linux-kernel - Re: [RFC][PATCH v3] slub: Keep page and object in sync in slab_alloc

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Message-ID: <0000013c5ac3b6c6-3f8fa112-f11b-4b13-8394-7f688fd18191-000000@email.amazonses.com>
Date:	Mon, 21 Jan 2013 01:40:41 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	RT <linux-rt-users@...r.kernel.org>,
	Clark Williams <clark@...hat.com>,
	John Kacur <jkacur@...il.com>,
	"Luis Claudio R. Goncalves" <lgoncalv@...hat.com>
Subject: Re: [RFC][PATCH v3] slub: Keep page and object in sync in
 slab_alloc_node()

On Fri, 18 Jan 2013, Eric Dumazet wrote:

> On Fri, 2013-01-18 at 18:40 +0000, Christoph Lameter wrote:
>
> > The fetching of the tid is the only critical thing here. If the tid is
> > retrieved from the right cpu then the cmpxchg will fail if any changes
> > occured to freelist or the page variable.
> >
> > The tid can be retrieved without disabling preemption through
> > this_cpu_read().
>
> Strictly speaking, this_cpu_read() _does_ disable preemption.

Yes on x86 the relocation and the fetch is just a single instruction and
therefore no preemption can occur.

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