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Date: Fri, 9 Apr 2010 01:17:05 +0200
From: Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH 00 of 67] Transparent Hugepage Support #18
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Cc: Avi Kivity <avi@redhat.com>, linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>, Marcelo Tosatti <mtosatti@redhat.com>, Adam Litke <agl@us.ibm.com>, Izik Eidus <ieidus@redhat.com>, Hugh Dickins <hugh.dickins@tiscali.co.uk>, Nick Piggin <npiggin@suse.de>, Rik van Riel <riel@redhat.com>, Mel Gorman <mel@csn.ul.ie>, Dave Hansen <dave@linux.vnet.ibm.com>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Ingo Molnar <mingo@elte.hu>, Mike Travis <travis@sgi.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Chris Wright <chrisw@sous-sol.org>, bpicco@redhat.com, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Balbir Singh <balbir@linux.vnet.ibm.com>, "Michael S. Tsirkin" <mst@redhat.com>, Peter Zijlstra <peterz@infradead.org>, Johannes Weiner <hannes@cmpxchg.org>, Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>, Chris Mason <chris.mason@oracle.com>, Linus Torvalds <torvalds@linux-foundation.org>
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This may have been caused by the same anon-vma bug that is being
debugged for mainline as it'd free anon-vma too early leading to
memory corruption. split_huge_page is a super heavy user of anon-vmas,
so that would explain all the issues, and also another crash I had in
split_huge_page where the rmap chain found a number of pmd mapping the
hugepage different than page_mapcount. For swap that means mlock, for
split_huge_page not being able to update some huge pmd is fatal so
there's plenty of BUG_ON to check all goes well and there's no risk of
corruption later on.

We need to test with Linus's fix for anon-vma bug, and I guess
everything will go fine when that bug is solved.

I added more commentary as well to cover an ordering issue in the
anon_vma_prepare.

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