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    SubjectRE: [PATCH -v2 -mm] add extra free kbytes tunable
    On 10/11/2011 03:55 PM, Andrew Morton wrote:
    > On Tue, 11 Oct 2011 15:32:11 -0400
    > Satoru Moriya <satoru.moriya@hds.com> wrote:
    >
    >> On 10/10/2011 06:37 PM, Andrew Morton wrote:
    >>> On Fri, 7 Oct 2011 20:08:19 -0700 (PDT) David Rientjes
    >>> <rientjes@google.com> wrote:
    >>>
    >>>> On Thu, 1 Sep 2011, Rik van Riel wrote:
    >>
    >> Actually page allocator decreases min watermark to 3/4 * min
    >> watermark for rt-task. But in our case some applications create a lot
    >> of processes and if all of them are rt-task, the amount of watermark
    >> bonus(1/4 * min watermark) is not enough.
    >>
    >> If we can tune the amount of bonus, it may be fine. But that is
    >> almost all same as extra free kbytes.
    >
    > This situation is detectable at runtime. If realtime tasks are being
    > stalled in the page allocator then start to increase the free-page
    > reserves. A little control system.

    Detecting at runtime is too late for some latency critical systems.
    At that system, we must avoid a stall before it happens.

    Also, if we increase the free-page reserves a.k.a min_free_kbytes,
    the possibility of direct reclaim on other workloads increases.
    I think it's a bad side effect.

    Thanks,
    Satoru


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