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    SubjectRe: [PATCH 0/6] cpuset aware writeback
    Perform writeback and dirty throttling with awareness of cpuset mem_allowed.

    The theory of operation has two primary elements:

    1. Add a nodemask per mapping which indicates the nodes
    which have set PageDirty on any page of the mappings.

    2. Add a nodemask argument to wakeup_pdflush() which is
    propagated down to sync_sb_inodes.

    This leaves sync_sb_inodes() with two nodemasks. One is passed to it and
    specifies the nodes the caller is interested in syncing, and will either
    be null (i.e. all nodes) or will be cpuset_current_mems_allowed in the
    caller's context.

    The second nodemask is attached to the inode's mapping and shows who has
    modified data in the inode. sync_sb_inodes() will then skip syncing of
    inodes if the nodemask argument does not intersect with the mapping

    cpuset_current_mems_allowed will be passed in to pdflush
    background_writeout by try_to_free_pages and balance_dirty_pages.
    balance_dirty_pages also passes the nodemask in to writeback_inodes
    directly when doing active reclaim.

    Other callers do not limit inode writeback, passing in a NULL nodemask

    A final change is to get_dirty_limits. It takes a nodemask argument, and
    when it is null there is no change in behavior. If the nodemask is set,
    page statistics are accumulated only for specified nodes, and the
    background and throttle dirty ratios will be read from a new per-cpuset
    ratio feature.

    For testing I did a variety of basic tests, verifying individual
    features of the test. To verify that it fixes the core problem, I
    created a stress test which involved using cpusets and mems_allowed
    to split memory so that all daemons had memory set aside for them, and
    my memory stress test had a separate set of memory. The stress test was
    mmaping 7GB of a very large file on disk. It then scans the entire 7GB
    of memory reading and modifying each byte. 7GB is more than the amount
    of physical memory made available to the stress test.

    Using iostat I can see the initial period of reading from disk, followed
    by a period of simultaneous reads and writes as dirty bytes are pushed
    to make room for new reads.

    In a separate log-in, in the other cpuset, I am running:

    while `true`; do date | tee -a date.txt; sleep 5; done

    date.txt resides on the same disk as the large file mentioned above. The
    above while-loop serves the dual purpose of providing me visual clues of
    progress along with the opportunity for the "tee" command to become
    throttled writing to the disk.

    The effect of this patchset is straightforward. Without it there are
    long hangs between appearances of the date. With it the dates are all 5
    (or sometimes 6) seconds apart.

    I also added printks to the kernel to verify that, without these
    patches, the tee was being throttled (along with lots of other things),
    and with the patch only pdflush is being throttled.

    These patches are mostly unchanged from Chris Lameter's original
    changelist posted previously to linux-mm.

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      Last update: 2007-09-12 03:35    [W:0.023 / U:7.880 seconds]
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