linux-kernel - Re: [PATCH 1/5] mm: compaction: Allow compaction to isolate dirty pages

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Date:	Fri, 18 Nov 2011 18:28:25 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linux-MM <linux-mm@...ck.org>, Minchan Kim <minchan.kim@...il.com>,
	Jan Kara <jack@...e.cz>, Andy Isaacson <adi@...apodia.org>,
	Johannes Weiner <jweiner@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/5] mm: compaction: Allow compaction to isolate dirty
 pages

On Fri, Nov 18, 2011 at 04:58:40PM +0000, Mel Gorman wrote:
> Commit [39deaf85: mm: compaction: make isolate_lru_page() filter-aware]
> noted that compaction does not migrate dirty or writeback pages and
> that is was meaningless to pick the page and re-add it to the LRU list.
> 
> What was missed during review is that asynchronous migration moves
> dirty pages if their ->migratepage callback is migrate_page() because
> these can be moved without blocking. This potentially impacted
> hugepage allocation success rates by a factor depending on how many
> dirty pages are in the system.
> 
> This patch partially reverts 39deaf85 to allow migration to isolate
> dirty pages again. This increases how much compaction disrupts the
> LRU but that is addressed later in the series.
> 
> Signed-off-by: Mel Gorman <mgorman@...e.de>
> ---
>  mm/compaction.c |    3 ---
>  1 files changed, 0 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 899d956..237560e 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -349,9 +349,6 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
>  			continue;
>  		}
>  
> -		if (!cc->sync)
> -			mode |= ISOLATE_CLEAN;
> -
>  		/* Try isolate the page */
>  		if (__isolate_lru_page(page, mode, 0) != 0)
>  			continue;

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