From: Wen Congyang <wency@cn.fujitsu.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: David Rientjes <rientjes@google.com>,
Tang Chen <tangchen@cn.fujitsu.com>,
mingo@redhat.com, miaox@cn.fujitsu.com,
linux-kernel@vger.kernel.org, linux-numa@vger.kernel.org
Subject: Re: [PATCH] Do not use cpu_to_node() to find an offlined cpu's node.
Date: Wed, 10 Oct 2012 18:10:09 +0800 [thread overview]
Message-ID: <50754981.80900@cn.fujitsu.com> (raw)
In-Reply-To: <1349862694.7880.114.camel@twins>
At 10/10/2012 05:51 PM, Peter Zijlstra Wrote:
> On Wed, 2012-10-10 at 17:33 +0800, Wen Congyang wrote:
>>
>> Hmm, if per-cpu memory is preserved, and we can't offline and remove
>> this memory. So we can't offline the node.
>>
>> But, if the node is hot added, and per-cpu memory doesn't use the
>> memory on this node. We can hotremove cpu/memory on this node, and then
>> offline this node.
>>
>> Before the cpu is hotadded, cpu's node is -1. We set cpu<->node mapping
>> when it is hotadded. So the entire cpu<->node mapping was not invariant
>> during hotplug.
>>
>> So it is why I try to clear it when the cpu is hot-removed.
>>
>> As we need the mapping to migrate a task to the cpu on the same node first,
>> I think we can clear the mapping when the node is offlined.
>
> Hmm maybe, but hardware that can hot-add is rare and nobody has it so
> nobody cares ;-)
Yes, nobody cares it now. But we have a such hardware, so I care it now.
>
> But by clearing cpu_to_node on every hotplug you change semantics for
> all hardware and everybody gets to feel the pain.
>
> I'm not saying you cannot change things, I'm only saying you should be
> far more careful about it, not change it and wait for things to break.
> Put in some effort to find things that might break and warn people --
> sure, you'll always miss some, and that's ok.
I use ./scripts/get_maintainer.pl, and it doesn't tell me that I should cc
you when I post that patch.
next prev parent reply other threads:[~2012-10-10 10:10 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-08 2:59 [PATCH] Do not use cpu_to_node() to find an offlined cpu's node Tang Chen
2012-10-09 6:21 ` David Rientjes
2012-10-09 8:34 ` Wen Congyang
2012-10-09 8:39 ` Tang Chen
2012-10-09 10:04 ` David Rientjes
2012-10-09 10:22 ` Wen Congyang
2012-10-09 20:00 ` David Rientjes
2012-10-09 10:57 ` Peter Zijlstra
2012-10-09 20:36 ` David Rientjes
2012-10-09 20:47 ` Peter Zijlstra
2012-10-09 23:27 ` David Rientjes
2012-10-10 2:06 ` Wen Congyang
2012-10-10 3:48 ` Wen Congyang
2012-10-10 9:10 ` Peter Zijlstra
2012-10-10 9:33 ` Wen Congyang
2012-10-10 9:51 ` Peter Zijlstra
2012-10-10 10:10 ` Wen Congyang [this message]
2012-10-10 10:07 ` Peter Zijlstra
2012-10-10 20:30 ` David Rientjes
2012-10-10 20:37 ` Andrew Morton
2012-10-10 20:57 ` David Rientjes
2012-10-18 0:52 ` David Rientjes
2012-10-18 2:51 ` Tang Chen
2012-10-18 3:29 ` David Rientjes
2012-10-19 11:18 ` Peter Zijlstra
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