linux-kernel - Re: [RFC][PATCH v2] slub: Keep page and object in sync in slab_alloc

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Date:	Mon, 21 Jan 2013 17:11:21 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Christoph Lameter <cl@...ux.com>,
	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 v2] slub: Keep page and object in sync in
 slab_alloc_node()

On Fri, Jan 18, 2013 at 10:55:01AM -0500, Steven Rostedt wrote:
> On Fri, 2013-01-18 at 10:04 -0500, Steven Rostedt wrote:
> 
> Just to be more complete:
> 
> > 	CPU0			CPU1
> > 	----			----
> 			c = __this_cpu_ptr(s->cpu_slab);
> 			<migrates to CPU0>
> 
> > <cpu fetches c->page>
> 			<another task>
> 
> > 			updates c->tid
> > 			updates c->page
> > 			updates c->freelist
> > <cpu fetches c->tid>
> > <cpu fetches c->freelist>
> > 
> >   node_match() succeeds even though
> >     current c->page wont
> > 
> 
>  <migrates back to CPU 1>

Hello.
I have one stupid question just for curiosity.
Does the processor re-order instructions which load data from same cacheline?

> >  this_cpu_cmpxchg_double() only tests
> >    the object (freelist) and tid, both which
> >    will match, but the page that was tested
> >    isn't the right one.
> > 
> 
> Yes, it's very unlikely, but we are in the business of dealing with the
> very unlikely. That's because in our business, the very unlikely is very
> likely. Damn, I need to buy a lotto ticket!
> 
> -- Steve
> 
> 
> --
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