linux-kernel - Re: lockdep complaints in slab allocator

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Message-ID: <1259098552.4531.1857.camel@laptop>
Date:	Tue, 24 Nov 2009 22:35:52 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Matt Mackall <mpm@...enic.com>, paulmck@...ux.vnet.ibm.com,
	Pekka Enberg <penberg@...helsinki.fi>, linux-mm@...ck.org,
	Christoph Lameter <cl@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: lockdep complaints in slab allocator

On Tue, 2009-11-24 at 13:22 -0800, David Rientjes wrote:
> On Tue, 24 Nov 2009, Peter Zijlstra wrote:
> 
> > > slqb still has a 5-10% performance regression compared to slab for 
> > > benchmarks such as netperf TCP_RR on machines with high cpu counts, 
> > > forcing that type of regression isn't acceptable.
> > 
> > Having _4_ slab allocators is equally unacceptable.
> > 
> 
> So you just advocated to merging slqb so that it gets more testing and 
> development, and then use its inclusion in a statistic to say we should 
> remove others solely because the space is too cluttered?

We should cull something, just merging more and more of them is useless
and wastes everybody's time since you have to add features and
interfaces to all of them.

> We use slab partially because the regression in slub was too severe for 
> some of our benchmarks, and while CONFIG_SLUB may be the kernel default 
> there are still distros that use slab as the default as well.  We cannot 
> simply remove an allocator that is superior to others because it is old or 
> has increased complexity.

Then maybe we should toss SLUB? But then there's people who say SLUB is
better for them. Without forcing something to happen we'll be stuck with
multiple allocators forever.


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