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Re: [RFC 4/4] mm, page_alloc: disallow migratetype fallback in fastpath

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On Thu, Sep 29, 2016 at 11:05:48PM +0200, Vlastimil Babka wrote:
> The previous patch has adjusted async compaction so that it helps against
> longterm fragmentation when compacting for a non-MOVABLE high-order allocation.
> The goal of this patch is to force such allocations go through compaction
> once before being allowed to fallback to a pageblock of different migratetype
> (e.g. MOVABLE). In contexts where compaction is not allowed (and for order-0
> allocations), this delayed fallback possibility can still help by trying a
> different zone where fallback might not be needed and potentially waking up
> kswapd earlier.

Hmm... can we justify this compaction overhead in case of that there is
high order freepages in other migratetype pageblock? There is no guarantee
that longterm fragmentation happens and it affects the system
peformance.

And, it would easilly fail to compact in unmovable pageblock since
there would not be migratable pages if everything works as our
intended. So, I guess that checking it over and over doesn't help to
reduce fragmentation and just increase latency of allocation.

Thanks.

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Thread

Regression in mobility grouping? Johannes Weiner <hannes@cmpxchg.org> - 2016-09-28 03:50 +0200
  Re: Regression in mobility grouping? Vlastimil Babka <vbabka@suse.cz> - 2016-09-28 11:10 +0200
    Re: Regression in mobility grouping? Johannes Weiner <hannes@cmpxchg.org> - 2016-09-28 17:50 +0200
      Re: Regression in mobility grouping? Johannes Weiner <hannes@cmpxchg.org> - 2016-09-29 04:30 +0200
        Re: Regression in mobility grouping? Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-09-29 08:10 +0200
          Re: Regression in mobility grouping? Johannes Weiner <hannes@cmpxchg.org> - 2016-09-29 18:20 +0200
            Re: Regression in mobility grouping? Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-10-13 09:40 +0200
        Re: Regression in mobility grouping? Vlastimil Babka <vbabka@suse.cz> - 2016-09-29 09:20 +0200
  Re: Regression in mobility grouping? Mel Gorman <mgorman@suse.de> - 2016-09-28 12:30 +0200
    Re: Regression in mobility grouping? Johannes Weiner <hannes@cmpxchg.org> - 2016-09-28 18:50 +0200
  [RFC 2/4] mm, compaction: add migratetype to compact_control Vlastimil Babka <vbabka@suse.cz> - 2016-09-29 23:10 +0200
  [RFC 1/4] mm, compaction: change migrate_async_suitable() to suitable_migration_source() Vlastimil Babka <vbabka@suse.cz> - 2016-09-29 23:10 +0200
  [RFC 3/4] mm, compaction: restrict async compaction to matching migratetype Vlastimil Babka <vbabka@suse.cz> - 2016-09-29 23:10 +0200
  [RFC 4/4] mm, page_alloc: disallow migratetype fallback in fastpath Vlastimil Babka <vbabka@suse.cz> - 2016-09-29 23:10 +0200
    Re: [RFC 4/4] mm, page_alloc: disallow migratetype fallback in  fastpath Vlastimil Babka <vbabka@suse.cz> - 2016-10-12 17:20 +0200
    Re: [RFC 4/4] mm, page_alloc: disallow migratetype fallback in  fastpath Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-10-13 10:00 +0200
      Re: [RFC 4/4] mm, page_alloc: disallow migratetype fallback in  fastpath Vlastimil Babka <vbabka@suse.cz> - 2016-10-13 13:50 +0200
  [RFC 0/4] try to reduce fragmenting fallbacks Vlastimil Babka <vbabka@suse.cz> - 2016-09-29 23:10 +0200
    [RFC 5/4] mm, page_alloc: split smallest stolen page in fallback Vlastimil Babka <vbabka@suse.cz> - 2016-10-07 10:40 +0200
    Re: [RFC 0/4] try to reduce fragmenting fallbacks Johannes Weiner <hannes@cmpxchg.org> - 2016-10-10 19:30 +0200
    [RFC 6/4] mm, page_alloc: introduce MIGRATE_MIXED migratetype Vlastimil Babka <vbabka@suse.cz> - 2016-10-11 15:20 +0200
    [RFC 7/4] mm, page_alloc: count movable pages when stealing Vlastimil Babka <vbabka@suse.cz> - 2016-10-13 16:20 +0200

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