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

[Andrea Arcangeli <aarcange@redhat.com>]

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@redhat.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@redhat.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);
 	}