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Date: Wed, 1 Jul 2009 01:31:06 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux-foundation.org>,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       x86@kernel.org, linux-arch@vger.kernel.org, andi@firstfloor.org,
       hpa@zytor.com, tglx@linutronix.de
Subject: Re: [PATCHSET] percpu: generalize first chunk allocators and
	improve lpage NUMA support
Message-ID: <20090630233106.GB28830@elte.hu>
References: <1245850216-31653-1-git-send-email-tj@kernel.org> <20090624165508.30b88343.akpm@linux-foundation.org> <alpine.DEB.1.10.0906291920100.32637@gentwo.org> <20090629163937.94c8cedd.akpm@linux-foundation.org> <20090630191517.GB20567@elte.hu> <alpine.DEB.1.10.0906301533400.29795@gentwo.org> <20090630213146.GA17492@elte.hu> <alpine.DEB.1.10.0906301809330.11362@gentwo.org> <4A4A9DC6.6020003@kernel.org>
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* Tejun Heo <tj@kernel.org> wrote:

> Hello, Christoph.
> 
> Christoph Lameter wrote:

> > I looked at allocating for online cpus only a couple of years 
> > back but at that per cpu state was kept for offlined cpus in per 
> > cpu areas. There are numerous assumptions in per cpu handling 
> > all over the kernel that a percpu area is always available.
> 
> The plan is to allocate and keep percpu areas for cpus which have 
> ever been up.  There'll be no taking down of percpu areas.  
> Conversion from possible to has_ever_been_up should be much easier 
> than possible -> online.  State keeping will work fine too.

That sounds like a very sane plan.

	Ingo