linux-kernel - Re: [PATCH] mm: compaction: Abort compaction if too many pages are isolated and caller is asynchronous

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Date:	Wed, 1 Jun 2011 18:58:09 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Minchan Kim <minchan.kim@...il.com>, akpm@...ux-foundation.org,
	Ury Stankevich <urykhy@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, stable@...nel.org
Subject: Re: [PATCH] mm: compaction: Abort compaction if too many pages are
 isolated and caller is asynchronous

On Wed, Jun 01, 2011 at 01:57:47AM +0100, Mel Gorman wrote:
> On Tue, May 31, 2011 at 04:14:02PM +0200, Andrea Arcangeli wrote:
> > On Tue, May 31, 2011 at 10:33:40PM +0900, Minchan Kim wrote:
> > > I checked them before sending patch but I got failed to find strange things. :(
> > 
> > My review also doesn't show other bugs in migrate_pages callers like
> > that one.
> > 
> > > Now I am checking the page's SwapBacked flag can be changed
> > > between before and after of migrate_pages so accounting of NR_ISOLATED_XX can
> > > make mistake. I am approaching the failure, too. Hmm.
> > 
> > When I checked that, I noticed the ClearPageSwapBacked in swapcache if
> > radix insertion fails, but that happens before adding the page in the
> > LRU so it shouldn't have a chance to be isolated.
> > 
> 
> After hammering three machines for several hours, I managed to trigger
> this once on x86 !CONFIG_SMP CONFIG_PREEMPT HIGHMEM4G (so no PAE)
> and caught the following trace.
> 

Umm, HIGHMEM4G implies a two-level pagetable layout so where are
things like _PAGE_BIT_SPLITTING being set when THP is enabled?

-- 
Mel Gorman
SUSE Labs
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