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

Zi Yan [off-list ref] writes:

Huang, Ying wrote:

quoted

"Kirill A. Shutemov" [off-list ref] writes:

quoted

On Tue, Oct 17, 2017 at 04:18:18PM +0800, Huang, Ying wrote:

quoted

From: Huang Ying <redacted>

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@suse.com>
Cc: "Kirill A. Shutemov" <redacted>
Cc: David Rientjes <rientjes@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: "J.r.me Glisse" <redacted>
Cc: Daniel Colascione <redacted>
Cc: Zi Yan <redacted>
Cc: Naoya Horiguchi <redacted>
Signed-off-by: "Huang, Ying" <redacted>

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.

quoted

quoted

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

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