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.
8 * Simple token based thrashing protection, using the algorithm
9 * described in: http://www.cs.wm.edu/~sjiang/token.pdf
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.
20 #include <linux/jiffies.h>
22 #include <linux/sched.h>
23 #include <linux/swap.h>
25 static DEFINE_SPINLOCK(swap_token_lock
);
26 struct mm_struct
*swap_token_mm
;
27 static unsigned int global_faults
;
29 void grab_swap_token(struct mm_struct
*mm
)
35 current_interval
= global_faults
- mm
->faultstamp
;
37 if (!spin_trylock(&swap_token_lock
))
40 /* First come first served */
41 if (swap_token_mm
== NULL
) {
42 mm
->token_priority
= mm
->token_priority
+ 2;
47 if (mm
!= swap_token_mm
) {
48 if (current_interval
< mm
->last_interval
)
51 if (likely(mm
->token_priority
> 0))
54 /* Check if we deserve the token */
55 if (mm
->token_priority
> swap_token_mm
->token_priority
) {
56 mm
->token_priority
+= 2;
60 /* Token holder came in again! */
61 mm
->token_priority
+= 2;
65 mm
->faultstamp
= global_faults
;
66 mm
->last_interval
= current_interval
;
67 spin_unlock(&swap_token_lock
);
70 /* Called on process exit. */
71 void __put_swap_token(struct mm_struct
*mm
)
73 spin_lock(&swap_token_lock
);
74 if (likely(mm
== swap_token_mm
))
76 spin_unlock(&swap_token_lock
);
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