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    Subject[PATCH v2 0/4] enhance shmem process and swap accounting
    Date
    Changes since v1:
    o In Patch 2, rely on SHMEM_I(inode)->swapped if possible, and fallback to
    radix tree iterator on partially mapped shmem objects, i.e. decouple shmem
    swap usage determination from the page walk, for performance reasons.
    Thanks to Jerome and Konstantin for the tips.
    The downside is that mm/shmem.c had to be touched.

    This series is based on Jerome Marchand's [1] so let me quote the first
    paragraph from there:

    There are several shortcomings with the accounting of shared memory
    (sysV shm, shared anonymous mapping, mapping to a tmpfs file). The
    values in /proc/<pid>/status and statm don't allow to distinguish
    between shmem memory and a shared mapping to a regular file, even
    though theirs implication on memory usage are quite different: at
    reclaim, file mapping can be dropped or write back on disk while shmem
    needs a place in swap. As for shmem pages that are swapped-out or in
    swap cache, they aren't accounted at all.

    The original motivation for myself is that a customer found (IMHO rightfully)
    confusing that e.g. top output for process swap usage is unreliable with
    respect to swapped out shmem pages, which are not accounted for.

    The fundamental difference between private anonymous and shmem pages is that
    the latter has PTE's converted to pte_none, and not swapents. As such, they are
    not accounted to the number of swapents visible e.g. in /proc/pid/status VmSwap
    row. It might be theoretically possible to use swapents when swapping out shmem
    (without extra cost, as one has to change all mappers anyway), and on swap in
    only convert the swapent for the faulting process, leaving swapents in other
    processes until they also fault (so again no extra cost). But I don't know how
    many assumptions this would break, and it would be too disruptive change for a
    relatively small benefit.

    Instead, my approach is to document the limitation of VmSwap, and provide means
    to determine the swap usage for shmem areas for those who are interested and
    willing to pay the price, using /proc/pid/smaps. Because outside of ipcs, I
    don't think it's possible to currently to determine the usage at all. The
    previous patchset [1] did introduce new shmem-specific fields into smaps
    output, and functions to determine the values. I take a simpler approach,
    noting that smaps output already has a "Swap: X kB" line, where currently X ==
    0 always for shmem areas. I think we can just consider this a bug and provide
    the proper value by consulting the radix tree, as e.g. mincore_page() does. In the
    patch changelog I explain why this is also not perfect (and cannot be without
    swapents), but still arguably much better than showing a 0.

    The last two patches are adapted from Jerome's patchset and provide a VmRSS
    breakdown to VmAnon, VmFile and VmShm in /proc/pid/status. Hugh noted that
    this is a welcome addition, and I agree that it might help e.g. debugging
    process memory usage at albeit non-zero, but still rather low cost of extra
    per-mm counter and some page flag checks. I updated these patches to 4.0-rc1,
    made them respect !CONFIG_SHMEM so that tiny systems don't pay the cost, and
    optimized the page flag checking somewhat.

    [1] http://lwn.net/Articles/611966/

    Jerome Marchand (2):
    mm, shmem: Add shmem resident memory accounting
    mm, procfs: Display VmAnon, VmFile and VmShm in /proc/pid/status

    Vlastimil Babka (2):
    mm, documentation: clarify /proc/pid/status VmSwap limitations
    mm, proc: account for shmem swap in /proc/pid/smaps

    Documentation/filesystems/proc.txt | 15 +++++++++--
    arch/s390/mm/pgtable.c | 5 +---
    fs/proc/task_mmu.c | 52 ++++++++++++++++++++++++++++++++++--
    include/linux/mm.h | 28 ++++++++++++++++++++
    include/linux/mm_types.h | 9 ++++---
    include/linux/shmem_fs.h | 6 +++++
    kernel/events/uprobes.c | 2 +-
    mm/memory.c | 30 +++++++--------------
    mm/oom_kill.c | 5 ++--
    mm/rmap.c | 15 +++--------
    mm/shmem.c | 54 ++++++++++++++++++++++++++++++++++++++
    11 files changed, 176 insertions(+), 45 deletions(-)

    --
    2.1.4



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