Re: [Q] Default SLAB allocator
From: Eric Dumazet
Date: Wed Oct 17 2012 - 15:13:31 EST
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 :
<quote>
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
</quote>
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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