linux-kernel - Re: [patch] mm, thp: abort compaction if migration page cannot be charged to memcg

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Date:	Thu, 21 Jun 2012 02:01:44 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Minchan Kim <minchan@...nel.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch] mm, thp: abort compaction if migration page cannot be
 charged to memcg

On Thu, 21 Jun 2012, David Rientjes wrote:

> It's possible that subsequent pageblocks would contain memory allocated 
> from solely non-oom memcgs, but it's certainly not a guarantee and results 
> in terrible performance as exhibited above.  Is there another good 
> criteria to use when deciding when to stop isolating and attempting to 
> migrate all of these pageblocks?
> 
> Other ideas?
> 

The only other alternative that I can think of is to check 
mem_cgroup_margin() in isolate_migratepages_range() and return a NULL 
lruvec that would break that pageblock and return, and then set a bit in 
struct mem_cgroup that labels it as oom so we can check for it on 
subsequent pageblocks without incurring the locking to do 
mem_cgroup_margin() in res_counter, and then clear that bit on every 
uncharge to a memcg, but this still seems like a tremendous waste of cpu 
(especially if /sys/kernel/mm/transparent_hugepage/defrag == always) if 
most pageblocks contain pages from an oom memcg.
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