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    SubjectRe: [PATCH] mm: check zone->all_unreclaimable in all_unreclaimable()
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    Hi Kame,

    Sorry for late response.
    I had a time to test this issue shortly because these day I am very busy.
    This issue was interesting to me.
    So I hope taking a time for enough testing when I have a time.
    I should find out root cause of livelock.

    I will answer your comment after it. :)
    Thanks!

    On Wed, Mar 9, 2011 at 2:37 PM, KAMEZAWA Hiroyuki
    <kamezawa.hiroyu@jp.fujitsu.com> wrote:
    > 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
    >
    >



    --
    Kind regards,
    Minchan Kim
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