linux-kernel - Re: [PATCH] vmscan: do not evict inactive pages when skipping an active list scan

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Message-Id: <20091126110340.5A62.A69D9226@jp.fujitsu.com>
Date:	Thu, 26 Nov 2009 11:50:17 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	kosaki.motohiro@...fujitsu.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, lwoodman@...hat.com,
	kosaki.motohiro@...itsu.co.jp,
	Tomasz Chmielewski <mangoo@...g.org>, akpm@...ux-foundation.org
Subject: Re: [PATCH] vmscan: do not evict inactive pages when skipping an active list scan

> In AIM7 runs, recent kernels start swapping out anonymous pages
> well before they should.  This is due to shrink_list falling
> through to shrink_inactive_list if !inactive_anon_is_low(zone, sc),
> when all we really wanted to do is pre-age some anonymous pages to
> give them extra time to be referenced while on the inactive list.
> 
> The obvious fix is to make sure that shrink_list does not fall
> through to scanning/reclaiming inactive pages when we called it
> to scan one of the active lists.
> 
> This change should be safe because the loop in shrink_zone ensures
> that we will still shrink the anon and file inactive lists whenever
> we should.

Good catch!


> 
> Reported-by: Larry Woodman <lwoodman@...hat.com>
> Signed-off-by: Rik van Riel <riel@...hat.com>
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 777af57..ec4dfda 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1469,13 +1469,15 @@ static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
>  {
>  	int file = is_file_lru(lru);
>  
> -	if (lru == LRU_ACTIVE_FILE && inactive_file_is_low(zone, sc)) {
> -		shrink_active_list(nr_to_scan, zone, sc, priority, file);
> +	if (lru == LRU_ACTIVE_FILE) {
> +		if (inactive_file_is_low(zone, sc))
> +		      shrink_active_list(nr_to_scan, zone, sc, priority, file);
>  		return 0;
>  	}
>  
> -	if (lru == LRU_ACTIVE_ANON && inactive_anon_is_low(zone, sc)) {
> -		shrink_active_list(nr_to_scan, zone, sc, priority, file);
> +	if (lru == LRU_ACTIVE_ANON) {
> +		if (inactive_file_is_low(zone, sc))

This inactive_file_is_low() should be inactive_anon_is_low().
cut-n-paste programming often makes similar mistake. probaby we need make
more cleanup to this function.

How about this? (this is incremental patch from you)


Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
---
 mm/vmscan.c |   17 ++++++++++-------
 1 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index a8f61c0..80e94a2 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1467,22 +1467,25 @@ static int inactive_file_is_low(struct zone *zone, struct scan_control *sc)
 	return low;
 }
 
+static int inactive_list_is_low(struct zone *zone, struct scan_control *sc, int file)
+{
+	if (file)
+		return inactive_file_is_low(zone, sc);
+	else
+		return inactive_anon_is_low(zone, sc);
+}
+
 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
 	struct zone *zone, struct scan_control *sc, int priority)
 {
 	int file = is_file_lru(lru);
 
-	if (lru == LRU_ACTIVE_FILE) {
-		if (inactive_file_is_low(zone, sc))
+	if (is_active_lru(lru)) {
+		if (inactive_list_is_low(zone, sc, file))
 		      shrink_active_list(nr_to_scan, zone, sc, priority, file);
 		return 0;
 	}
 
-	if (lru == LRU_ACTIVE_ANON) {
-		if (inactive_file_is_low(zone, sc))
-		      shrink_active_list(nr_to_scan, zone, sc, priority, file);
-		return 0;
-	}
 	return shrink_inactive_list(nr_to_scan, zone, sc, priority, file);
 }
 
-- 
1.6.5.2






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