From: Mel Gorman <mgorman@suse.de>
To: riel@redhat.com
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
peterz@infradead.org, mingo@redhat.com, chegu_vinod@hp.com
Subject: Re: [PATCH 1/6] numa,sched,mm: remove p->numa_migrate_deferred
Date: Tue, 21 Jan 2014 11:52:23 +0000 [thread overview]
Message-ID: <20140121115223.GF4963@suse.de> (raw)
In-Reply-To: <1390245667-24193-2-git-send-email-riel@redhat.com>
On Mon, Jan 20, 2014 at 02:21:02PM -0500, riel@redhat.com wrote:
> From: Rik van Riel <riel@redhat.com>
>
> Excessive migration of pages can hurt the performance of workloads
> that span multiple NUMA nodes. However, it turns out that the
> p->numa_migrate_deferred knob is a really big hammer, which does
> reduce migration rates, but does not actually help performance.
>
> Now that the second stage of the automatic numa balancing code
> has stabilized, it is time to replace the simplistic migration
> deferral code with something smarter.
>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Chegu Vinod <chegu_vinod@hp.com>
> Signed-off-by: Rik van Riel <riel@redhat.com>
When I added a tracepoint to track deferred migration I was surprised how
often it triggered for some workloads. I agree that we want to do something
better because it was a crutch albeit a necessary one at the time.
Note that the knob was not about performance as such, it was about avoiding
worst-case behaviour. We should keep an eye out for bugs that look like
excessive migration on workloads that are not converging. Reintroducing this
hammer would be a last resort for working around the problem.
Finally, the sysctl is documented in Documentation/sysctl/kernel.txt and
this patch should also remove it.
Functionally, the patch looks fine and it's time to reinvestigate if
it's necessary so assuming the documentation gets removed;
Acked-by: Mel Gorman <mgorman@suse.de>
--
Mel Gorman
SUSE Labs
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next prev parent reply other threads:[~2014-01-21 11:52 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-20 19:21 [PATCH v3 0/6] pseudo-interleaving for automatic NUMA balancing riel
2014-01-20 19:21 ` [PATCH 1/6] numa,sched,mm: remove p->numa_migrate_deferred riel
2014-01-21 11:52 ` Mel Gorman [this message]
2014-01-20 19:21 ` [PATCH 2/6] numa,sched: track from which nodes NUMA faults are triggered riel
2014-01-21 12:21 ` Mel Gorman
2014-01-21 22:26 ` Rik van Riel
2014-01-24 14:14 ` Mel Gorman
2014-01-20 19:21 ` [PATCH 3/6] numa,sched: build per numa_group active node mask from faults_from statistics riel
2014-01-21 14:19 ` Mel Gorman
2014-01-21 15:09 ` Rik van Riel
2014-01-21 15:41 ` Mel Gorman
2014-01-20 19:21 ` [PATCH 4/6] numa,sched,mm: use active_nodes nodemask to limit numa migrations riel
2014-01-21 15:08 ` Mel Gorman
2014-01-20 19:21 ` [PATCH 5/6] numa,sched: normalize faults_from stats and weigh by CPU use riel
2014-01-21 15:56 ` Mel Gorman
2014-01-21 21:05 ` Rik van Riel
2014-01-20 19:21 ` [PATCH 6/6] numa,sched: do statistics calculation using local variables only riel
2014-01-21 16:15 ` Mel Gorman
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