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    SubjectRe: [RFC][PATCH] page reclaim throttle take2
    On Tue, 26 Feb 2008 23:19:08 -0800 (PST)
    David Rientjes <> wrote:
    > My suggestion is merely to make the number of concurrent page reclaim
    > threads be a function of how many online cpus there are. Threads can
    > easily be added or removed for cpu hotplug events by callback functions.
    > That's different than allowing users to change the number of threads with
    > yet another sysctl. Unless there are situations that can be presented
    > where tuning the number of threads is advantageous to reduce lock
    > contention, for example, and not simply working around other VM problems,
    > then I see no point for an additional sysctl.
    > So my suggestion is to implement this in terms of
    > CONFIG_NUM_RECLAIM_THREADS_PER_CPU and add callback functions for cpu
    > hotplug events that add or remove this number of threads.

    Hmm, but kswapd, which is main worker of page reclaiming, is per-node.
    And reclaim is done based on zone.
    per-zone/per-node throttling seems to make sense.

    I know his environment has 4cpus per node but throttle to 3 was the best
    number in his measurement. Then it seems num-per-cpu is excessive.
    (At least, ratio(%) is better.)
    When zone-reclaiming is improved to be scale well, we'll have to change
    this throttle.

    BTW, could someone try his patch on x86_64/ppc ?
    I'd like to see how contention is heavy on other machines.


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