linux-kernel - Re: [patch 08/11 -mmotm] oom: invoke oom killer for __GFP

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Date:	Mon, 11 May 2009 16:40:08 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Nick Piggin <npiggin@...e.de>, Mel Gorman <mel@....ul.ie>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	San Mehat <san@...roid.com>, Arve Hjonnevag <arve@...roid.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 08/11 -mmotm] oom: invoke oom killer for __GFP_NOFAIL

On Mon, 11 May 2009 10:45:05 +0900 (JST)
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:

> > On Mon, 11 May 2009, KOSAKI Motohiro wrote:
> > 
> > > > The oom killer must be invoked regardless of the order if the allocation
> > > > is __GFP_NOFAIL, otherwise it will loop forever when reclaim fails to
> > > > free some memory.
> > > 
> > > This is intensional behavior. plus you change very widely caller bahavior.
> > > if you don't have good test program, I nak this.
> > > 
> > 
> > What exactly are you objecting to?  You don't want the oom killer called 
> > for a __GFP_NOFAIL allocation above PAGE_ALLOC_COSTLY_ORDER that could not 
> > reclaim any memory and would prefer that it loop endlessly in the page 
> > allocator?  What's the purpose of that if the oom killer could free a very 
> > large memory hogging task?
> 
> My point is, if we change gfp-flags meaning, we should change
> unintentional affected caller.
> 
> Do you oppose this?
>

I agree KOSAKI's opinion. 
We already have a different flags. 

 * __GFP_REPEAT: Try hard to allocate the memory, but the allocation attempt
 * _might_ fail.  This depends upon the particular VM implementation.
 *
 * __GFP_NOFAIL: The VM implementation _must_ retry infinitely: the caller
 * cannot handle allocation failures.

When we use __GFP_NOFAIL, we always have to use it carefully.
If you change the meaning of __GFP_NOFAIL, the intension of them who have been used it carefully  may be lost. It's my concern.


-- 
Kinds Regards
Minchan Kim
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