LXR linux/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
  25static DEFINE_SPINLOCK(swap_token_lock);
  26struct mm_struct *swap_token_mm;
  27static unsigned int global_faults;
  28
  29void grab_swap_token(void)
  30{
  31        int current_interval;
  32
  33        global_faults++;
  34
  35        current_interval = global_faults - current->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                current->mm->token_priority = current->mm->token_priority + 2;
  43                swap_token_mm = current->mm;
  44                goto out;
  45        }
  46
  47        if (current->mm != swap_token_mm) {
  48                if (current_interval < current->mm->last_interval)
  49                        current->mm->token_priority++;
  50                else {
  51                        if (likely(current->mm->token_priority > 0))
  52                                current->mm->token_priority--;
  53                }
  54                /* Check if we deserve the token */
  55                if (current->mm->token_priority >
  56                                swap_token_mm->token_priority) {
  57                        current->mm->token_priority += 2;
  58                        swap_token_mm = current->mm;
  59                }
  60        } else {
  61                /* Token holder came in again! */
  62                current->mm->token_priority += 2;
  63        }
  64
  65out:
  66        current->mm->faultstamp = global_faults;
  67        current->mm->last_interval = current_interval;
  68        spin_unlock(&swap_token_lock);
  69return;
  70}
  71
  72/* Called on process exit. */
  73void __put_swap_token(struct mm_struct *mm)
  74{
  75        spin_lock(&swap_token_lock);
  76        if (likely(mm == swap_token_mm))
  77                swap_token_mm = NULL;
  78        spin_unlock(&swap_token_lock);
  79}
  80