Re: [PATCH]vmscan: handle underflow for get_scan_ratio

KOSAKI Motohiro
2010-03-30T07:31:53Z

> > > > Very unfortunately, this patch isn't acceptable. In past time, vmscan
> > > > had similar logic, but 1% swap-out made lots bug reports.
> > > can you elaborate this?
> > > Completely restore previous behavior (do full scan with priority 0) is
> > > ok too.
> >
> > This is a option. but we need to know the root cause anyway.
> I thought I mentioned the root cause in first mail. My debug shows
> recent_rotated[0] is big, but recent_rotated[1] is almost zero, which makes
> percent[0] 0. But you can double check too.

To revert can save percent[0]==0 && priority==0 case. but it shouldn't
happen, I think. It mean to happen big latency issue.

Can you please try following patch? Also, I'll prepare reproduce environment soon.

---
mm/vmscan.c | 12 ++++++++----
1 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 79c8098..abf7f79 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1571,15 +1571,19 @@ static void get_scan_ratio(struct zone *zone, struct scan_control *sc,
*/
if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
spin_lock_irq(&zone->lru_lock);
- reclaim_stat->recent_scanned[0] /= 2;
- reclaim_stat->recent_rotated[0] /= 2;
+ while (reclaim_stat->recent_scanned[0] > anon / 4) {
+ reclaim_stat->recent_scanned[0] /= 2;
+ reclaim_stat->recent_rotated[0] /= 2;
+ }
spin_unlock_irq(&zone->lru_lock);
}

if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
spin_lock_irq(&zone->lru_lock);
- reclaim_stat->recent_scanned[1] /= 2;
- reclaim_stat->recent_rotated[1] /= 2;
+ while (reclaim_stat->recent_scanned[1] > file / 4) {
+ reclaim_stat->recent_scanned[1] /= 2;
+ reclaim_stat->recent_rotated[1] /= 2;
+ }
spin_unlock_irq(&zone->lru_lock);
}

--
1.6.5.2