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
57 static int idlezero_enable_default = 0;
58 /* Defer setting the enable flag until the kthread is running. */
59 static int idlezero_enable = 0;
60 SYSCTL_INT(_vm, OID_AUTO, idlezero_enable, CTLFLAG_RWTUN, &idlezero_enable, 0,
61 "Allow the kernel to use idle cpu cycles to zero-out pages");
62 /*
63 * Implement the pre-zeroed page mechanism.
64 */
65
66 #define ZIDLE_LO(v) ((v) * 2 / 3)
67 #define ZIDLE_HI(v) ((v) * 4 / 5)
68
69 static boolean_t wakeup_needed = FALSE;
70 static int zero_state;
71
72 static int
vm_page_zero_check(void)73 vm_page_zero_check(void)
74 {
75
76 if (!idlezero_enable)
77 return (0);
78 /*
79 * Attempt to maintain approximately 1/2 of our free pages in a
80 * PG_ZERO'd state. Add some hysteresis to (attempt to) avoid
81 * generally zeroing a page when the system is near steady-state.
82 * Otherwise we might get 'flutter' during disk I/O / IPC or
83 * fast sleeps. We also do not want to be continuously zeroing
84 * pages because doing so may flush our L1 and L2 caches too much.
85 */
86 if (zero_state && vm_page_zero_count >= ZIDLE_LO(vm_cnt.v_free_count))
87 return (0);
88 if (vm_page_zero_count >= ZIDLE_HI(vm_cnt.v_free_count))
89 return (0);
90 return (1);
91 }
92
93 static void
vm_page_zero_idle(void)94 vm_page_zero_idle(void)
95 {
96
97 mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
98 zero_state = 0;
99 if (vm_phys_zero_pages_idle()) {
100 if (vm_page_zero_count >= ZIDLE_HI(vm_cnt.v_free_count))
101 zero_state = 1;
102 }
103 }
104
105 /* Called by vm_page_free to hint that a new page is available. */
106 void
vm_page_zero_idle_wakeup(void)107 vm_page_zero_idle_wakeup(void)
108 {
109
110 mtx_assert(&vm_page_queue_free_mtx, MA_OWNED);
111 if (wakeup_needed && vm_page_zero_check()) {
112 wakeup_needed = FALSE;
113 wakeup(&zero_state);
114 }
115 }
116
117 static void
vm_pagezero(void __unused * arg)118 vm_pagezero(void __unused *arg)
119 {
120
121 idlezero_enable = idlezero_enable_default;
122
123 mtx_lock(&vm_page_queue_free_mtx);
124 for (;;) {
125 if (vm_page_zero_check()) {
126 vm_page_zero_idle();
127 #ifndef PREEMPTION
128 if (sched_runnable()) {
129 thread_lock(curthread);
130 mi_switch(SW_VOL | SWT_IDLE, NULL);
131 thread_unlock(curthread);
132 }
133 #endif
134 } else {
135 wakeup_needed = TRUE;
136 msleep(&zero_state, &vm_page_queue_free_mtx, 0,
137 "pgzero", hz * 300);
138 }
139 }
140 }
141
142 static void
pagezero_start(void __unused * arg)143 pagezero_start(void __unused *arg)
144 {
145 int error;
146 struct proc *p;
147 struct thread *td;
148
149 error = kproc_create(vm_pagezero, NULL, &p, RFSTOPPED, 0, "pagezero");
150 if (error)
151 panic("pagezero_start: error %d\n", error);
152 td = FIRST_THREAD_IN_PROC(p);
153 thread_lock(td);
154
155 /* We're an idle task, don't count us in the load. */
156 td->td_flags |= TDF_NOLOAD;
157 sched_class(td, PRI_IDLE);
158 sched_prio(td, PRI_MAX_IDLE);
159 sched_add(td, SRQ_BORING);
160 thread_unlock(td);
161 }
162 SYSINIT(pagezero, SI_SUB_KTHREAD_VM, SI_ORDER_ANY, pagezero_start, NULL);
163