From: Mel Gorman <mgorman@suse.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
Ingo Molnar <mingo@kernel.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 05/16] sched: Select a preferred node with the most numa hinting faults
Date: Thu, 11 Jul 2013 13:53:03 +0100 [thread overview]
Message-ID: <20130711125303.GB2355@suse.de> (raw)
In-Reply-To: <20130711112359.GG25631@dyad.programming.kicks-ass.net>
On Thu, Jul 11, 2013 at 01:23:59PM +0200, Peter Zijlstra wrote:
> On Thu, Jul 11, 2013 at 10:46:49AM +0100, Mel Gorman wrote:
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -1593,6 +1593,7 @@ static void __sched_fork(struct task_struct *p)
> > p->numa_scan_seq = p->mm ? p->mm->numa_scan_seq : 0;
> > p->numa_migrate_seq = p->mm ? p->mm->numa_scan_seq - 1 : 0;
> > p->numa_scan_period = sysctl_numa_balancing_scan_delay;
> > + p->numa_preferred_nid = -1;
>
> (1)
>
> > p->numa_work.next = &p->numa_work;
> > p->numa_faults = NULL;
> > #endif /* CONFIG_NUMA_BALANCING */
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 904fd6f..c0bee41 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -793,7 +793,8 @@ unsigned int sysctl_numa_balancing_scan_delay = 1000;
> >
> > static void task_numa_placement(struct task_struct *p)
> > {
> > - int seq;
> > + int seq, nid, max_nid = 0;
>
> Should you not start with max_nid = -1?
>
For consistency, yes.
> > + unsigned long max_faults = 0;
> >
> > if (!p->mm) /* for example, ksmd faulting in a user's mm */
> > return;
> > @@ -802,7 +803,19 @@ static void task_numa_placement(struct task_struct *p)
> > return;
> > p->numa_scan_seq = seq;
> >
> > - /* FIXME: Scheduling placement policy hints go here */
> > + /* Find the node with the highest number of faults */
> > + for (nid = 0; nid < nr_node_ids; nid++) {
> > + unsigned long faults = p->numa_faults[nid];
> > + p->numa_faults[nid] >>= 1;
> > + if (faults > max_faults) {
> > + max_faults = faults;
> > + max_nid = nid;
> > + }
> > + }
> > +
>
> It is rather unlikely; but suppose the entire ->numa_faults[] array is 0, you'd
> somehow end up selecting max_nid := 0. Which seems inconsistent with \1.
>
This happens more often than you might imagine due to THP false sharing
getting count as shared. If the entire numa_faults[] array is 0 then
max_faults == 0 and it will not update preferred_nid due to the
"max_faults" check below.
> > + /* Update the tasks preferred node if necessary */
> > + if (max_faults && max_nid != p->numa_preferred_nid)
> > + p->numa_preferred_nid = max_nid;
> > }
> >
--
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>
next prev parent reply other threads:[~2013-07-11 12:53 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-11 9:46 [PATCH 0/16] Basic scheduler support for automatic NUMA balancing V4 Mel Gorman
2013-07-11 9:46 ` [PATCH 01/16] mm: numa: Document automatic NUMA balancing sysctls Mel Gorman
2013-07-11 9:46 ` [PATCH 02/16] sched: Track NUMA hinting faults on per-node basis Mel Gorman
2013-07-11 9:46 ` [PATCH 03/16] mm: numa: Account for THP numa hinting faults on the correct node Mel Gorman
2013-07-11 9:46 ` [PATCH 04/16] mm: numa: Do not migrate or account for hinting faults on the zero page Mel Gorman
2013-07-11 11:21 ` Peter Zijlstra
2013-07-11 12:42 ` Mel Gorman
2013-07-11 9:46 ` [PATCH 05/16] sched: Select a preferred node with the most numa hinting faults Mel Gorman
2013-07-11 11:23 ` Peter Zijlstra
2013-07-11 12:53 ` Mel Gorman [this message]
2013-07-11 9:46 ` [PATCH 06/16] sched: Update NUMA hinting faults once per scan Mel Gorman
2013-07-11 9:46 ` [PATCH 07/16] sched: Favour moving tasks towards the preferred node Mel Gorman
2013-07-11 9:46 ` [PATCH 08/16] sched: Reschedule task on preferred NUMA node once selected Mel Gorman
2013-07-11 12:30 ` Peter Zijlstra
2013-07-11 13:03 ` Mel Gorman
2013-07-11 13:11 ` Peter Zijlstra
2013-07-11 14:09 ` Mel Gorman
2013-07-12 10:14 ` Peter Zijlstra
2013-07-12 10:28 ` Mel Gorman
2013-07-11 9:46 ` [PATCH 09/16] sched: Add infrastructure for split shared/private accounting of NUMA hinting faults Mel Gorman
2013-07-11 9:46 ` [PATCH 10/16] sched: Increase NUMA PTE scanning when a new preferred node is selected Mel Gorman
2013-07-11 9:46 ` [PATCH 11/16] sched: Check current->mm before allocating NUMA faults Mel Gorman
2013-07-11 9:46 ` [PATCH 12/16] sched: Set the scan rate proportional to the size of the task being scanned Mel Gorman
2013-07-11 9:46 ` [PATCH 13/16] mm: numa: Scan pages with elevated page_mapcount Mel Gorman
2013-07-11 9:46 ` [PATCH 14/16] sched: Remove check that skips small VMAs Mel Gorman
2013-07-11 9:46 ` [PATCH 15/16] sched: Set preferred NUMA node based on number of private faults Mel Gorman
2013-07-11 9:47 ` [PATCH 16/16] sched: Select least loaded CPU on preferred NUMA node Mel Gorman
2013-07-11 12:39 ` Peter Zijlstra
2013-07-11 13:24 ` Mel Gorman
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=20130711125303.GB2355@suse.de \
--to=mgorman@suse.de \
--cc=aarcange@redhat.com \
--cc=hannes@cmpxchg.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=srikar@linux.vnet.ibm.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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox