linux-kernel - Re: [Q] Default SLAB allocator

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Message-ID: <alpine.DEB.2.00.1210130252030.7462@chino.kir.corp.google.com>
Date:	Sat, 13 Oct 2012 02:54:49 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Ezequiel Garcia <elezegarcia@...il.com>
cc:	Andi Kleen <andi@...stfloor.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Tim Bird <tim.bird@...sony.com>,
	celinux-dev@...ts.celinuxforum.org
Subject: Re: [Q] Default SLAB allocator

On Fri, 12 Oct 2012, Ezequiel Garcia wrote:

> >> SLUB is a non-starter for us and incurs a >10% performance degradation in
> >> netperf TCP_RR.
> >
> 
> Where are you seeing that?
> 

In my benchmarking results.

> Notice that many defconfigs are for embedded devices,
> and many of them say "use SLAB"; I wonder if that's right.
> 

If a device doesn't require the smallest memory footprint possible (SLOB) 
then SLAB is the right choice when there's a limited amount of memory; 
SLUB requires higher order pages for the best performance (on my desktop 
system running with CONFIG_SLUB, over 50% of the slab caches default to be 
high order).

> Is there any intention to replace SLAB by SLUB?

There may be an intent, but it'll be nacked as long as there's a 
performance degradation.

> In that case it could make sense to change defconfigs, although
> it wouldn't be based on any actual tests.
> 

Um, you can't just go changing defconfigs without doing some due diligence 
in ensuring it won't be deterimental for those users.
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