linux-kernel - Re: [PATCH -mm] slub: fix cpu hotplug offline/online path

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Message-ID: <Pine.LNX.4.64.0710111036090.31811@schroedinger.engr.sgi.com>
Date:	Thu, 11 Oct 2007 10:36:52 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Akinobu Mita <akinobu.mita@...il.com>
cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH -mm] slub: fix cpu hotplug offline/online path

On Fri, 12 Oct 2007, Akinobu Mita wrote:

> > > This means get_cpu_slab() always return NULL when CPU is being onlined.
> > > So I can't use get_cpu_slab to check whether kmem_cache_cpu_free
> > > initalization for the CPU has already been done or not.
> >
> > If you have set it to NULL then the earlier kmem_cache_cpu structures has
> > been freed. Why is it a problem to allocate another one when the cpu comes
> > up again?
> >
> 
> kmem_cache_cpu_free per-cpu singly list will be broken by calling
> init_alloc_cpu_cpu() twice. It happens when online/offlining CPU.
> All three patches I send attempt to make init_alloc_cpu_cpu()
> called only once for each cpu.

Ahhh.. Its the initialization of the kmem_cache_cpu pool that is the issue 
not the allocation of the kmem_cache_cpu() structure.

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