Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1579612

Re: [PATCH v2 07/10] mm, compaction: restrict async compaction to pageblocks of same migratetype

Show all headers | View raw

On Fri, Feb 10, 2017 at 06:23:40PM +0100, Vlastimil Babka wrote:
> The migrate scanner in async compaction is currently limited to MIGRATE_MOVABLE
> pageblocks. This is a heuristic intended to reduce latency, based on the
> assumption that non-MOVABLE pageblocks are unlikely to contain movable pages.
> 
> However, with the exception of THP's, most high-order allocations are not
> movable. Should the async compaction succeed, this increases the chance that
> the non-MOVABLE allocations will fallback to a MOVABLE pageblock, making the
> long-term fragmentation worse.
> 
> This patch attempts to help the situation by changing async direct compaction
> so that the migrate scanner only scans the pageblocks of the requested
> migratetype. If it's a non-MOVABLE type and there are such pageblocks that do
> contain movable pages, chances are that the allocation can succeed within one
> of such pageblocks, removing the need for a fallback. If that fails, the
> subsequent sync attempt will ignore this restriction.
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Ok, I really like this idea. The thinking of async originally was to
reduce latency but that was also at the time when THP allocations were
stalling for long periods of time. Now that the default has changed,
this idea makes a lot of sense. A few months ago I would have thought
that this will increase the changes that a high-order allocation for the
stack may have a higher chance of failing but with VMAP_STACK, this is
much less of a concern. It would be very nice to know for this patch if
the number of times the extfrag tracepoint is triggered is reduced or
increased by this patch. Do you have that data?

-- 
Mel Gorman
SUSE Labs

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH v2 07/10] mm, compaction: restrict async compaction to pageblocks of same migratetype Vlastimil Babka <vbabka@suse.cz> - 2017-02-10 19:20 +0100
  Re: [PATCH v2 07/10] mm, compaction: restrict async compaction to  pageblocks of same migratetype Mel Gorman <mgorman@techsingularity.net> - 2017-02-13 12:00 +0100
  Re: [PATCH v2 07/10] mm, compaction: restrict async compaction to  pageblocks of same migratetype Johannes Weiner <hannes@cmpxchg.org> - 2017-02-14 21:20 +0100
    Re: [PATCH v2 07/10] mm, compaction: restrict async compaction to  pageblocks of same migratetype Vlastimil Babka <vbabka@suse.cz> - 2017-02-17 17:40 +0100
      Re: [PATCH v2 07/10] mm, compaction: restrict async compaction to  pageblocks of same migratetype Johannes Weiner <hannes@cmpxchg.org> - 2017-02-17 19:30 +0100

csiph-web