linux-kernel - Re: [PATCH 01/10] mm: vmscan: Limit the number of pages kswapd reclaims at each priority

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Date:	Mon, 25 Mar 2013 10:13:41 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	Michal Hocko <mhocko@...e.cz>, Mel Gorman <mgorman@...e.de>
CC:	Linux-MM <linux-mm@...ck.org>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Rik van Riel <riel@...hat.com>,
	Zlatko Calusic <zcalusic@...sync.net>,
	Johannes Weiner <hannes@...xchg.org>,
	dormando <dormando@...ia.net>,
	Satoru Moriya <satoru.moriya@....com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/10] mm: vmscan: Limit the number of pages kswapd reclaims
 at each priority

On 03/25/2013 10:07 AM, Michal Hocko wrote:
> On Sun 17-03-13 13:04:07, Mel Gorman wrote:
>> The number of pages kswapd can reclaim is bound by the number of pages it
>> scans which is related to the size of the zone and the scanning priority. In
>> many cases the priority remains low because it's reset every SWAP_CLUSTER_MAX
>> reclaimed pages but in the event kswapd scans a large number of pages it
>> cannot reclaim, it will raise the priority and potentially discard a large
>> percentage of the zone as sc->nr_to_reclaim is ULONG_MAX. The user-visible
>> effect is a reclaim "spike" where a large percentage of memory is suddenly
>> freed. It would be bad enough if this was just unused memory but because
>> of how anon/file pages are balanced it is possible that applications get
>> pushed to swap unnecessarily.
>>
>> This patch limits the number of pages kswapd will reclaim to the high
>> watermark. Reclaim will will overshoot due to it not being a hard limit as
>> shrink_lruvec() will ignore the sc.nr_to_reclaim at DEF_PRIORITY but it
>> prevents kswapd reclaiming the world at higher priorities. The number of
>> pages it reclaims is not adjusted for high-order allocations as kswapd will
>> reclaim excessively if it is to balance zones for high-order allocations.
>>
>> Signed-off-by: Mel Gorman <mgorman@...e.de>
> 
> It seems I forgot to add
> Reviewed-by: Michal Hocko <mhocko@...e.cz>

Thanks, now I applied all ten.

BTW I very pray this will fix also the issue I have when I run ltp tests
(highly I/O intensive, esp. `growfiles') in a VM while playing a movie
on the host resulting in a stuttered playback ;).

-- 
js
suse labs
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