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    Subject[PATCH 0/3] Avoid dirtying pages during mlock
    As discussed in linux-mm, mlocking a shared, writable vma currently causes
    the corresponding pages to be marked as dirty and queued for writeback.
    This seems rather unnecessary given that the pages are not being actually
    modified during mlock. It is understood that for non-shared mappings
    (file or anon) we want to use a write fault in order to break COW, but
    there is just no such need for shared mappings.

    The first two patches in this series do not introduce any behavior change.
    The intent there is to make it obvious that dirtying file pages is
    only done in the (writable, shared) case. I think this clarifies the
    code, but I wouldn't mind dropping these two patches if there is no
    consensus about them.

    The last patch is where we actually avoid dirtying shared mappings
    during mlock. Note that as a side effect of this, we won't call
    page_mkwrite() for the mappings that define it, and won't be
    pre-allocating data blocks at the FS level if the mapped file was
    sparsely allocated. My understanding is that mlock does not need to
    provide such guarantee, as evidenced by the fact that it never did for
    the filesystems that don't define page_mkwrite() - including some
    common ones like ext3. However, I would like to gather feedback on this
    from filesystem people as a precaution. If this turns out to be a
    showstopper, maybe block preallocation can be added back on using a
    different interface.

    Large shared mlocks are getting significantly (>2x) faster in my tests,
    as the disk can be fully used for reading the file instead of having to
    share between this and writeback.

    Michel Lespinasse (3):
    do_wp_page: remove the 'reuse' flag
    do_wp_page: clarify dirty_page handling
    mlock: avoid dirtying pages and triggering writeback

    mm/memory.c | 90 ++++++++++++++++++++++++++++++++---------------------------
    mm/mlock.c | 7 ++++-
    2 files changed, 55 insertions(+), 42 deletions(-)


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