[net-next-2.6.git] / mm / thrash.c

/*
 * mm/thrash.c
 *
 * Copyright (C) 2004, Red Hat, Inc.
 * Copyright (C) 2004, Rik van Riel <riel@redhat.com>
 * Released under the GPL, see the file COPYING for details.
 *
 * 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);
struct mm_struct *swap_token_mm;
static unsigned int global_faults;

void grab_swap_token(struct mm_struct *mm)
{
	int current_interval;

	global_faults++;

	current_interval = global_faults - mm->faultstamp;

	if (!spin_trylock(&swap_token_lock))
		return;

	/* First come first served */
	if (swap_token_mm == NULL) {
		mm->token_priority = mm->token_priority + 2;
		swap_token_mm = mm;
		goto out;
	}

	if (mm != swap_token_mm) {
		if (current_interval < mm->last_interval)
			mm->token_priority++;
		else {
			if (likely(mm->token_priority > 0))
				mm->token_priority--;
		}
		/* Check if we deserve the token */
		if (mm->token_priority > swap_token_mm->token_priority) {
			mm->token_priority += 2;
			swap_token_mm = mm;
		}
	} else {
		/* Token holder came in again! */
		mm->token_priority += 2;
	}

out:
	mm->faultstamp = global_faults;
	mm->last_interval = current_interval;
	spin_unlock(&swap_token_lock);
}

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