linux-kernel - Re: Memory overcommit

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Message-ID: <4AEB0291.4080003@gmail.com>
Date:	Fri, 30 Oct 2009 16:13:21 +0100
From:	Vedran Furač <vedran.furac@...il.com>
To:	tfjellstrom@...w.ca
CC:	linux-kernel@...r.kernel.org, David Rientjes <rientjes@...gle.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	minchan.kim@...il.com, Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: Memory overcommit

Thomas Fjellstrom wrote:

>> malloc: Cannot allocate memory /* Great, no OOM, but: */
>> 
>> % free -m total       used       free     shared    buffers cached
>> Mem:      3458        3429         29          0        102 1119
>> -/+ buffers/cache:    2207       1251
>> 
>> There's plenty of memory available. Shouldn't cache be 
>> automatically dropped (this question was in my original mail, hence
>>  the subject)?
>> 
> 
> I think this is the MOST serious issue related to the oom killer. For
> some reason it refuses to drop pages before trying to kill. When it
> should drop cache, THEN kill if needed.

This isn't about OOM, but situation when you turn off overcommit. I was
jumping to conclusion here. You can drop caches manually with:
# echo 1 > /proc/sys/vm/drop_caches

but you still get: "malloc: Cannot allocate memory" even if almost
nothing is cached:

        total       used       free     shared    buffers     cached
Mem:    3458       2210       1248          0          3          90
-/+ buffers/cache: 2116       1342

As for not dropping pages by kernel before killing, I don't know nothing
about it. It happens so fast and I never tried to measure it.
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