linux-kernel - Re: [PATCH]vmscan: handle underflow for get_scan

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Message-Id: <20100330160820.8EA8.A69D9226@jp.fujitsu.com>
Date:	Tue, 30 Mar 2010 16:31:40 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"Wu, Fengguang" <fengguang.wu@...el.com>
Subject: Re: [PATCH]vmscan: handle underflow for get_scan_ratio

> > > > 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





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