From: Andrew Morton <akpm@osdl.org>
To: Paul Jackson <pj@sgi.com>
Cc: nathanl@austin.ibm.com, Simon.Derr@bull.net,
linux-kernel@vger.kernel.org, ntl@pobox.com,
y-goto@jp.fujitsu.com, Anton Blanchard <anton@samba.org>,
Dave Hansen <haveblue@us.ibm.com>,
kamezawa.hiroyu@jp.fujitsu.com
Subject: Re: [PATCH] cpuset: hotunplug cpus and mems in all cpusets
Date: Mon, 28 Aug 2006 23:19:17 -0700 [thread overview]
Message-ID: <20060828231917.6f4bb9af.akpm@osdl.org> (raw)
In-Reply-To: <20060829060824.6621.28300.sendpatchset@jackhammer.engr.sgi.com>
On Mon, 28 Aug 2006 23:08:24 -0700
Paul Jackson <pj@sgi.com> wrote:
> The cpuset code handling hot unplug of CPUs or Memory Nodes
> was incorrect - it could remove a CPU or Node from the top
> cpuset, while leaving it still in some child cpusets.
>
> One basic rule of cpusets is that each cpusets cpus and mems
> are subsets of its parents. The cpuset hot unplug code
> violated this rule.
>
> So the cpuset hotunplug handler must walk down the tree,
> removing any removed CPU or Node from all cpusets.
>
> However, it is not allowed to make a cpusets cpus or mems
> become empty. They can only transition from empty to non-empty,
> not back.
>
> So if the last CPU or Node would be removed from a cpuset by
> the above walk, we scan back up the cpuset hierarchy, finding
> the nearest ancestor that still has something online, and copy
> its CPU or Memory placement.
Did you consider failing the hotremove request instead?
next prev parent reply other threads:[~2006-08-29 6:19 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-08-29 6:08 Paul Jackson
2006-08-29 6:19 ` Andrew Morton [this message]
2006-08-29 7:15 ` Paul Jackson
2006-08-31 10:21 ` Paul Jackson
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