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
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
WARNING: multiple messages have this Message-ID (diff)
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
next prev parent reply other threads:[~2014-01-21 11:52 UTC|newest]
Thread overview: 37+ 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 ` riel
2014-01-20 19:21 ` [PATCH 1/6] numa,sched,mm: remove p->numa_migrate_deferred riel
2014-01-20 19:21 ` riel
2014-01-21 11:52 ` Mel Gorman [this message]
2014-01-21 11:52 ` Mel Gorman
2014-01-20 19:21 ` [PATCH 2/6] numa,sched: track from which nodes NUMA faults are triggered riel
2014-01-20 19:21 ` riel
2014-01-21 12:21 ` Mel Gorman
2014-01-21 12:21 ` Mel Gorman
2014-01-21 22:26 ` Rik van Riel
2014-01-21 22:26 ` Rik van Riel
2014-01-24 14:14 ` Mel Gorman
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
2014-01-20 19:21 ` riel
2014-01-21 14:19 ` Mel Gorman
2014-01-21 14:19 ` Mel Gorman
2014-01-21 15:09 ` Rik van Riel
2014-01-21 15:09 ` Rik van Riel
2014-01-21 15:41 ` Mel Gorman
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
2014-01-20 19:21 ` riel
2014-01-21 15:08 ` Mel Gorman
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
2014-01-20 19:21 ` riel
2014-01-21 15:56 ` Mel Gorman
2014-01-21 15:56 ` Mel Gorman
2014-01-21 21:05 ` Rik van Riel
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
2014-01-20 19:21 ` riel
2014-01-21 16:15 ` Mel Gorman
2014-01-21 16:15 ` Mel Gorman
-- strict thread matches above, loose matches on Subject: below --
2014-01-17 6:17 [PATCH 0/6] pseudo-interleaving for automatic NUMA balancing riel
2014-01-17 6:17 ` [PATCH 1/6] numa,sched,mm: remove p->numa_migrate_deferred riel
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20140121115223.GF4963@suse.de \
--to=mgorman@suse.de \
--cc=chegu_vinod@hp.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=riel@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.