linux-kernel - Re: [PATCH RFC 1/4] mm: throttle MADV

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Message-ID: <20150225141337.GE26680@dhcp22.suse.cz>
Date:	Wed, 25 Feb 2015 15:13:37 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Shaohua Li <shli@...nel.org>
Cc:	Minchan Kim <minchan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mgorman@...e.de>, Yalin.Wang@...ymobile.com
Subject: Re: [PATCH RFC 1/4] mm: throttle MADV_FREE

On Tue 24-02-15 14:54:01, Shaohua Li wrote:
> On Tue, Feb 24, 2015 at 04:43:18PM +0100, Michal Hocko wrote:
> > On Tue 24-02-15 17:18:14, Minchan Kim wrote:
> > > Recently, Shaohua reported that MADV_FREE is much slower than
> > > MADV_DONTNEED in his MADV_FREE bomb test. The reason is many of
> > > applications went to stall with direct reclaim since kswapd's
> > > reclaim speed isn't fast than applications's allocation speed
> > > so that it causes lots of stall and lock contention.
> > 
> > I am not sure I understand this correctly. So the issue is that there is
> > huge number of MADV_FREE on the LRU and they are not close to the tail
> > of the list so the reclaim has to do a lot of work before it starts
> > dropping them?
> 
> I thought the main reason is current reclaim stragety. Anonymous pages are
> considered to be hard to be reclaimed with current policy, VM bias to reclaim
> file pages (anon pages are in active list first, referenced pte will reactivate
> anon pages and increase rotate count)

Makes sense. We are really biasing to page cache reclaim most of the
time.

-- 
Michal Hocko
SUSE Labs
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