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Date: Fri, 31 May 2013 12:30:03 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: linux-mm@kvack.org, Mel Gorman <mgorman@suse.de>,
        Andi Kleen <andi@firstfloor.org>, Michal Hocko <mhocko@suse.cz>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Rik van Riel <riel@redhat.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 2/2] migrate: add migrate_entry_wait_huge()
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On Tue, 28 May 2013 15:52:51 -0400 Naoya Horiguchi <n-horiguchi@ah.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@ah.jp.nec.com>
> Reviewed-by: Rik van Riel <riel@redhat.com>
> Cc: stable@vger.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).