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

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Date:	Fri, 31 May 2013 12:30:03 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	linux-mm@...ck.org, Mel Gorman <mgorman@...e.de>,
	Andi Kleen <andi@...stfloor.org>,
	Michal Hocko <mhocko@...e.cz>,
	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 Tue, 28 May 2013 15:52:51 -0400 Naoya Horiguchi <n-horiguchi@...jp.nec.com> 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

That changelog is not suitable for a -stable patch.  People who
maintain and utilize the stable trees need to know in some detail what
is the end-user impact of the patch (or, equivalently, of the bug
which the patch fixes).

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