linux-kernel - Re: [PATCH -mm] mm, pagemap: Fix soft dirty marking for PMD migration entry

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Date:   Tue, 17 Oct 2017 08:33:05 -0400
From:   Zi Yan <zi.yan@...rutgers.edu>
To:     "Huang, Ying" <ying.huang@...el.com>
CC:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Arnd Bergmann <arnd@...db.de>, Hugh Dickins <hughd@...gle.com>,
        J�r�me Glisse <jglisse@...hat.com>,
        Daniel Colascione <dancol@...gle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Subject: Re: [PATCH -mm] mm, pagemap: Fix soft dirty marking for PMD migration
 entry



Huang, Ying wrote:
> "Kirill A. Shutemov" <kirill@...temov.name> writes:
> 
>> On Tue, Oct 17, 2017 at 04:18:18PM +0800, Huang, Ying wrote:
>>> From: Huang Ying <ying.huang@...el.com>
>>>
>>> Now, when the page table is walked in the implementation of
>>> /proc/<pid>/pagemap, pmd_soft_dirty() is used for both the PMD huge
>>> page map and the PMD migration entries.  That is wrong,
>>> pmd_swp_soft_dirty() should be used for the PMD migration entries
>>> instead because the different page table entry flag is used.
>>>
>>> Cc: Michal Hocko <mhocko@...e.com>
>>> Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
>>> Cc: David Rientjes <rientjes@...gle.com>
>>> Cc: Arnd Bergmann <arnd@...db.de>
>>> Cc: Hugh Dickins <hughd@...gle.com>
>>> Cc: "J.r.me Glisse" <jglisse@...hat.com>
>>> Cc: Daniel Colascione <dancol@...gle.com>
>>> Cc: Zi Yan <zi.yan@...rutgers.edu>
>>> Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
>>> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
>> What is effect of the misbehaviour? pagemap reports garbage?
> 
> Yes.  pagemap may report incorrect soft dirty information for PMD
> migration entries.

Thanks for fixing it.

> 
>> Shoudn't it be in stable@? And maybe add Fixes: <sha1>.
> 
> Yes.  Will do that in the next version.

PMD migration is merged in 4.14, which is not final yet. Do we need to
split the patch, so that first hunk(for present PMD entries) goes into
stable and second hunk(for PMD migration entries) goes into 4.14?

-- 
Best Regards,
Yan Zi


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