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Re: [PATCH 09/14] mm: use compaction feedback for thp backoff conditions

From Michal Hocko <mhocko@kernel.org>
Newsgroups linux.kernel
Subject Re: [PATCH 09/14] mm: use compaction feedback for thp backoff conditions
Date 2016-04-28 14:40 +0200
Message-ID <rsToB-36j-13@gated-at.bofh.it> (permalink)
References <rq6im-4F2-9@gated-at.bofh.it> <rq6io-4F2-55@gated-at.bofh.it> <rsPXI-hT-19@gated-at.bofh.it>
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On Thu 28-04-16 10:53:18, Vlastimil Babka wrote:
> On 04/20/2016 09:47 PM, Michal Hocko wrote:
> >From: Michal Hocko <mhocko@suse.com>
> >
> >THP requests skip the direct reclaim if the compaction is either
> >deferred or contended to reduce stalls which wouldn't help the
> >allocation success anyway. These checks are ignoring other potential
> >feedback modes which we have available now.
> >
> >It clearly doesn't make much sense to go and reclaim few pages if the
> >previous compaction has failed.
> >
> >We can also simplify the check by using compaction_withdrawn which
> >checks for both COMPACT_CONTENDED and COMPACT_DEFERRED. This check
> >is however covering more reasons why the compaction was withdrawn.
> >None of them should be a problem for the THP case though.
> >
> >It is safe to back of if we see COMPACT_SKIPPED because that means
> >that compaction_suitable failed and a single round of the reclaim is
> >unlikely to make any difference here. We would have to be close to
> >the low watermark to reclaim enough and even then there is no guarantee
> >that the compaction would make any progress while the direct reclaim
> >would have caused the stall.
> >
> >COMPACT_PARTIAL_SKIPPED is slightly different because that means that we
> >have only seen a part of the zone so a retry would make some sense. But
> >it would be a compaction retry not a reclaim retry to perform. We are
> >not doing that and that might indeed lead to situations where THP fails
> >but this should happen only rarely and it would be really hard to
> >measure.
> >
> >Signed-off-by: Michal Hocko <mhocko@suse.com>
> 
> THP's don't compact by default in page fault path anymore, so we don't need
> to restrict them even more. And hopefully we'll replace the
> is_thp_gfp_mask() hack with something better soon, so this might be just
> extra code churn. But I don't feel strongly enough to nack it.

My main point was to simplify the code and get rid of as much compaction
specific hacks as possible. We might very well drop this later on but it
would be at least less code to grasp through. I do not have any problem
with dropping this but I think this shouldn't collide with other patches
much so reducing the number of lines is worth it.

