linux-kernel - Re: [PATCH 0/3] FUTEX : new PRIVATE futexes, SMP and NUMA improvements

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Message-Id: <200703161130.06669.dada1@cosmosbay.com>
Date:	Fri, 16 Mar 2007 11:30:06 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Ulrich Drepper <drepper@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...e.de>,
	Ravikiran G Thirumalai <kiran@...lex86.org>,
	"Shai Fultheim (Shai@...lex86.org)" <shai@...lex86.org>,
	pravin b shelar <pravin.shelar@...softinc.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] FUTEX : new PRIVATE futexes, SMP and NUMA improvements

On Friday 16 March 2007 11:10, Peter Zijlstra wrote:

> http://programming.kicks-ass.net/kernel-patches/futex-vma-cache/vma_cache.p
>atch

Oh thanks

>
> > But if it has to walk the vmas (and take mmap_sem), you already loose the
> > PRIVATE benefit.
>
> It doesn't take mmap_sem, I am aware of the problems.

Yes but the vma_anon() -> vma_cache_find() needs to read 3 cache lines on 
x86_64 (sizeof(struct vma_cache) = 136)
and dirty one bit, so it might be more expensive than the mmap_sem ...

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