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SubjectRe: [PATCH] mm: compaction: Abort compaction if too many pages are isolated and caller is asynchronous
On Fri, Jun 03, 2011 at 05:45:54PM +0200, Andrea Arcangeli wrote:
> 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>

Well spotted.

Acked-by: Mel Gorman <mgorman@suse.de>

Minor nit. swapper_space is rarely referred to outside of the swap
code. Might it be more readable to use

/*
* swapcache is accounted as NR_FILE_PAGES but it is not
* accounted as NR_SHMEM
*
if (PageSwapBacked(page) && !PageSwapCache(page))
?

> ---
>
> 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);
> }
>
>

--
Mel Gorman
SUSE Labs


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