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.cse.ohio-state.edu/hpcs/WWW/HTML/publications/abs05-1.html
  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
  30 static DEFINE_SPINLOCK(swap_token_lock);
  31 struct mm_struct *swap_token_mm;
  32 static struct mem_cgroup *swap_token_memcg;
  33
  34 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
  35 static struct mem_cgroup *swap_token_memcg_from_mm(struct mm_struct *mm)
  36 {
  37         struct mem_cgroup *memcg;
  38
  39         memcg = try_get_mem_cgroup_from_mm(mm);
  40         if (memcg)
  41                 css_put(mem_cgroup_css(memcg));
  42
  43         return memcg;
  44 }
  45 #else
  46 static struct mem_cgroup *swap_token_memcg_from_mm(struct mm_struct *mm)
  47 {
  48         return NULL;
  49 }
  50 #endif
  51
  52 void grab_swap_token(struct mm_struct *mm)
  53 {
  54         int current_interval;
  55         unsigned int old_prio = mm->token_priority;
  56         static unsigned int global_faults;
  57         static unsigned int last_aging;
  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         /*
  71          * Usually, we don't need priority aging because long interval faults
  72          * makes priority decrease quickly. But there is one exception. If the
  73          * token owner task is sleeping, it never make long interval faults.
  74          * Thus, we need a priority aging mechanism instead. The requirements
  75          * of priority aging are
  76          *  1) An aging interval is reasonable enough long. Too short aging
  77          *     interval makes quick swap token lost and decrease performance.
  78          *  2) The swap token owner task have to get priority aging even if
  79          *     it's under sleep.
  80          */
  81         if ((global_faults - last_aging) > TOKEN_AGING_INTERVAL) {
  82                 swap_token_mm->token_priority /= 2;
  83                 last_aging = global_faults;
  84         }
  85
  86         if (mm == swap_token_mm) {
  87                 mm->token_priority += 2;
  88                 goto update_priority;
  89         }
  90
  91         if (current_interval < mm->last_interval)
  92                 mm->token_priority++;
  93         else {
  94                 if (likely(mm->token_priority > 0))
  95                         mm->token_priority--;
  96         }
  97
  98         /* Check if we deserve the token */
  99         if (mm->token_priority > swap_token_mm->token_priority)
 100                 goto replace_token;
 101
 102 update_priority:
 103         trace_update_swap_token_priority(mm, old_prio, swap_token_mm);
 104
 105 out:
 106         mm->faultstamp = global_faults;
 107         mm->last_interval = current_interval;
 108         spin_unlock(&swap_token_lock);
 109         return;
 110
 111 replace_token:
 112         mm->token_priority += 2;
 113         trace_replace_swap_token(swap_token_mm, mm);
 114         swap_token_mm = mm;
 115         swap_token_memcg = swap_token_memcg_from_mm(mm);
 116         last_aging = global_faults;
 117         goto out;
 118 }
 119
 120 /* Called on process exit. */
 121 void __put_swap_token(struct mm_struct *mm)
 122 {
 123         spin_lock(&swap_token_lock);
 124         if (likely(mm == swap_token_mm)) {
 125                 trace_put_swap_token(swap_token_mm);
 126                 swap_token_mm = NULL;
 127                 swap_token_memcg = NULL;
 128         }
 129         spin_unlock(&swap_token_lock);
 130 }
 131
 132 static bool match_memcg(struct mem_cgroup *a, struct mem_cgroup *b)
 133 {
 134         if (!a)
 135                 return true;
 136         if (!b)
 137                 return true;
 138         if (a == b)
 139                 return true;
 140         return false;
 141 }
 142
 143 void disable_swap_token(struct mem_cgroup *memcg)
 144 {
 145         /* memcg reclaim don't disable unrelated mm token. */
 146         if (match_memcg(memcg, swap_token_memcg)) {
 147                 spin_lock(&swap_token_lock);
 148                 if (match_memcg(memcg, swap_token_memcg)) {
 149                         trace_disable_swap_token(swap_token_mm);
 150                         swap_token_mm = NULL;
 151                         swap_token_memcg = NULL;
 152                 }
 153                 spin_unlock(&swap_token_lock);
 154         }
 155 }