linux-kernel - Re: [PATCH 03/10] mm: vmscan: Flatten kswapd priority loop

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Message-ID: <20130319082330.GA7869@dhcp22.suse.cz>
Date:	Tue, 19 Mar 2013 09:23:30 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Simon Jeons <simon.jeons@...il.com>
Cc:	Mel Gorman <mgorman@...e.de>, Linux-MM <linux-mm@...ck.org>,
	Jiri Slaby <jslaby@...e.cz>,
	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 03/10] mm: vmscan: Flatten kswapd priority loop

On Tue 19-03-13 11:08:23, Simon Jeons wrote:
> Hi Mel,
> On 03/17/2013 09:04 PM, Mel Gorman wrote:
> >kswapd stops raising the scanning priority when at least SWAP_CLUSTER_MAX
> >pages have been reclaimed or the pgdat is considered balanced. It then
> >rechecks if it needs to restart at DEF_PRIORITY and whether high-order
> >reclaim needs to be reset. This is not wrong per-se but it is confusing
> 
> per-se is short for what?
> 
> >to follow and forcing kswapd to stay at DEF_PRIORITY may require several
> >restarts before it has scanned enough pages to meet the high watermark even
> >at 100% efficiency. This patch irons out the logic a bit by controlling
> >when priority is raised and removing the "goto loop_again".
> >
> >This patch has kswapd raise the scanning priority until it is scanningmm: vmscan: Flatten kswapd priority loop
> >enough pages that it could meet the high watermark in one shrink of the
> >LRU lists if it is able to reclaim at 100% efficiency. It will not raise
> 
> Which kind of reclaim can be treated as 100% efficiency?

nr_scanned == nr_reclaimed
 
> >the scanning prioirty higher unless it is failing to reclaim any pages.
> >
> >To avoid infinite looping for high-order allocation requests kswapd will
> >not reclaim for high-order allocations when it has reclaimed at least
> >twice the number of pages as the allocation request.
> >
> >Signed-off-by: Mel Gorman <mgorman@...e.de>
[...]
-- 
Michal Hocko
SUSE Labs
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