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#include <linux/memcontrol.h>
25
26#include <trace/events/vmscan.h>
27
28#define TOKEN_AGING_INTERVAL (0xFF)
29
30static DEFINE_SPINLOCK(swap_token_lock);
31struct mm_struct *swap_token_mm;
32struct mem_cgroup *swap_token_memcg;
33static unsigned int global_faults;
34static unsigned int last_aging;
35
36#ifdef CONFIG_CGROUP_MEM_RES_CTLR
37static struct mem_cgroup *swap_token_memcg_from_mm(struct mm_struct *mm)
38{
39    struct mem_cgroup *memcg;
40
41    memcg = try_get_mem_cgroup_from_mm(mm);
42    if (memcg)
43        css_put(mem_cgroup_css(memcg));
44
45    return memcg;
46}
47#else
48static struct mem_cgroup *swap_token_memcg_from_mm(struct mm_struct *mm)
49{
50    return NULL;
51}
52#endif
53
54void grab_swap_token(struct mm_struct *mm)
55{
56    int current_interval;
57    unsigned int old_prio = mm->token_priority;
58
59    global_faults++;
60
61    current_interval = global_faults - mm->faultstamp;
62
63    if (!spin_trylock(&swap_token_lock))
64        return;
65
66    /* First come first served */
67    if (!swap_token_mm)
68        goto replace_token;
69
70    if ((global_faults - last_aging) > TOKEN_AGING_INTERVAL) {
71        swap_token_mm->token_priority /= 2;
72        last_aging = global_faults;
73    }
74
75    if (mm == swap_token_mm) {
76        mm->token_priority += 2;
77        goto update_priority;
78    }
79
80    if (current_interval < mm->last_interval)
81        mm->token_priority++;
82    else {
83        if (likely(mm->token_priority > 0))
84            mm->token_priority--;
85    }
86
87    /* Check if we deserve the token */
88    if (mm->token_priority > swap_token_mm->token_priority)
89        goto replace_token;
90
91update_priority:
92    trace_update_swap_token_priority(mm, old_prio, swap_token_mm);
93
94out:
95    mm->faultstamp = global_faults;
96    mm->last_interval = current_interval;
97    spin_unlock(&swap_token_lock);
98    return;
99
100replace_token:
101    mm->token_priority += 2;
102    trace_replace_swap_token(swap_token_mm, mm);
103    swap_token_mm = mm;
104    swap_token_memcg = swap_token_memcg_from_mm(mm);
105    last_aging = global_faults;
106    goto out;
107}
108
109/* Called on process exit. */
110void __put_swap_token(struct mm_struct *mm)
111{
112    spin_lock(&swap_token_lock);
113    if (likely(mm == swap_token_mm)) {
114        trace_put_swap_token(swap_token_mm);
115        swap_token_mm = NULL;
116        swap_token_memcg = NULL;
117    }
118    spin_unlock(&swap_token_lock);
119}
120
121static bool match_memcg(struct mem_cgroup *a, struct mem_cgroup *b)
122{
123    if (!a)
124        return true;
125    if (!b)
126        return true;
127    if (a == b)
128        return true;
129    return false;
130}
131
132void disable_swap_token(struct mem_cgroup *memcg)
133{
134    /* memcg reclaim don't disable unrelated mm token. */
135    if (match_memcg(memcg, swap_token_memcg)) {
136        spin_lock(&swap_token_lock);
137        if (match_memcg(memcg, swap_token_memcg)) {
138            trace_disable_swap_token(swap_token_mm);
139            swap_token_mm = NULL;
140            swap_token_memcg = NULL;
141        }
142        spin_unlock(&swap_token_lock);
143    }
144}
145

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