Home Home > GIT Browse
summaryrefslogtreecommitdiff
blob: 2372d4ed5dd8ff763d3aaed5cb546c8033eca1ff (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
/*
 * mm/thrash.c
 *
 * Copyright (C) 2004, Red Hat, Inc.
 * Copyright (C) 2004, Rik van Riel <riel@redhat.com>
 * Released under the GPL, see the file COPYING for details.
 *
 * Simple token based thrashing protection, using the algorithm
 * described in:  http://www.cs.wm.edu/~sjiang/token.pdf
 *
 * Sep 2006, Ashwin Chaugule <ashwin.chaugule@celunite.com>
 * Improved algorithm to pass token:
 * Each task has a priority which is incremented if it contended
 * for the token in an interval less than its previous attempt.
 * If the token is acquired, that task's priority is boosted to prevent
 * the token from bouncing around too often and to let the task make
 * some progress in its execution.
 */

#include <linux/jiffies.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/swap.h>

static DEFINE_SPINLOCK(swap_token_lock);
struct mm_struct *swap_token_mm;
static unsigned int global_faults;

void grab_swap_token(struct mm_struct *mm)
{
	int current_interval;

	global_faults++;

	current_interval = global_faults - mm->faultstamp;

	if (!spin_trylock(&swap_token_lock))
		return;

	/* First come first served */
	if (swap_token_mm == NULL) {
		mm->token_priority = mm->token_priority + 2;
		swap_token_mm = mm;
		goto out;
	}

	if (mm != swap_token_mm) {
		if (current_interval < mm->last_interval)
			mm->token_priority++;
		else {
			if (likely(mm->token_priority > 0))
				mm->token_priority--;
		}
		/* Check if we deserve the token */
		if (mm->token_priority > swap_token_mm->token_priority) {
			mm->token_priority += 2;
			swap_token_mm = mm;
		}
	} else {
		/* Token holder came in again! */
		mm->token_priority += 2;
	}

out:
	mm->faultstamp = global_faults;
	mm->last_interval = current_interval;
	spin_unlock(&swap_token_lock);
}

/* Called on process exit. */
void __put_swap_token(struct mm_struct *mm)
{
	spin_lock(&swap_token_lock);
	if (likely(mm == swap_token_mm))
		swap_token_mm = NULL;
	spin_unlock(&swap_token_lock);
}