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    SubjectRe: [PATCH] mm: check zone->all_unreclaimable in all_unreclaimable()
    On Tue, 8 Mar 2011 08:45:51 +0900
    Minchan Kim <minchan.kim@gmail.com> wrote:

    > On Tue, Mar 8, 2011 at 6:58 AM, Andrew Morton <akpm@linux-foundation.org> wrote:
    > > On Sun, 6 Mar 2011 02:07:59 +0900
    > > Minchan Kim <minchan.kim@gmail.com> wrote:
    > > Any alternative proposals?  We should get the livelock fixed if possible..
    > >
    >
    > And we should avoid unnecessary OOM kill if possible.
    >
    > I think the problem is caused by (zone->pages_scanned <
    > zone_reclaimable_pages(zone) * 6). I am not sure (* 6) is a best. It
    > would be rather big on recent big DRAM machines.
    >

    It means 3 times full-scan from the highest priority to the lowest
    and cannot freed any pages. I think big memory machine tend to have
    more cpus, so don't think it's big.

    > I think it is a trade-off between latency and OOM kill.
    > If we decrease the magic value, maybe we should prevent the almost
    > livelock but happens unnecessary OOM kill.
    >

    Hmm, should I support a sacrifice feature 'some signal(SIGINT?) will be sent by
    the kernel when it detects system memory is in short' in cgroup ?
    (For example, if full LRU scan is done in a zone, notifier
    works and SIGINT will be sent.)

    > And I think zone_reclaimable not fair.
    > For example, too many scanning makes reclaimable state to
    > unreclaimable state. Maybe it takes a very long time. But just some
    > page free makes unreclaimable state to reclaimabe with very easy. So
    > we need much painful reclaiming for changing reclaimable state with
    > unreclaimabe state. it would affect latency very much.
    >
    > Maybe we need more smart zone_reclaimabe which is adaptive with memory pressure.
    >
    I agree.

    Thanks,
    -Kame

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