linux-kernel - Re: [PATCH 1/9] migrate: add migrate_entry_wait

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Message-ID: <1363816399-c6e7mofc-mutt-n-horiguchi@ah.jp.nec.com>
Date:	Wed, 20 Mar 2013 17:53:19 -0400
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Simon Jeons <simon.jeons@...il.com>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, Hugh Dickins <hughd@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/9] migrate: add migrate_entry_wait_huge()

On Wed, Mar 20, 2013 at 07:57:32AM +0800, Simon Jeons wrote:
> Hi Naoya,
> On 02/22/2013 03:41 AM, Naoya Horiguchi wrote:
> >When we have a page fault for the address which is backed by a hugepage
> >under migration, the kernel can't wait correctly until the migration
> >finishes. This is because pte_offset_map_lock() can't get a correct
> 
> It seems that current hugetlb_fault still wait hugetlb page under
> migration, how can it work without lock 2MB memory?

Hugetlb_fault() does call migration_entry_wait(), but returns immediately.
So page fault happens over and over again until the migration completes.
IOW, migration_entry_wait() is now broken for hugepage and doesn't work
as expected.

Thanks,
Naoya
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