linux-kernel - Re: MADV_DONTNEED semantics? Was: [RFC PATCH] mm: madvise: Ignore repeated MADV

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Message-ID: <20150203152121.GC8914@dhcp22.suse.cz>
Date:	Tue, 3 Feb 2015 16:21:21 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Vlastimil Babka <vbabka@...e.cz>,
	Dave Hansen <dave.hansen@...el.com>, linux-mm@...ck.org,
	Minchan Kim <minchan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	mtk.manpages@...il.com, linux-man@...r.kernel.org
Subject: Re: MADV_DONTNEED semantics? Was: [RFC PATCH] mm: madvise: Ignore
 repeated MADV_DONTNEED hints

On Tue 03-02-15 11:16:00, Mel Gorman wrote:
> On Tue, Feb 03, 2015 at 09:19:15AM +0100, Vlastimil Babka wrote:
[...]
> > And if we agree that there is indeed no guarantee, what's the actual semantic
> > difference from MADV_FREE? I guess none? So there's only a possible perfomance
> > difference?
> > 
> 
> Timing. MADV_DONTNEED if it has an effect is immediate, is a heavier
> operations and RSS is reduced. MADV_FREE only has an impact in the future
> if there is memory pressure.

JFTR. the man page for MADV_FREE has been proposed already
(https://lkml.org/lkml/2014/12/5/63 should be the last version AFAIR). I
do not see it in the man-pages git tree but the patch was not in time
for 3.19 so I guess it will only appear in 3.20.
-- 
Michal Hocko
SUSE Labs
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