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Following bug was uncovered by compiling with '-W' flag: CC mm/thrash.o mm/thrash.c: In function âgrab_swap_tokenâ: mm/thrash.c:52: warning: comparison of unsigned expression < 0 is always false Variable token_priority is unsigned, so decrementing first and then checking the result does not work; fixed by reversing the test, patch attached (compile tested only). I am not sure if likely() makes much sense in this new situation, but I'll let somebody else to make a decision on that. Signed-off-by: Mika Kukkonen <mikukkon@iki.fi> Cc: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
80 lines
2.0 KiB
C
80 lines
2.0 KiB
C
/*
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* mm/thrash.c
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*
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* Copyright (C) 2004, Red Hat, Inc.
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* Copyright (C) 2004, Rik van Riel <riel@redhat.com>
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* Released under the GPL, see the file COPYING for details.
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*
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* Simple token based thrashing protection, using the algorithm
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* described in: http://www.cs.wm.edu/~sjiang/token.pdf
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*
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* Sep 2006, Ashwin Chaugule <ashwin.chaugule@celunite.com>
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* Improved algorithm to pass token:
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* Each task has a priority which is incremented if it contended
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* for the token in an interval less than its previous attempt.
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* If the token is acquired, that task's priority is boosted to prevent
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* the token from bouncing around too often and to let the task make
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* some progress in its execution.
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*/
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#include <linux/jiffies.h>
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#include <linux/mm.h>
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#include <linux/sched.h>
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#include <linux/swap.h>
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static DEFINE_SPINLOCK(swap_token_lock);
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struct mm_struct *swap_token_mm;
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static unsigned int global_faults;
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void grab_swap_token(void)
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{
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int current_interval;
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global_faults++;
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current_interval = global_faults - current->mm->faultstamp;
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if (!spin_trylock(&swap_token_lock))
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return;
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/* First come first served */
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if (swap_token_mm == NULL) {
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current->mm->token_priority = current->mm->token_priority + 2;
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swap_token_mm = current->mm;
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goto out;
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}
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if (current->mm != swap_token_mm) {
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if (current_interval < current->mm->last_interval)
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current->mm->token_priority++;
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else {
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if (likely(current->mm->token_priority > 0))
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current->mm->token_priority--;
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}
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/* Check if we deserve the token */
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if (current->mm->token_priority >
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swap_token_mm->token_priority) {
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current->mm->token_priority += 2;
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swap_token_mm = current->mm;
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}
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} else {
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/* Token holder came in again! */
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current->mm->token_priority += 2;
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}
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out:
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current->mm->faultstamp = global_faults;
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current->mm->last_interval = current_interval;
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spin_unlock(&swap_token_lock);
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return;
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}
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/* Called on process exit. */
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void __put_swap_token(struct mm_struct *mm)
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{
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spin_lock(&swap_token_lock);
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if (likely(mm == swap_token_mm))
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swap_token_mm = NULL;
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spin_unlock(&swap_token_lock);
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}
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