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Re: [RHEL-ALT-7.4 PATCH 2/2] sched,numa: scale scan period with tasks in group and shared/private

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On Mon, Jul 31, 2017 at 03:28:47PM -0400, Rik van Riel wrote:
> From: Rik van Riel <riel@redhat.com>
> 
> Running 80 tasks in the same group, or as threads of the same process,
> results in the memory getting scanned 80x as fast as it would be if a
> single task was using the memory.
> 
> This really hurts some workloads.
> 

It would be nice to specify what workloads in particular and what sort
of machine because I'm willing to bet it has a bigger impact on machines
with 4+ nodes, particularly if they are not fully connected topologies.
Furthermore, I'm willing to bet that there would be small regressions on
2-socket machines but with less time spent scanning and processing
faults even if remote accesses are marginally increased.

Still, on balance, this is preferred behaviour.

> Scale the scan period by the number of tasks in the numa group, and
> the shared / private ratio, so the average rate at which memory in
> the group is scanned corresponds roughly to the rate at which a single
> task would scan its memory.
> 
> Signed-off-by: Rik van Riel <riel@redhat.com>

Acked-by: Mel Gorman <mgorman@suse.de>

-- 
Mel Gorman
SUSE Labs

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[PATCH 0/2] numa,sched: improve performance for multi-threaded workloads riel@redhat.com - 2017-07-31 21:40 +0200
  [RHEL-ALT-7.4 PATCH 1/2] numa,sched: slow down scan rate if shared faults dominate riel@redhat.com - 2017-07-31 21:40 +0200
    Re: [RHEL-ALT-7.4 PATCH 1/2] numa,sched: slow down scan rate if  shared faults dominate Mel Gorman <mgorman@suse.de> - 2017-08-02 09:10 +0200
    [tip:sched/core] sched/numa: Slow down scan rate if shared faults  dominate tip-bot for Rik van Riel <tipbot@zytor.com> - 2017-08-10 14:20 +0200
  [RHEL-ALT-7.4 PATCH 2/2] sched,numa: scale scan period with tasks in group and shared/private riel@redhat.com - 2017-07-31 21:40 +0200
    Re: [RHEL-ALT-7.4 PATCH 2/2] sched,numa: scale scan period with  tasks in group and shared/private Mel Gorman <mgorman@suse.de> - 2017-08-02 12:30 +0200
    [tip:sched/core] sched/numa: Scale scan period with tasks in group  and shared/private tip-bot for Rik van Riel <tipbot@zytor.com> - 2017-08-10 14:30 +0200

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