linux-kernel - Re: [PATCH 1/7] hugetlb, rmap: add reverse mapping for hugepage

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Message-ID: <87zl04tb1v.fsf@basil.nowhere.org>
Date:	Thu, 13 May 2010 11:18:04 +0200
From:	Andi Kleen <andi@...obates.de>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Mel Gorman <mel@....ul.ie>, aarcange@...hat.com,
	lwoodman@...hat.com, Lee.Schermerhorn@...com
Subject: Re: [PATCH 1/7] hugetlb, rmap: add reverse mapping for hugepage

Naoya Horiguchi <n-horiguchi@...jp.nec.com> writes:

Adding a few more recent hugetlb hackers in cc. Folks, please consider
reviewing the hugetlb.c parts of the original patch kit in linux-mm.

> While hugepage is not currently swappable, rmapping can be useful
> for memory error handler.
> Using rmap, memory error handler can collect processes affected
> by hugepage errors and unmap them to contain error's effect.

Thanks.

I reviewed all the patches and they look good to me. I can merge
them through the hwpoison git tree.

But before merging it there I would like to have some review
and acks from mm hackers on the mm/hugetlb.c parts, which
do (relatively minor) changes outside memory-failure.c

I think you also had a patch for mce-test, can you send me that
one too?

BTW I wonder: did you verify that the 1GB page support works?
I would expect it does, but it would be good to double check.
One would need a Westmere server or AMD Family10h+ system to test that.

> Current status of hugepage rmap differs depending on mapping mode:
> - for shared hugepage:
>   we can collect processes using a hugepage through pagecache,
>   but can not unmap the hugepage because of the lack of mapcount.
> - for privately mapped hugepage:
>   we can neither collect processes nor unmap the hugepage.

I hope these points can be eventually addressed too, but this
is a good first step and closes an important hole in hwpoison
coverage.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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