linux-kernel - Re: [PATCH 06/10] vmscan: Narrow the scenarios lumpy reclaim uses synchrounous reclaim

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Date:	Thu, 9 Sep 2010 12:14:15 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	Linux Kernel List <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	Christoph Hellwig <hch@....de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 06/10] vmscan: Narrow the scenarios lumpy reclaim uses
 synchrounous reclaim

On Mon,  6 Sep 2010 11:47:29 +0100
Mel Gorman <mel@....ul.ie> wrote:

> From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> 
> shrink_page_list() can decide to give up reclaiming a page under a
> number of conditions such as
> 
>   1. trylock_page() failure
>   2. page is unevictable
>   3. zone reclaim and page is mapped
>   4. PageWriteback() is true
>   5. page is swapbacked and swap is full
>   6. add_to_swap() failure
>   7. page is dirty and gfpmask don't have GFP_IO, GFP_FS
>   8. page is pinned
>   9. IO queue is congested
>  10. pageout() start IO, but not finished
> 
> When lumpy reclaim, all of failure result in entering synchronous lumpy
> reclaim but this can be unnecessary.  In cases (2), (3), (5), (6), (7) and
> (8), there is no point retrying.  This patch causes lumpy reclaim to abort
> when it is known it will fail.
> 
> Case (9) is more interesting. current behavior is,
>   1. start shrink_page_list(async)
>   2. found queue_congested()
>   3. skip pageout write
>   4. still start shrink_page_list(sync)
>   5. wait on a lot of pages
>   6. again, found queue_congested()
>   7. give up pageout write again
> 
> So, it's meaningless time wasting. However, just skipping page reclaim is
> also not a good as as x86 allocating a huge page needs 512 pages for example.
> It can have more dirty pages than queue congestion threshold (~=128).
> 
> After this patch, pageout() behaves as follows;
> 
>  - If order > PAGE_ALLOC_COSTLY_ORDER
> 	Ignore queue congestion always.
>  - If order <= PAGE_ALLOC_COSTLY_ORDER
> 	skip write page and disable lumpy reclaim.
> 
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Signed-off-by: Mel Gorman <mel@....ul.ie>

seems nice.
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>


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