Root/mm/thrash.c

1/*
2 * mm/thrash.c
3 *
4 * Copyright (C) 2004, Red Hat, Inc.
5 * Copyright (C) 2004, Rik van Riel <riel@redhat.com>
6 * Released under the GPL, see the file COPYING for details.
7 *
8 * Simple token based thrashing protection, using the algorithm
9 * described in: http://www.cs.wm.edu/~sjiang/token.pdf
10 *
11 * Sep 2006, Ashwin Chaugule <ashwin.chaugule@celunite.com>
12 * Improved algorithm to pass token:
13 * Each task has a priority which is incremented if it contended
14 * for the token in an interval less than its previous attempt.
15 * If the token is acquired, that task's priority is boosted to prevent
16 * the token from bouncing around too often and to let the task make
17 * some progress in its execution.
18 */
19
20#include <linux/jiffies.h>
21#include <linux/mm.h>
22#include <linux/sched.h>
23#include <linux/swap.h>
24
25static DEFINE_SPINLOCK(swap_token_lock);
26struct mm_struct *swap_token_mm;
27static unsigned int global_faults;
28
29void grab_swap_token(struct mm_struct *mm)
30{
31    int current_interval;
32
33    global_faults++;
34
35    current_interval = global_faults - mm->faultstamp;
36
37    if (!spin_trylock(&swap_token_lock))
38        return;
39
40    /* First come first served */
41    if (swap_token_mm == NULL) {
42        mm->token_priority = mm->token_priority + 2;
43        swap_token_mm = mm;
44        goto out;
45    }
46
47    if (mm != swap_token_mm) {
48        if (current_interval < mm->last_interval)
49            mm->token_priority++;
50        else {
51            if (likely(mm->token_priority > 0))
52                mm->token_priority--;
53        }
54        /* Check if we deserve the token */
55        if (mm->token_priority > swap_token_mm->token_priority) {
56            mm->token_priority += 2;
57            swap_token_mm = mm;
58        }
59    } else {
60        /* Token holder came in again! */
61        mm->token_priority += 2;
62    }
63
64out:
65    mm->faultstamp = global_faults;
66    mm->last_interval = current_interval;
67    spin_unlock(&swap_token_lock);
68}
69
70/* Called on process exit. */
71void __put_swap_token(struct mm_struct *mm)
72{
73    spin_lock(&swap_token_lock);
74    if (likely(mm == swap_token_mm))
75        swap_token_mm = NULL;
76    spin_unlock(&swap_token_lock);
77}
78

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