linux-kernel - Re: [patch -mm 8/9 v2] oom: avoid oom killer for lowmem allocations

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Date:	Mon, 15 Feb 2010 23:29:17 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.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 -mm 8/9 v2] oom: avoid oom killer for lowmem
 allocations

On Tue, 16 Feb 2010, KOSAKI Motohiro wrote:

> No current user? I don't think so.
> 
> 	int bio_integrity_prep(struct bio *bio)
> 	{
> 	(snip)
> 	        buf = kmalloc(len, GFP_NOIO | __GFP_NOFAIL | q->bounce_gfp);
> 
> and 
> 
> 	void blk_queue_bounce_limit(struct request_queue *q, u64 dma_mask)
> 	{
> 	(snip)
> 	        if (dma) {
> 	                init_emergency_isa_pool();
> 	                q->bounce_gfp = GFP_NOIO | GFP_DMA;
> 	                q->limits.bounce_pfn = b_pfn;
> 	        }
> 
> 
> 
> I don't like rumor based discussion, I like fact based one.
> 

The GFP_NOIO will prevent the oom killer from being called, it requires 
__GFP_FS.

I can change this to invoke the should_alloc_retry() logic by testing for 
!(gfp_mask & __GFP_NOFAIL), but there's nothing else the page allocator 
can currently do to increase its probability of allocating pages; the 
memory compaction patchset might be particularly helpful for these types 
of scenarios.
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