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 #include <linux/jiffies.h>
12 #include <linux/mm.h>
13 #include <linux/sched.h>
14 #include <linux/swap.h>
15
16 static DEFINE_SPINLOCK(swap_token_lock);
17 static unsigned long swap_token_timeout;
18 static unsigned long swap_token_check;
19 struct mm_struct * swap_token_mm = &init_mm;
20
21 #define SWAP_TOKEN_CHECK_INTERVAL (HZ * 2)
22 #define SWAP_TOKEN_TIMEOUT (300 * HZ)
23 /*
24 * Currently disabled; Needs further code to work at HZ * 300.
25 */
26 unsigned long swap_token_default_timeout = SWAP_TOKEN_TIMEOUT;
27
28 /*
29 * Take the token away if the process had no page faults
30 * in the last interval, or if it has held the token for
31 * too long.
32 */
33 #define SWAP_TOKEN_ENOUGH_RSS 1
34 #define SWAP_TOKEN_TIMED_OUT 2
35 static int should_release_swap_token(struct mm_struct *mm)
36 {
37 int ret = 0;
38 if (!mm->recent_pagein)
39 ret = SWAP_TOKEN_ENOUGH_RSS;
40 else if (time_after(jiffies, swap_token_timeout))
41 ret = SWAP_TOKEN_TIMED_OUT;
42 mm->recent_pagein = 0;
43 return ret;
44 }
45
46 /*
47 * Try to grab the swapout protection token. We only try to
48 * grab it once every TOKEN_CHECK_INTERVAL, both to prevent
49 * SMP lock contention and to check that the process that held
50 * the token before is no longer thrashing.
51 */
52 void grab_swap_token(void)
53 {
54 struct mm_struct *mm;
55 int reason;
56
57 /* We have the token. Let others know we still need it. */
58 if (has_swap_token(current->mm)) {
59 current->mm->recent_pagein = 1;
60 if (unlikely(!swap_token_default_timeout))
61 disable_swap_token();
62 return;
63 }
64
65 if (time_after(jiffies, swap_token_check)) {
66
67 if (!swap_token_default_timeout) {
68 swap_token_check = jiffies + SWAP_TOKEN_CHECK_INTERVAL;
69 return;
70 }
71
72 /* ... or if we recently held the token. */
73 if (time_before(jiffies, current->mm->swap_token_time))
74 return;
75
76 if (!spin_trylock(&swap_token_lock))
77 return;
78
79 swap_token_check = jiffies + SWAP_TOKEN_CHECK_INTERVAL;
80
81 mm = swap_token_mm;
82 if ((reason = should_release_swap_token(mm))) {
83 unsigned long eligible = jiffies;
84 if (reason == SWAP_TOKEN_TIMED_OUT) {
85 eligible += swap_token_default_timeout;
86 }
87 mm->swap_token_time = eligible;
88 swap_token_timeout = jiffies + swap_token_default_timeout;
89 swap_token_mm = current->mm;
90 }
91 spin_unlock(&swap_token_lock);
92 }
93 return;
94 }
95
96 /* Called on process exit. */
97 void __put_swap_token(struct mm_struct *mm)
98 {
99 spin_lock(&swap_token_lock);
100 if (likely(mm == swap_token_mm)) {
101 mm->swap_token_time = jiffies + SWAP_TOKEN_CHECK_INTERVAL;
102 swap_token_mm = &init_mm;
103 swap_token_check = jiffies;
104 }
105 spin_unlock(&swap_token_lock);
106 }
107
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