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_page.h>
54#include <vm/vm_phys.h>
55
56static int idlezero_enable_default = 0;
57TUNABLE_INT("vm.idlezero_enable", &idlezero_enable_default);
58/* Defer setting the enable flag until the kthread is running. */
59static int idlezero_enable = 0;
60SYSCTL_INT(_vm, OID_AUTO, idlezero_enable, CTLFLAG_RW, &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
69static boolean_t wakeup_needed = FALSE;
70static int zero_state;
71
72static int
73vm_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(cnt.v_free_count))
87		return (0);
88	if (vm_page_zero_count >= ZIDLE_HI(cnt.v_free_count))
89		return (0);
90	return (1);
91}
92
93static void
94vm_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(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. */
106void
107vm_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
117static void
118vm_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
142static void
143pagezero_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}
162SYSINIT(pagezero, SI_SUB_KTHREAD_VM, SI_ORDER_ANY, pagezero_start, NULL);
163