Date: Tue, 3 Feb 2015 16:21:21 +0100
From: Michal Hocko <mhocko@suse.cz>
To: Mel Gorman <mgorman@suse.de>
Cc: Vlastimil Babka <vbabka@suse.cz>, Dave Hansen <dave.hansen@intel.com>,
        linux-mm@kvack.org, Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
        mtk.manpages@gmail.com, linux-man@vger.kernel.org
Subject: Re: MADV_DONTNEED semantics? Was: [RFC PATCH] mm: madvise: Ignore
 repeated MADV_DONTNEED hints
Message-ID: <20150203152121.GC8914@dhcp22.suse.cz>
References: <20150202165525.GM2395@suse.de>
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 <54D08483.40209@suse.cz>
 <20150203111600.GR2395@suse.de>
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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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