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/*
* 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
*/
#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;
}
/*
* 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;
/* 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)) {
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;
if (!spin_trylock(&swap_token_lock))
return;
swap_token_check = jiffies + SWAP_TOKEN_CHECK_INTERVAL;
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;
swap_token_mm = current->mm;
}
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;
}
spin_unlock(&swap_token_lock);
}
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