linux-kernel - Re: Major regression on hackbench with SLUB

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Message-ID: <Pine.LNX.4.64.0712131410190.25120@schroedinger.engr.sgi.com>
Date:	Thu, 13 Dec 2007 14:11:24 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: Major regression on hackbench with SLUB

On Fri, 7 Dec 2007, Linus Torvalds wrote:

> The biggest cost of __slab_alloc() in my profile is the "slab_lock()", but 
> that may not be the one that causes problems in a 64-cpu setup, so it 
> would be good to have that verified.

Hmmmm.. This would indicate lock contention on a slab.

> [ The whole node match thing is likely totally bogus. I suspect we pay 
>   *more* in trying to match nodes than we'd ever likely pay in just 
>   returning the wrong node for an allocation, but that's neither here nor 
>   there ]

Node match is necessary in order to make the allocator able to get memory 
for the node that the caller requested.
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