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

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Date:	Sat, 13 Oct 2012 09:44:01 -0300
From:	Ezequiel Garcia <elezegarcia@...il.com>
To:	David Rientjes <rientjes@...gle.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

Hi David,

On Sat, Oct 13, 2012 at 6:54 AM, David Rientjes <rientjes@...gle.com> wrote:
> 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).
>

But SLAB suffers from a lot more internal fragmentation than SLUB,
which I guess is a known fact. So memory-constrained devices
would waste more memory by using SLAB.
I must admit a didn't look at page order (but I will now).


>> 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.

Yeah, it would be very interesting to compare SLABs on at least
some of those platforms.


    Ezequiel
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