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    SubjectRe: [PATCH -mm] vmscan: bail out of page reclaim after swap_cluster_max pages
    KAMEZAWA Hiroyuki wrote:
    > On Sun, 16 Nov 2008 16:38:56 +0900 (JST)
    > KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
    >
    >> One more point.
    >>
    >>> Sometimes the VM spends the first few priority rounds rotating back
    >>> referenced pages and submitting IO. Once we get to a lower priority,
    >>> sometimes the VM ends up freeing way too many pages.
    >>>
    >>> The fix is relatively simple: in shrink_zone() we can check how many
    >>> pages we have already freed and break out of the loop.
    >>>
    >>> However, in order to do this we do need to know how many pages we already
    >>> freed, so move nr_reclaimed into scan_control.
    >> IIRC, Balbir-san explained the implemetation of the memcgroup
    >> force cache dropping feature need non bail out at the past reclaim
    >> throttring discussion.
    >>

    Yes, for we used that for force_empty() in the past, but see below

    >> I am not sure about this still right or not (iirc, memcgroup implemetation
    >> was largely changed).
    >>
    >> Balbir-san, Could you comment to this patch?
    >>
    >>
    > I'm not Balbir-san but there is no "force-cache-dropping" feature now.
    > (I have no plan to do that.)
    >
    > But, mem+swap controller will need to modify reclaim path to do "cache drop
    > first" becasue the amount of "mem+swap" will not change when "mem+swap" hit
    > limit. It's now set "sc.may_swap" to 0.
    >

    Yes, there have been several changes to force_empty() and its meaning, including
    movement of accounts. Since you've made most of the recent changes, your
    comments are very relevant.

    > Hmm, I hope memcg is a silver bullet to this kind of special? workload in
    > long term.

    :-) From my perspective, hierarchy, soft limits (sharing memory when there is no
    contention), some form of over commit support and getting swappiness to work
    correctly are very important for memcg.

    --
    Balbir


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