Message-ID: <51483B12.6040502@gmail.com>
Date: Tue, 19 Mar 2013 18:16:50 +0800
From: Simon Jeons <simon.jeons@gmail.com>
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To: Mel Gorman <mgorman@suse.de>
CC: Linux-MM <linux-mm@kvack.org>, Jiri Slaby <jslaby@suse.cz>,
        Valdis Kletnieks <Valdis.Kletnieks@vt.edu>,
        Rik van Riel <riel@redhat.com>, Zlatko Calusic <zcalusic@bitsync.net>,
        Johannes Weiner <hannes@cmpxchg.org>, dormando <dormando@rydia.net>,
        Satoru Moriya <satoru.moriya@hds.com>, Michal Hocko <mhocko@suse.cz>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 01/10] mm: vmscan: Limit the number of pages kswapd reclaims
 at each priority
References: <1363525456-10448-1-git-send-email-mgorman@suse.de> <1363525456-10448-2-git-send-email-mgorman@suse.de> <5147A8EC.5010908@gmail.com> <20130319095514.GA2055@suse.de>
In-Reply-To: <20130319095514.GA2055@suse.de>
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Hi Mel,
On 03/19/2013 05:55 PM, Mel Gorman wrote:
> On Tue, Mar 19, 2013 at 07:53:16AM +0800, Simon Jeons wrote:
>> Hi Mel,
>> On 03/17/2013 09:04 PM, 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
>> Since there is nr_reclaimed >= nr_to_reclaim check if priority is
>> large than DEF_PRIORITY in shrink_lruvec, how can a large percentage
>> of memory is suddenly freed happen?
>>
> Because of the priority checks made in get_scan_count(). Patch 5 has
> more detail on why this happens.
>
But nr_reclaim >= nr_to_reclaim check in function shrink_lruvec is after 
scan each evictable lru, so if priority == 0, still scan the whole world.
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