From: Mel Gorman <mgorman@suse.de>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linuxfoundation.org>,
Rik van Riel <riel@redhat.com>,
David Rientjes <rientjes@google.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Fengguang Wu <fengguang.wu@intel.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: page_alloc: Default to node-ordering on 64-bit NUMA machines
Date: Fri, 5 Sep 2014 11:30:42 +0100 [thread overview]
Message-ID: <20140905103041.GH17501@suse.de> (raw)
In-Reply-To: <20140904152915.GB10794@cmpxchg.org>
On Thu, Sep 04, 2014 at 11:29:29AM -0400, Johannes Weiner wrote:
> On Tue, Sep 02, 2014 at 04:21:43PM +0100, Mel Gorman wrote:
> > On Tue, Sep 02, 2014 at 09:51:20AM -0400, Johannes Weiner wrote:
> > > On Mon, Sep 01, 2014 at 01:55:51PM +0100, Mel Gorman wrote:
> > > > I cannot find a good reason to incur a performance penalty on all 64-bit NUMA
> > > > machines in case someone throws a brain damanged TV or graphics card in there.
> > > > This patch defaults to node-ordering on 64-bit NUMA machines. I was tempted
> > > > to make it default everywhere but I understand that some embedded arches may
> > > > be using 32-bit NUMA where I cannot predict the consequences.
> > >
> > > This patch is a step in the right direction, but I'm not too fond of
> > > further fragmenting this code and where it applies, while leaving all
> > > the complexity from the heuristics and the zonelist building in, just
> > > on spec. Could we at least remove the heuristics too? If anybody is
> > > affected by this, they can always override the default on the cmdline.
> >
> > I see no problem with deleting the heuristics. Default node for 64-bit
> > and default zone for 32-bit sound ok to you?
>
> Is there a strong reason against defaulting both to node order? Zone
> ordering, if anything, is a niche application. We might even be able
> to remove it in the future. We still have the backup of allowing the
> user to explicitely request zone ordering on the commandline, should
> someone depend on it unexpectedly.
Low memory depletion is the reason to default to zone order on 32-bit
NUMA. If processes on node 0 deplete the Normal zone from normal
activity then other nodes must keep reclaiming from Normal for all kernel
allocations. The problem is worse if CONFIG_HIGHPTE is not set.
A default of node-ordering on 32-bit NUMA increases low memory pressure
leading to increased reclaim and potentially easier to trigger OOM. I
expect this problem was worse in the past when the normal zone could be
filled with dirty pages under writeback. However low memory pressure is
still enough of a concern that I'm wary of changing the default of 32-bit
NUMA without knowing who even cares about 32-bit NUMA.
--
Mel Gorman
SUSE Labs
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next prev parent reply other threads:[~2014-09-05 10:30 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-01 12:55 [PATCH] mm: page_alloc: Default to node-ordering on 64-bit NUMA machines Mel Gorman
2014-09-02 1:12 ` Kamezawa Hiroyuki
2014-09-02 13:51 ` Johannes Weiner
2014-09-02 14:01 ` Kamezawa Hiroyuki
2014-09-02 15:21 ` Mel Gorman
2014-09-04 15:29 ` Johannes Weiner
2014-09-05 10:30 ` Mel Gorman [this message]
2014-09-09 14:46 ` [PATCH] mm: page_alloc: Default node-ordering on 64-bit NUMA, zone-ordering on 32-bit v2 Mel Gorman
2014-09-09 14:52 ` Johannes Weiner
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