linux-kernel - Re: tmpfs and the OOM killer

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Message-ID: <Pine.LNX.4.61.0704121011370.20436@yvahk01.tjqt.qr>
Date:	Thu, 12 Apr 2007 10:13:05 +0200 (MEST)
From:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
To:	Willy Tarreau <w@....eu>
cc:	Pedro <linux_user@...cksohn.com>, linux-kernel@...r.kernel.org
Subject: Re: tmpfs and the OOM killer


On Apr 11 2007 21:48, Willy Tarreau wrote:
>On Wed, Apr 11, 2007 at 02:23:31AM -0300, Pedro wrote:
>>   After suffering some days from a not|mis configured tmpfs,
>> 
>>   As the OOM killer is not Posix,
>> 
>>   Better than to kill processes would be to resize tmpfs, to use tmpfs empty 
>> space.
>
>Will not work, because tmpfs does not use any memory for unused space. If
>you don't believe me, simply create a large file on your tmpfs, then check
>free memory, then remove the file and check free memory again.
>
>So your problem is not caused by the empty space on tmpfs, but either by
>too much space used on tmpfs or by your application using too much memory.
>
>>   I'm using kernel 2.6.20.4. If someone ask I'll send a test application.
>
>Not needed, the one-liner "main(){while(malloc(4096));}" is enough to
>trigger an OOM.

No, that won't do anything, malloc happily returns NULL after a few seconds.

int main()
{
	while(1) {
		char *p = malloc(4096);
		*p = 1;
	}
}

This is more likely to trigger OOM, because it actually dirties the page.


Jan
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