Re: [RFC 12/13] mm, compaction: more reliably increase direct compaction priority

From	Michal Hocko <mhocko@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [RFC 12/13] mm, compaction: more reliably increase direct compaction priority
Date	2016-05-16 12:00 +0200
Message-ID	<rzntE-5j2-9@gated-at.bofh.it> (permalink)
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On Mon 16-05-16 11:27:56, Vlastimil Babka wrote:
> On 05/16/2016 10:14 AM, Michal Hocko wrote:
> > On Mon 16-05-16 09:31:44, Vlastimil Babka wrote:
[...]
> > > Also my understanding of the initial compaction priorities is to lower the
> > > latency if fragmentation is just light and there's enough memory. Once we
> > > start struggling, I don't see much point in not switching to the full
> > > compaction priority quickly.
> > 
> > That is true but why to compact when there are high order pages and they
> > are just hidden by the watermark check.
> 
> Compaction should skip such zone regardless of priority.

The point I've tried to raise is that we shouldn't conflate the purpose
of the two. The reclaim is here primarily to get us over the watermarks
while compaction is here to form high order pages. If we get both
together the distinction is blured which, I believe, will lead to more
complicated code in the end. I might be wrong here of course but let's
try to have compaction as much wmark check free as possible.
-- 
Michal Hocko
SUSE Labs

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Re: [RFC 12/13] mm, compaction: more reliably increase direct  compaction priority Michal Hocko <mhocko@kernel.org> - 2016-05-13 16:20 +0200
  Re: [RFC 12/13] mm, compaction: more reliably increase direct  compaction priority Vlastimil Babka <vbabka@suse.cz> - 2016-05-16 09:40 +0200
    Re: [RFC 12/13] mm, compaction: more reliably increase direct  compaction priority Michal Hocko <mhocko@kernel.org> - 2016-05-16 10:20 +0200
      Re: [RFC 12/13] mm, compaction: more reliably increase direct  compaction priority Vlastimil Babka <vbabka@suse.cz> - 2016-05-16 11:30 +0200
        Re: [RFC 12/13] mm, compaction: more reliably increase direct  compaction priority Michal Hocko <mhocko@kernel.org> - 2016-05-16 12:00 +0200

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