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Re: [1/1] mm: thp: calculate the mapcount correctly for THP pages during WP faults

From Mike Marciniszyn <mike.marciniszyn@intel.com>
Newsgroups linux.kernel
Subject Re: [1/1] mm: thp: calculate the mapcount correctly for THP pages during WP faults
Date 2016-05-11 23:30 +0200
Message-ID <rxJRE-8eX-19@gated-at.bofh.it> (permalink)
References <rxlvZ-Gw-41@gated-at.bofh.it>
Organization linux.* mail to news gateway

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>
>Reviewed-by: "Kirill A. Shutemov" <kirill@shutemov.name>
>Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
>

Our RDMA tests are seeing an issue with memory locking that bisects to
commit 61f5d698cc97 ("mm: re-enable THP").

The test program registers two rather large MRs (512M) and RDMA writes
data to a passive peer using the first and RDMA reads it back into the
second MR and compares that data.  The sizes are chosen randomly between
0 and 1024 bytes.

The test will get through a few (<= 4 iterations) and then gets a compare error.

Tracing indicates the kernel logical addresses associated with the individual
pages at registration ARE correct , the data in the "RDMA read response only"
packets ARE correct.

The “corruption” occurs when the packet crosse two pages that are not
physically contiguous.   The second page reads back as zero in the program.

It looks like the user VA at the point of the compare error no longer points
to the same physical address as was registered.  

This patch totally resolves the issue!

Tested-by: Mike Marciniszyn <mike.marciniszy@intel.com>
Tested-by: Josh Collier <josh.d.collier@intel.com>

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Thread

[PATCH 0/3] mm: thp: mapcount updates Andrea Arcangeli <aarcange@redhat.com> - 2016-05-06 17:10 +0200
  [PATCH 2/3] mm: thp: microoptimize compound_mapcount() Andrea Arcangeli <aarcange@redhat.com> - 2016-05-06 17:10 +0200
    Re: [PATCH 2/3] mm: thp: microoptimize compound_mapcount() "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-05-06 19:40 +0200
  [PATCH 1/3] mm: thp: calculate the mapcount correctly for THP pages during WP faults Andrea Arcangeli <aarcange@redhat.com> - 2016-05-06 17:10 +0200
    Re: [PATCH 1/3] mm: thp: calculate the mapcount correctly for THP  pages during WP faults Alex Williamson <alex.williamson@redhat.com> - 2016-05-07 00:20 +0200
    Re: [PATCH 1/3] mm: thp: calculate the mapcount correctly for THP  pages during WP faults Andrew Morton <akpm@linux-foundation.org> - 2016-05-10 00:30 +0200
    [PATCH 1/1] mm: thp: calculate the mapcount correctly for THP pages during WP faults Andrea Arcangeli <aarcange@redhat.com> - 2016-05-10 21:30 +0200
      Re: [1/1] mm: thp: calculate the mapcount correctly for THP pages during WP faults Mike Marciniszyn <mike.marciniszyn@intel.com> - 2016-05-11 23:30 +0200
      [PATCH 1/1] mm: thp: calculate the mapcount correctly for THP pages during WP faults Andrea Arcangeli <aarcange@redhat.com> - 2016-05-12 18:40 +0200
        Re: [1/1] mm: thp: calculate the mapcount correctly for THP pages during WP faults Mike Marciniszyn <mike.marciniszyn@intel.com> - 2016-05-12 20:50 +0200
  [PATCH 3/3] mm: thp: split_huge_pmd_address() comment improvement Andrea Arcangeli <aarcange@redhat.com> - 2016-05-06 17:10 +0200
    Re: [PATCH 3/3] mm: thp: split_huge_pmd_address() comment improvement "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-05-06 19:40 +0200

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