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

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Date:	Mon, 11 May 2009 01:49:07 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Minchan Kim <minchan.kim@...il.com>
cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.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, Minchan Kim wrote:

> 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.
> 

You pointed out yourself that __GFP_NOFAIL allocations can fail by way of 
having alloc_pages() return NULL even without attempting to free memory by 
the oom killer for order > PAGE_ALLOC_COSTLY_ORDER.  The definition you 
posted above is unambiguous to me, it means we must retry infinitely.  And 
that's very stupid if we are going to neglect to free memory by killing a 
task and relying solely on reclaim which may not make any progress.
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