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The new swap token patches replace the current token traversal algo. The old algo had a crude timeout parameter that was used to handover the token from one task to another. This algo, transfers the token to the tasks that are in need of the token. The urgency for the token is based on the number of times a task is required to swap-in pages. Accordingly, the priority of a task is incremented if it has been badly affected due to swap-outs. To ensure that the token doesnt bounce around rapidly, the token holders are given a priority boost. The priority of tasks is also decremented, if their rate of swap-in's keeps reducing. This way, the condition to check whether to pre-empt the swap token, is a matter of comparing two task's priority fields. [akpm@osdl.org: cleanups] Signed-off-by: Ashwin Chaugule <ashwin.chaugule@celunite.com> Cc: Rik van Riel <riel@redhat.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
81 lines
2.1 KiB
C
81 lines
2.1 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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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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current->mm->token_priority--;
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if (unlikely(current->mm->token_priority < 0))
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current->mm->token_priority = 0;
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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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