linux-kernel - Re: [PATCH 1/9] HWPOISON, hugetlb: move PG

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Date:	Thu, 19 Aug 2010 17:28:28 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>,
	Jun'ichi Nomura <j-nomura@...jp.nec.com>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/9] HWPOISON, hugetlb: move PG_HWPoison bit check

On Thu, Aug 19, 2010 at 03:55:43PM +0800, Naoya Horiguchi wrote:
> On Wed, Aug 18, 2010 at 08:18:42AM +0800, Wu Fengguang wrote:
> > On Tue, Aug 10, 2010 at 05:27:36PM +0800, Naoya Horiguchi wrote:
> > > In order to handle metadatum correctly, we should check whether the hugepage
> > > we are going to access is HWPOISONed *before* incrementing mapcount,
> > > adding the hugepage into pagecache or constructing anon_vma.
> > > This patch also adds retry code when there is a race between
> > > alloc_huge_page() and memory failure.
> > 
> > This duplicates the PageHWPoison() test into 3 places without really
> > address any problem. For example, there are still _unavoidable_ races
> > between PageHWPoison() and add_to_page_cache().
> > 
> > What's the problem you are trying to resolve here? If there are
> > data structure corruption, we may need to do it in some other ways.
> 
> The problem I tried to resolve in this patch is the corruption of
> data structures when memory failure occurs between alloc_huge_page()
> and lock_page().
> The corruption occurs because page fault can fail with metadata changes
> remained (such as refcount, mapcount, etc.) 
> Since the PageHWPoison() check is for avoiding hwpoisoned page remained
> in pagecache mapping to the process, it should be done in
> "found in pagecache" branch, not in the common path.
> This patch moves the check to "found in pagecache" branch.

That's good stuff to put in the changelog.

> In addition to that, I added 2 PageHWPoison checks in "new allocation" branches
> to enhance the possiblity to recover from memory failures on pages under allocation.
> But it's a different point from the original one, so I drop these retry checks.

So you'll remove the first two chunks and retain the 3rd chunk?
That makes it a small bug-fix patch suitable for 2.6.36 and I'll
happily ACK it :)

Thanks,
Fengguang

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