linux-kernel - Re: [PATCH] mm: compaction: Abort compaction if too many pages are isolated and caller is asynchronous

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Date:	Fri, 3 Jun 2011 17:45:54 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Minchan Kim <minchan.kim@...il.com>, akpm@...ux-foundation.org,
	Ury Stankevich <urykhy@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, stable@...nel.org
Subject: Re: [PATCH] mm: compaction: Abort compaction if too many pages are
 isolated and caller is asynchronous

On Fri, Jun 03, 2011 at 03:49:41PM +0100, Mel Gorman wrote:
> Right idea of the wrong zone being accounted for but wrong place. I
> think the following patch should fix the problem;

Looks good thanks.

I also found this bug during my debugging that made NR_SHMEM underflow.

===
Subject: migrate: don't account swapcache as shmem

From: Andrea Arcangeli <aarcange@...hat.com>

swapcache will reach the below code path in migrate_page_move_mapping,
and swapcache is accounted as NR_FILE_PAGES but it's not accounted as
NR_SHMEM.

Signed-off-by: Andrea Arcangeli <aarcange@...hat.com>
---

diff --git a/mm/migrate.c b/mm/migrate.c
index e4a5c91..2597a27 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -288,7 +288,7 @@ static int migrate_page_move_mapping(struct address_space *mapping,
 	 */
 	__dec_zone_page_state(page, NR_FILE_PAGES);
 	__inc_zone_page_state(newpage, NR_FILE_PAGES);
-	if (PageSwapBacked(page)) {
+	if (mapping != &swapper_space && PageSwapBacked(page)) {
 		__dec_zone_page_state(page, NR_SHMEM);
 		__inc_zone_page_state(newpage, NR_SHMEM);
 	}


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