Re: [Q] Default SLAB allocator

From: Ezequiel Garcia
Date: Tue Oct 16 2012 - 14:36:37 EST

On Tue, Oct 16, 2012 at 3:07 PM, Tim Bird <tim.bird@xxxxxxxxxxx> 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.

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