mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-30 08:04:13 +08:00
7faaa5f0bf
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
/*
|
|
* 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(void)
|
|
{
|
|
int current_interval;
|
|
|
|
global_faults++;
|
|
|
|
current_interval = global_faults - current->mm->faultstamp;
|
|
|
|
if (!spin_trylock(&swap_token_lock))
|
|
return;
|
|
|
|
/* First come first served */
|
|
if (swap_token_mm == NULL) {
|
|
current->mm->token_priority = current->mm->token_priority + 2;
|
|
swap_token_mm = current->mm;
|
|
goto out;
|
|
}
|
|
|
|
if (current->mm != swap_token_mm) {
|
|
if (current_interval < current->mm->last_interval)
|
|
current->mm->token_priority++;
|
|
else {
|
|
if (likely(current->mm->token_priority > 0))
|
|
current->mm->token_priority--;
|
|
}
|
|
/* Check if we deserve the token */
|
|
if (current->mm->token_priority >
|
|
swap_token_mm->token_priority) {
|
|
current->mm->token_priority += 2;
|
|
swap_token_mm = current->mm;
|
|
}
|
|
} else {
|
|
/* Token holder came in again! */
|
|
current->mm->token_priority += 2;
|
|
}
|
|
|
|
out:
|
|
current->mm->faultstamp = global_faults;
|
|
current->mm->last_interval = current_interval;
|
|
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))
|
|
swap_token_mm = NULL;
|
|
spin_unlock(&swap_token_lock);
|
|
}
|