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[sfrench/cifs-2.6.git] / mm / thrash.c

diff --git a/mm/thrash.c b/mm/thrash.c
index f4c560b4a2b79862340fe7457af001f8e6141715..c4c5205a9c35f82c2dc34b52b4b37a8b0a0ecc44 100644 (file)
--- a/mm/thrash.c
+++ b/mm/thrash.c
@@ -7,100 +7,73 @@
  *
  * Simple token based thrashing protection, using the algorithm
  * described in:  http://www.cs.wm.edu/~sjiang/token.pdf
+ *
+ * Sep 2006, Ashwin Chaugule <ashwin.chaugule@celunite.com>
+ * Improved algorithm to pass token:
+ * Each task has a priority which is incremented if it contended
+ * for the token in an interval less than its previous attempt.
+ * If the token is acquired, that task's priority is boosted to prevent
+ * the token from bouncing around too often and to let the task make
+ * some progress in its execution.
  */
+
 #include <linux/jiffies.h>
 #include <linux/mm.h>
 #include <linux/sched.h>
 #include <linux/swap.h>
 
 static DEFINE_SPINLOCK(swap_token_lock);
-static unsigned long swap_token_timeout;
-static unsigned long swap_token_check;
-struct mm_struct * swap_token_mm = &init_mm;
-
-#define SWAP_TOKEN_CHECK_INTERVAL (HZ * 2)
-#define SWAP_TOKEN_TIMEOUT     (300 * HZ)
-/*
- * Currently disabled; Needs further code to work at HZ * 300.
- */
-unsigned long swap_token_default_timeout = SWAP_TOKEN_TIMEOUT;
-
-/*
- * Take the token away if the process had no page faults
- * in the last interval, or if it has held the token for
- * too long.
- */
-#define SWAP_TOKEN_ENOUGH_RSS 1
-#define SWAP_TOKEN_TIMED_OUT 2
-static int should_release_swap_token(struct mm_struct *mm)
-{
-       int ret = 0;
-       if (!mm->recent_pagein)
-               ret = SWAP_TOKEN_ENOUGH_RSS;
-       else if (time_after(jiffies, swap_token_timeout))
-               ret = SWAP_TOKEN_TIMED_OUT;
-       mm->recent_pagein = 0;
-       return ret;
-}
+struct mm_struct *swap_token_mm;
+static unsigned int global_faults;
 
-/*
- * Try to grab the swapout protection token.  We only try to
- * grab it once every TOKEN_CHECK_INTERVAL, both to prevent
- * SMP lock contention and to check that the process that held
- * the token before is no longer thrashing.
- */
 void grab_swap_token(void)
 {
-       struct mm_struct *mm;
-       int reason;
+       int current_interval;
 
-       /* We have the token. Let others know we still need it. */
-       if (has_swap_token(current->mm)) {
-               current->mm->recent_pagein = 1;
-               if (unlikely(!swap_token_default_timeout))
-                       disable_swap_token();
-               return;
-       }
-
-       if (time_after(jiffies, swap_token_check)) {
+       global_faults++;
 
-               if (!swap_token_default_timeout) {
-                       swap_token_check = jiffies + SWAP_TOKEN_CHECK_INTERVAL;
-                       return;
-               }
-
-               /* ... or if we recently held the token. */
-               if (time_before(jiffies, current->mm->swap_token_time))
-                       return;
+       current_interval = global_faults - current->mm->faultstamp;
 
-               if (!spin_trylock(&swap_token_lock))
-                       return;
+       if (!spin_trylock(&swap_token_lock))
+               return;
 
-               swap_token_check = jiffies + SWAP_TOKEN_CHECK_INTERVAL;
+       /* First come first served */
+       if (swap_token_mm == NULL) {
+               current->mm->token_priority = current->mm->token_priority + 2;
+               swap_token_mm = current->mm;
+               goto out;
+       }
 
-               mm = swap_token_mm;
-               if ((reason = should_release_swap_token(mm))) {
-                       unsigned long eligible = jiffies;
-                       if (reason == SWAP_TOKEN_TIMED_OUT) {
-                               eligible += swap_token_default_timeout;
-                       }
-                       mm->swap_token_time = eligible;
-                       swap_token_timeout = jiffies + swap_token_default_timeout;
+       if (current->mm != swap_token_mm) {
+               if (current_interval < current->mm->last_interval)
+                       current->mm->token_priority++;
+               else {
+                       if (likely(current->mm->token_priority > 0))
+                               current->mm->token_priority--;
+               }
+               /* Check if we deserve the token */
+               if (current->mm->token_priority >
+                               swap_token_mm->token_priority) {
+                       current->mm->token_priority += 2;
                        swap_token_mm = current->mm;
                }
-               spin_unlock(&swap_token_lock);
+       } else {
+               /* Token holder came in again! */
+               current->mm->token_priority += 2;
        }
-       return;
+
+out:
+       current->mm->faultstamp = global_faults;
+       current->mm->last_interval = current_interval;
+       spin_unlock(&swap_token_lock);
+return;
 }
 
 /* Called on process exit. */
 void __put_swap_token(struct mm_struct *mm)
 {
        spin_lock(&swap_token_lock);
-       if (likely(mm == swap_token_mm)) {
-               mm->swap_token_time = jiffies + SWAP_TOKEN_CHECK_INTERVAL;
-               swap_token_mm = &init_mm;
-               swap_token_check = jiffies;
-       }
+       if (likely(mm == swap_token_mm))
+               swap_token_mm = NULL;
        spin_unlock(&swap_token_lock);
 }