-- 
Michal Hocko
SUSE Labs

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[PATCH 0.14] oom detection rework v6 Michal Hocko <mhocko@kernel.org> - 2016-04-20 21:50 +0200
  [PATCH 07/14] mm, compaction: Simplify __alloc_pages_direct_compact feedback interface Michal Hocko <mhocko@kernel.org> - 2016-04-20 21:50 +0200
  [PATCH 03/14] mm, compaction: cover all compaction mode in compact_zone Michal Hocko <mhocko@kernel.org> - 2016-04-20 21:50 +0200
  [PATCH 10/14] mm, oom: rework oom detection Michal Hocko <mhocko@kernel.org> - 2016-04-20 21:50 +0200
  [PATCH 14/14] mm, oom, compaction: prevent from should_compact_retry looping for ever for costly orders Michal Hocko <mhocko@kernel.org> - 2016-04-20 21:50 +0200
    Re: [PATCH 14/14] mm, oom, compaction: prevent from  should_compact_retry looping for ever for costly orders Vlastimil Babka <vbabka@suse.cz> - 2016-04-28 11:00 +0200
      Re: [PATCH 14/14] mm, oom, compaction: prevent from  should_compact_retry looping for ever for costly orders Michal Hocko <mhocko@kernel.org> - 2016-04-28 14:40 +0200
    Re: [PATCH 14/14] mm, oom, compaction: prevent from  should_compact_retry looping for ever for costly orders Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-05-04 08:30 +0200
      Re: [PATCH 14/14] mm, oom, compaction: prevent from  should_compact_retry looping for ever for costly orders Michal Hocko <mhocko@kernel.org> - 2016-05-04 11:10 +0200
        Re: [PATCH 14/14] mm, oom, compaction: prevent from  should_compact_retry looping for ever for costly orders Joonsoo Kim <js1304@gmail.com> - 2016-05-04 17:20 +0200
          Re: [PATCH 14/14] mm, oom, compaction: prevent from  should_compact_retry looping for ever for costly orders Michal Hocko <mhocko@kernel.org> - 2016-05-04 21:30 +0200
  [PATCH 11/14] mm: throttle on IO only when there are too many dirty and writeback pages Michal Hocko <mhocko@kernel.org> - 2016-04-20 21:50 +0200
  [PATCH 12/14] mm, oom: protect !costly allocations some more Michal Hocko <mhocko@kernel.org> - 2016-04-20 21:50 +0200
    Re: [PATCH 12/14] mm, oom: protect !costly allocations some more Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-05-04 08:10 +0200
      Re: [PATCH 12/14] mm, oom: protect !costly allocations some more Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-05-04 08:40 +0200
        Re: [PATCH 12/14] mm, oom: protect !costly allocations some more Michal Hocko <mhocko@kernel.org> - 2016-05-04 11:00 +0200
          Re: [PATCH 12/14] mm, oom: protect !costly allocations some more Joonsoo Kim <js1304@gmail.com> - 2016-05-04 17:00 +0200
            Re: [PATCH 12/14] mm, oom: protect !costly allocations some more Michal Hocko <mhocko@kernel.org> - 2016-05-04 20:20 +0200
      Re: [PATCH 12/14] mm, oom: protect !costly allocations some more Michal Hocko <mhocko@kernel.org> - 2016-05-04 11:00 +0200
        Re: [PATCH 12/14] mm, oom: protect !costly allocations some more Joonsoo Kim <js1304@gmail.com> - 2016-05-04 16:40 +0200
          Re: [PATCH 12/14] mm, oom: protect !costly allocations some more Michal Hocko <mhocko@kernel.org> - 2016-05-04 20:30 +0200
  [PATCH 01/14] vmscan: consider classzone_idx in compaction_ready Michal Hocko <mhocko@kernel.org> - 2016-04-20 21:50 +0200
    Re: [PATCH 01/14] vmscan: consider classzone_idx in compaction_ready "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2016-04-21 06:40 +0200
    Re: [PATCH 01/14] vmscan: consider classzone_idx in compaction_ready Michal Hocko <mhocko@kernel.org> - 2016-05-04 16:00 +0200
  [PATCH 05/14] mm, compaction: distinguish between full and partial COMPACT_COMPLETE Michal Hocko <mhocko@kernel.org> - 2016-04-20 21:50 +0200
    Re: [PATCH 05/14] mm, compaction: distinguish between full and partial COMPACT_COMPLETE "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2016-04-21 08:40 +0200
  [PATCH 08/14] mm, compaction: Abstract compaction feedback to helpers Michal Hocko <mhocko@kernel.org> - 2016-04-20 21:50 +0200
    Re: [PATCH 08/14] mm, compaction: Abstract compaction feedback to  helpers Vlastimil Babka <vbabka@suse.cz> - 2016-04-28 10:50 +0200
  [PATCH 09/14] mm: use compaction feedback for thp backoff conditions Michal Hocko <mhocko@kernel.org> - 2016-04-20 21:50 +0200
    Re: [PATCH 09/14] mm: use compaction feedback for thp backoff conditions "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2016-04-21 09:10 +0200
    Re: [PATCH 09/14] mm: use compaction feedback for thp backoff  conditions Vlastimil Babka <vbabka@suse.cz> - 2016-04-28 11:00 +0200
      Re: [PATCH 09/14] mm: use compaction feedback for thp backoff  conditions Michal Hocko <mhocko@kernel.org> - 2016-04-28 14:40 +0200
        Re: [PATCH 09/14] mm: use compaction feedback for thp backoff  conditions Vlastimil Babka <vbabka@suse.cz> - 2016-04-29 11:20 +0200
          Re: [PATCH 09/14] mm: use compaction feedback for thp backoff  conditions Michal Hocko <mhocko@kernel.org> - 2016-04-29 11:30 +0200
  [PATCH 13/14] mm: consider compaction feedback also for costly allocation Michal Hocko <mhocko@kernel.org> - 2016-04-20 21:50 +0200
  [PATCH 04/14] mm, compaction: distinguish COMPACT_DEFERRED from COMPACT_SKIPPED Michal Hocko <mhocko@kernel.org> - 2016-04-20 22:00 +0200
  [PATCH 02/14] mm, compaction: change COMPACT_ constants into enum Michal Hocko <mhocko@kernel.org> - 2016-04-20 22:00 +0200
  Re: [PATCH 0.14] oom detection rework v6 Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-05-04 07:50 +0200
    Re: [PATCH 0.14] oom detection rework v6 Vlastimil Babka <vbabka@suse.cz> - 2016-05-04 10:20 +0200
      Re: [PATCH 0.14] oom detection rework v6 Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-05-04 10:40 +0200
      Re: [PATCH 0.14] oom detection rework v6 Michal Hocko <mhocko@kernel.org> - 2016-05-04 11:00 +0200
    Re: [PATCH 0.14] oom detection rework v6 Michal Hocko <mhocko@kernel.org> - 2016-05-04 10:50 +0200
      Re: [PATCH 0.14] oom detection rework v6 Joonsoo Kim <js1304@gmail.com> - 2016-05-04 16:40 +0200
        Re: [PATCH 0.14] oom detection rework v6 Michal Hocko <mhocko@kernel.org> - 2016-05-04 20:20 +0200
          Re: [PATCH 0.14] oom detection rework v6 Joonsoo Kim <js1304@gmail.com> - 2016-05-10 08:50 +0200
            Re: [PATCH 0.14] oom detection rework v6 Vlastimil Babka <vbabka@suse.cz> - 2016-05-10 09:10 +0200
              Re: [PATCH 0.14] oom detection rework v6 Joonsoo Kim <js1304@gmail.com> - 2016-05-10 10:10 +0200
                Re: [PATCH 0.14] oom detection rework v6 Michal Hocko <mhocko@kernel.org> - 2016-05-10 11:50 +0200
            Re: [PATCH 0.14] oom detection rework v6 Michal Hocko <mhocko@kernel.org> - 2016-05-10 11:50 +0200
              Re: [PATCH 0.14] oom detection rework v6 Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-05-12 04:30 +0200
                Re: [PATCH 0.14] oom detection rework v6 Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-05-12 07:20 +0200
                Re: [PATCH 0.14] oom detection rework v6 Michal Hocko <mhocko@kernel.org> - 2016-05-12 13:10 +0200

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