Re: [patch 1/2] mm, compaction: kcompactd should not ignore pageblock skip

From	David Rientjes <rientjes@google.com>
Newsgroups	linux.kernel
Subject	Re: [patch 1/2] mm, compaction: kcompactd should not ignore pageblock skip
Date	2017-09-11 23:20 +0200
Message-ID	<uoEhC-hu-49@gated-at.bofh.it> (permalink)
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On Mon, 11 Sep 2017, Vlastimil Babka wrote:

> > A follow-up change will set the pageblock skip for this memory since it is 
> > never useful for either scanner.
> > """
> > 
> >> Also there's now a danger that in cases where there's no direct
> >> compaction happening (just kcompactd), nothing will ever call
> >> __reset_isolation_suitable().
> >>
> > 
> > I'm not sure that is helpful in a context where no high-order memory can 
> > call direct compaction that kcompactd needlessly scanning the same memory 
> > over and over is beneficial.
> 
> The point is that if it becomes beneficial again, we won't know as there
> will be still be skip bits.
> 

Why is kcompactd_do_work() not sometimes doing 
__reset_isolation_suitable() in the first place, if only to reset the 
per-zone migration and freeing scanner cached pfns?  It seems fragile to 
rely on other threads doing direct compaction to reset the per-zone state 
of compaction.

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Re: [patch 1/2] mm, compaction: kcompactd should not ignore pageblock  skip David Rientjes <rientjes@google.com> - 2017-09-11 03:10 +0200
  Re: [patch 1/2] mm, compaction: kcompactd should not ignore pageblock  skip Vlastimil Babka <vbabka@suse.cz> - 2017-09-11 08:40 +0200
    Re: [patch 1/2] mm, compaction: kcompactd should not ignore pageblock  skip David Rientjes <rientjes@google.com> - 2017-09-11 23:20 +0200

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