Re: [PATCH]vmscan: handle underflow for get_scan_ratio

KOSAKI Motohiro
2010-04-02T09:13:14Z

> > Yeah, I don't want ignore .33-stable too. if I can't find the root cause
> > in 2-3 days, I'll revert guilty patch anyway.
> >
>
> It's a good idea to avoid fixing a bug one-way-in-stable,
> other-way-in-mainline. Because then we have new code in both trees
> which is different. And the -stable guys sensibly like to see code get
> a bit of a shakedown in mainline before backporting it.
>
> So it would be better to merge the "simple" patch into mainline, tagged
> for -stable backporting. Then we can later implement the larger fix in
> mainline, perhaps starting by reverting the "simple" fix.

.....ok. I don't have to prevent your code maintainship. although I still
think we need to fix the issue completely.

===================================================================
>From 52358cbccdfe94e0381974cd6e937bcc6b1c608b Mon Sep 17 00:00:00 2001
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Date: Fri, 2 Apr 2010 17:13:48 +0900
Subject: [PATCH] Revert "vmscan: get_scan_ratio() cleanup"

Shaohua Li reported his tmpfs streaming I/O test can lead to make oom.
The test uses a 6G tmpfs in a system with 3G memory. In the tmpfs,
there are 6 copies of kernel source and the test does kbuild for each
copy. His investigation shows the test has a lot of rotated anon
pages and quite few file pages, so get_scan_ratio calculates percent[0]
(i.e. scanning percent for anon) to be zero. Actually the percent[0]
shoule be a big value, but our calculation round it to zero.

Although before commit 84b18490, we have the same sick too. but the old
logic can rescue percent[0]==0 case only when priority==0. It had hided
the real issue. I didn't think merely streaming io can makes percent[0]==0
&& priority==0 situation. but I was wrong.

So, definitely we have to fix such tmpfs streaming io issue. but anyway
I revert the regression commit at first.

This reverts commit 84b18490d1f1bc7ed5095c929f78bc002eb70f26.

Reported-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
---
mm/vmscan.c | 23 +++++++++--------------
1 files changed, 9 insertions(+), 14 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 79c8098..cb3947e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1535,13 +1535,6 @@ static void get_scan_ratio(struct zone *zone, struct scan_control *sc,
unsigned long ap, fp;
struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);

- /* If we have no swap space, do not bother scanning anon pages. */
- if (!sc->may_swap || (nr_swap_pages <= 0)) {
- percent[0] = 0;
- percent[1] = 100;
- return;
- }
-
anon = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
file = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
@@ -1639,20 +1632,22 @@ static void shrink_zone(int priority, struct zone *zone,
unsigned long nr_reclaimed = sc->nr_reclaimed;
unsigned long nr_to_reclaim = sc->nr_to_reclaim;
struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
+ int noswap = 0;

- get_scan_ratio(zone, sc, percent);
+ /* If we have no swap space, do not bother scanning anon pages. */
+ if (!sc->may_swap || (nr_swap_pages <= 0)) {
+ noswap = 1;
+ percent[0] = 0;
+ percent[1] = 100;
+ } else
+ get_scan_ratio(zone, sc, percent);

for_each_evictable_lru(l) {
int file = is_file_lru(l);
unsigned long scan;

- if (percent[file] == 0) {
- nr[l] = 0;
- continue;
- }
-
scan = zone_nr_lru_pages(zone, sc, l);
- if (priority) {
+ if (priority || noswap) {
scan >>= priority;
scan = (scan * percent[file]) / 100;
}
--
1.6.5.2