Re: [Q] Default SLAB allocator
From: Tim Bird
Date: Wed Oct 17 2012 - 14:42:12 EST
On 10/16/2012 12:16 PM, Eric Dumazet wrote:
> On Tue, 2012-10-16 at 15:27 -0300, Ezequiel Garcia wrote:
>> Yes, we have some numbers:
>> Are they too informal? I can add some details...
>> They've been measured on a **very** minimal setup, almost every option
>> is stripped out, except from initramfs, sysfs, and trace.
>> On this scenario, strings allocated for file names and directories
>> created by sysfs
>> are quite noticeable, being 4-16 bytes, and produce a lot of fragmentation from
>> that 32 byte cache at SLAB.
>> Is an option to enable small caches on SLUB and SLAB worth it?
> Random small web server :
> # free
> total used free shared buffers cached
> Mem: 7884536 5412572 2471964 0 155440 1803340
> -/+ buffers/cache: 3453792 4430744
> Swap: 2438140 51164 2386976
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... :-)
> # 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.
> (Waste on bigger objects is probably more important by orders of magnitude)
I need to run some measurements on systems that are more similar to what
we're deploying in products. I'll see if I can share them.
Architecture Group Chair, CE Workgroup of the Linux Foundation
Senior Staff Engineer, Sony Network Entertainment
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/