linux-kernel - Re: [PATCH v3 2/2] migrate: add migrate_entry_wait

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Message-ID: <1370270081-pv4wkd99-mutt-n-horiguchi@ah.jp.nec.com>
Date:	Mon, 03 Jun 2013 10:34:41 -0400
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Andi Kleen <andi@...stfloor.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] migrate: add migrate_entry_wait_huge()

On Mon, Jun 03, 2013 at 03:26:41PM +0200, Michal Hocko wrote:
> On Tue 28-05-13 15:52:51, 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 and do busy looping on
> > hugepage fault until the migration finishes.
> > This is because pte_offset_map_lock() can't get a correct migration entry
> > or a correct page table lock for hugepage.
> > This patch introduces migration_entry_wait_huge() to solve this.
> > 
> > Note that the caller, hugetlb_fault(), gets the pointer to the "leaf"
> > entry with huge_pte_offset() inside which all the arch-dependency of
> > the page table structure are. So migration_entry_wait_huge() and
> > __migration_entry_wait() are free from arch-dependency.
> > 
> > ChangeLog v3:
> >  - use huge_pte_lockptr
> > 
> > ChangeLog v2:
> >  - remove dup in migrate_entry_wait_huge()
> > 
> > Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> > Reviewed-by: Rik van Riel <riel@...hat.com>
> > Cc: stable@...r.kernel.org # 2.6.35
> 
> OK, this looks good to me and I guess you can safely replace
> huge_pte_lockptr by &(mm)->page_table_lock so you can implement this
> even without risky 1/2 of this series. The patch should be as simple as
> possible especially when it goes to the stable.

Yes, I agree.

> > Without 1/2 dependency
> Reviewed-by: Michal Hocko <mhocko@...e.cz>

Thanks,
Naoya
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