linux-kernel - Re: [patch 6/7 -mm] oom: avoid oom killer for lowmem allocations

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Date:	Thu, 11 Feb 2010 09:08:58 -0500
From:	Rik van Riel <riel@...hat.com>
To:	David Rientjes <rientjes@...gle.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Lubos Lunak <l.lunak@...e.cz>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch 6/7 -mm] oom: avoid oom killer for lowmem allocations

On 02/11/2010 04:19 AM, David Rientjes wrote:
> On Wed, 10 Feb 2010, Rik van Riel wrote:
>
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -1914,6 +1914,9 @@ rebalance:
>>>    	 * running out of options and have to consider going OOM
>>>    	 */
>>>    	if (!did_some_progress) {
>>> +		/* The oom killer won't necessarily free lowmem */
>>> +		if (high_zoneidx<   ZONE_NORMAL)
>>> +			goto nopage;
>>>    		if ((gfp_mask&   __GFP_FS)&&   !(gfp_mask&   __GFP_NORETRY)) {
>>>    			if (oom_killer_disabled)
>>>    				goto nopage;
>>
>> Are there architectures that only have one memory zone?
>>
>
> It actually ends up not to matter because of how gfp_zone() is implemented
> (and you can do it with mem= on architectures with larger ZONE_DMA zones
> such as ia64).  ZONE_NORMAL is always guaranteed to be defined regardless
> of architecture or configuration because it's the default zone for memory
> allocation unless specified by a bit in GFP_ZONEMASK, it doesn't matter
> whether it actually has memory or not.  high_zoneidx in this case is just
> gfp_zone(gfp_flags) which always defaults to ZONE_NORMAL when one of the
> GFP_ZONEMASK bits is not set.  Thus, the only way to for the conditional
> in this patch to be true is when __GFP_DMA, or __GFP_DMA32 for x86_64, is
> passed to the page allocator and CONFIG_ZONE_DMA or CONFIG_ZONE_DMA32 is
> enabled, respectively.

Fair enough.

Acked-by: Rik van Riel <riel@...hat.com>

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