Re: [Q] Default SLAB allocator
From: Ezequiel Garcia
Date: Wed Oct 17 2012 - 17:05:14 EST
On Wed, Oct 17, 2012 at 5:58 PM, Tim Bird <tim.bird@xxxxxxxxxxx> wrote:
> On 10/17/2012 12:13 PM, Eric Dumazet wrote:
>> On Wed, 2012-10-17 at 11:45 -0700, Tim Bird wrote:
>>> 8G is a small web server? The RAM budget for Linux on one of
>>> Sony's cameras was 10M. We're not merely not in the same ballpark -
>>> you're in a ballpark and I'm trimming bonsai trees... :-)
>> Even laptops in 2012 have +4GB of ram.
>> (Maybe not Sony laptops, I have to double check ?)
>> Yes, servers do have more ram than laptops.
>> (Maybe not Sony servers, I have to double check ?)
> I wouldn't know. I suspect they are running 4GB+
> like everyone else.
>>>> # grep Slab /proc/meminfo
>>>> Slab: 351592 kB
>>>> # egrep "kmalloc-32|kmalloc-16|kmalloc-8" /proc/slabinfo
>>>> kmalloc-32 11332 12544 32 128 1 : tunables 0 0 0 : slabdata 98 98 0
>>>> kmalloc-16 5888 5888 16 256 1 : tunables 0 0 0 : slabdata 23 23 0
>>>> kmalloc-8 76563 82432 8 512 1 : tunables 0 0 0 : slabdata 161 161 0
>>>> Really, some waste on these small objects is pure noise on SMP hosts.
>>> In this example, it appears that if all kmalloc-8's were pushed into 32-byte slabs,
>>> we'd lose about 1.8 meg due to pure slab overhead. This would not be noise
>>> on my system.
>> I said :
>> 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
>> I think your 10M cameras are very tiny hosts.
> I agree. Actually, I'm currently doing research for
> items with smaller memory footprints that this. My current
> target is devices with 4M RAM and 8M NOR flash.
> Undoubtedly this is different than what a lot of other
> people are doing with Linux.
>> Using SLUB on them might not be the best choice.
> Indeed. :-)
I think the above assertion still needs some updated measurement.
Is SLUB really a bad choice? Is SLAB the best choice? Or is this a
SLOB use case?
I've been trying to answer this questions, again focusing on
memory-constrained tiny hosts.
If anyone has some insight, it would very much like to hear it.
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