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

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Date:	Tue, 16 Oct 2012 15:36:44 -0300
From:	Ezequiel Garcia <elezegarcia@...il.com>
To:	Tim Bird <tim.bird@...sony.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"celinux-dev@...ts.celinuxforum.org" 
	<celinux-dev@...ts.celinuxforum.org>
Subject: Re: [Q] Default SLAB allocator

On Tue, Oct 16, 2012 at 3:07 PM, Tim Bird <tim.bird@...sony.com> wrote:
> On 10/16/2012 05:56 AM, Eric Dumazet wrote:
>> On Tue, 2012-10-16 at 09:35 -0300, Ezequiel Garcia wrote:
>>
>>> Now, returning to the fragmentation. The problem with SLAB is that
>>> its smaller cache available for kmalloced objects is 32 bytes;
>>> while SLUB allows 8, 16, 24 ...
>>>
>>> Perhaps adding smaller caches to SLAB might make sense?
>>> Is there any strong reason for NOT doing this?
>>
>> I would remove small kmalloc-XX caches, as sharing a cache line
>> is sometime dangerous for performance, because of false sharing.
>>
>> They make sense only for very small hosts.
>
> That's interesting...
>
> It would be good to measure the performance/size tradeoff here.
> I'm interested in very small systems, and it might be worth
> the tradeoff, depending on how bad the performance is.  Maybe
> a new config option would be useful (I can hear the groans now... :-)
>

It might be worth reminding that very small systems can use SLOB
allocator, which does not suffer from this kind of fragmentation.

    Ezequiel
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