MAX_IDLE);
183 sched_add(td, SRQ_BORING);
184 mtx_unlock_spin(&sched_lock);
186 SYSINIT(pagezero, SI_SUB_KTHREAD_VM, SI_ORDER_ANY, pagezero_start, NULL)