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
25 static DEFINE_SPINLOCK(swap_token_lock);
26 struct mm_struct *swap_token_mm;
27 static unsigned int global_faults;
28
29 void 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
64 out:
65 mm->faultstamp = global_faults;
66 mm->last_interval = current_interval;
67 spin_unlock(&swap_token_lock);
68 }
69
70 /* Called on process exit. */
71 void __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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