vm_zeroidle.c revision 79265 
1/*-
2 * Copyright (c) 1994 John Dyson
3 * Copyright (c) 2001 Matt Dillon
4 *
5 * All rights reserved.  Terms for use and redistribution
6 * are covered by the BSD Copyright as found in /usr/src/COPYRIGHT.
7 *
8 *	from: @(#)vm_machdep.c	7.3 (Berkeley) 5/13/91
9 *	Utah $Hdr: vm_machdep.c 1.16.1.1 89/06/23$
10 * $FreeBSD: head/sys/vm/vm_zeroidle.c 79265 2001-07-05 01:32:42Z dillon $
11 */
12
13#include "opt_npx.h"
14#ifdef PC98
15#include "opt_pc98.h"
16#endif
17#include "opt_reset.h"
18#include "opt_isa.h"
19
20#include <sys/param.h>
21#include <sys/systm.h>
22#include <sys/malloc.h>
23#include <sys/proc.h>
24#include <sys/bio.h>
25#include <sys/buf.h>
26#include <sys/vnode.h>
27#include <sys/vmmeter.h>
28#include <sys/kernel.h>
29#include <sys/ktr.h>
30#include <sys/mutex.h>
31#include <sys/smp.h>
32#include <sys/sysctl.h>
33#include <sys/unistd.h>
34
35#include <machine/cpu.h>
36#include <machine/md_var.h>
37#include <machine/pcb.h>
38#include <machine/pcb_ext.h>
39#include <machine/vm86.h>
40
41#include <vm/vm.h>
42#include <vm/vm_param.h>
43#include <sys/lock.h>
44#include <vm/vm_kern.h>
45#include <vm/vm_page.h>
46#include <vm/vm_map.h>
47#include <vm/vm_extern.h>
48
49#include <sys/user.h>
50
51#ifdef PC98
52#include <pc98/pc98/pc98.h>
53#else
54#include <i386/isa/isa.h>
55#endif
56
57SYSCTL_DECL(_vm_stats_misc);
58
59static int cnt_prezero;
60
61SYSCTL_INT(_vm_stats_misc, OID_AUTO,
62	cnt_prezero, CTLFLAG_RD, &cnt_prezero, 0, "");
63
64/*
65 * Implement the pre-zeroed page mechanism.
66 * This routine is called from the idle loop.
67 */
68
69#define ZIDLE_LO(v)	((v) * 2 / 3)
70#define ZIDLE_HI(v)	((v) * 4 / 5)
71
72int
73vm_page_zero_idle(void)
74{
75	static int free_rover;
76	static int zero_state;
77	vm_page_t m;
78
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
88	if (zero_state && vm_page_zero_count >= ZIDLE_LO(cnt.v_free_count))
89		return(0);
90	if (vm_page_zero_count >= ZIDLE_HI(cnt.v_free_count))
91		return(0);
92
93	if (mtx_trylock(&Giant)) {
94		zero_state = 0;
95		m = vm_pageq_find(PQ_FREE, free_rover, FALSE);
96		if (m != NULL && (m->flags & PG_ZERO) == 0) {
97			vm_page_queues[m->queue].lcnt--;
98			TAILQ_REMOVE(&vm_page_queues[m->queue].pl, m, pageq);
99			m->queue = PQ_NONE;
100			pmap_zero_page(VM_PAGE_TO_PHYS(m));
101			vm_page_flag_set(m, PG_ZERO);
102			m->queue = PQ_FREE + m->pc;
103			vm_page_queues[m->queue].lcnt++;
104			TAILQ_INSERT_TAIL(&vm_page_queues[m->queue].pl, m,
105			    pageq);
106			++vm_page_zero_count;
107			++cnt_prezero;
108			if (vm_page_zero_count >= ZIDLE_HI(cnt.v_free_count))
109				zero_state = 1;
110		}
111		free_rover = (free_rover + PQ_PRIME2) & PQ_L2_MASK;
112		mtx_unlock(&Giant);
113		return (1);
114	}
115	return(0);
116}
117
118