linux-kernel - Re: [rfc] SLOB memory ordering issue

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Date:	Wed, 15 Oct 2008 11:29:32 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
cc:	Matt Mackall <mpm@...enic.com>,
	Pekka Enberg <penberg@...helsinki.fi>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [rfc] SLOB memory ordering issue

On Thu, 16 Oct 2008, Nick Piggin wrote:
> 
> When I said "I'd really hate to add a branch to the slab fastpath", it
> wasn't a tacit acknowlegement that the barrier is the only way to go,
> if it sounded that way.
> 
> I meant: I'd *really* hate to add a branch to the slab fastpath :)

Well, quite frankly, your choice of subject line and whole point of 
argument may have confused me.

You started out - and continue to - make this sound like it's a 
SLAB/SLOB/SLUB issue. It's not. 

I agree there is quite likely memory ordering issues - possibly old ones, 
but quite possibly also ones that have just happened fairly recently as 
we've done more unlocked lookups - and all I've ever disagreed with is 
how you seem to have mixed this up with the allocator.

And I still don't understand why you even _mention_ the slab fastpath. It 
seems totally immaterial.

			Linus
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