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