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
  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 }