linux-kernel - Re: [lkp] [mm, page_alloc] 43993977ba: +88% OOM possibility

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Date:	Mon, 2 Nov 2015 10:53:35 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	"Huang, Ying" <ying.huang@...ux.intel.com>
Cc:	Mel Gorman <mgorman@...hsingularity.net>, lkp@...org,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Vitaly Wool <vitalywool@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Christoph Lameter <cl@...ux.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [lkp] [mm, page_alloc] 43993977ba: +88% OOM possibility

On Mon 02-11-15 16:55:15, Huang, Ying wrote:
> Michal Hocko <mhocko@...nel.org> writes:
[...]
> > It would be interesting to see all the page allocation failure warnings
> > (if they are different). Maybe other callers have relied on GFP_ATOMIC
> > and access to memory reserves. The above path is not this case though.
> 
> I take a look at all dmesgs, and found the backtrace for page allocation
> failure is same for all.  Is it possible that this commit cause more
> memory were allocated or kept in memory so that more OOM were triggered?

I can imagine that some of the callers were not converted properly or
missed and a lack of __GFP_KSWAPD_RECLAIM could indeed cause a later
kswapd kick off. I am staring into the commit but nothing has jumped at
me yet. Could you collect /proc/vmstat (snapshot every 1s) on both good
and bad kernels. I expect the later would see a less scanning by kswapd.
-- 
Michal Hocko
SUSE Labs
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