Re: [Q] Default SLAB allocator
Date: Wed Oct 17 2012 - 15:20:44 EST
On Wed, Oct 17, 2012 at 12:13 PM, Eric Dumazet <eric.dumazet@xxxxxxxxx> 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 ?)
>> > # 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.
> Using SLUB on them might not be the best choice.
> First time I ran linux, years ago, it was on 486SX machines with 8M of
> memory (or maybe less, I dont remember exactly). But I no longer use
> this class of machines with recent kernels.
> # size vmlinux
> text data bss dec hex filename
> 10290631 1278976 1896448 13466055 cd79c7 vmlinux
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Potentially stupid question
But is SLAB the one where all objects per cache have a fixed size and
thus you don't have any bookkeeping overhead for the actual
I remember something about one of the allocation mechanisms being
designed for caches of fixed sized objects to minimize the need for
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