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

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Date:   Tue, 17 Oct 2017 21:55:12 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Zi Yan <zi.yan@...rutgers.edu>
Cc:     "Huang\, Ying" <ying.huang@...el.com>,
        "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

Zi Yan <zi.yan@...rutgers.edu> writes:

> 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?

Oh, if so, I think we don't need to back port it to stable kernel.  But
we still need Fixes: tag.

Best Regards,
Huang, Ying