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    SubjectRe: [patch] memcg: skip scanning active lists based on individual size
    On Wed, 31 Aug 2011 19:13:34 +0900
    Minchan Kim <minchan.kim@gmail.com> wrote:

    > On Wed, Aug 31, 2011 at 6:08 PM, Johannes Weiner <jweiner@redhat.com> wrote:
    > > Reclaim decides to skip scanning an active list when the corresponding
    > > inactive list is above a certain size in comparison to leave the
    > > assumed working set alone while there are still enough reclaim
    > > candidates around.
    > >
    > > The memcg implementation of comparing those lists instead reports
    > > whether the whole memcg is low on the requested type of inactive
    > > pages, considering all nodes and zones.
    > >
    > > This can lead to an oversized active list not being scanned because of
    > > the state of the other lists in the memcg, as well as an active list
    > > being scanned while its corresponding inactive list has enough pages.
    > >
    > > Not only is this wrong, it's also a scalability hazard, because the
    > > global memory state over all nodes and zones has to be gathered for
    > > each memcg and zone scanned.
    > >
    > > Make these calculations purely based on the size of the two LRU lists
    > > that are actually affected by the outcome of the decision.
    > >
    > > Signed-off-by: Johannes Weiner <jweiner@redhat.com>
    > > Cc: Rik van Riel <riel@redhat.com>
    > > Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    > > Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > > Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
    > > Cc: Balbir Singh <bsingharora@gmail.com>
    >
    > Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
    >
    > I can't understand why memcg is designed for considering all nodes and zones.
    > Is it a mistake or on purpose?

    It's purpose. memcg just takes care of the amount of pages.
    Them, any performance numbers ?


    But, hmm, this change may be good for softlimit and your work.

    I'll ack when you add performance numbers in changelog.

    Thanks,
    -Kame



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