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SubjectRe: [PATCH 00/16] The new slab memory controller
On Tue, Dec 10, 2019 at 06:05:20PM +0000, Roman Gushchin wrote:
> >
> > With slab patches
> > # docker stats --no-stream
> > CONTAINER ID NAME CPU % MEM USAGE / LIMIT MEM % NET I/O BLOCK I/O PIDS
> > 24bc99d94d91 sleek 0.00% 1MiB / 25MiB 4.00% 1.81kB / 0B 0B / 0B 0
> >
> > Without slab patches
> > # docker stats --no-stream
> > CONTAINER ID NAME CPU % MEM USAGE / LIMIT MEM % NET I/O BLOCK I/O PIDS
> > 52382f8aaa13 sleek 0.00% 8.688MiB / 25MiB 34.75% 1.53kB / 0B 0B / 0B 0
> >
> > So that's an improvement of MEM USAGE from 8.688MiB to 1MiB. Note that this
> > docker container isn't doing anything useful and hence the numbers
> > aren't representative of any workload.
>
> Cool, that's great!
>
> Small containers is where the relative win is the biggest. Of course, it will
> decrease with the size of containers, but it's expected.
>
> If you'll get any additional numbers, please, share them. It's really
> interesting, especially if you have larger-than-4k pages.

I run a couple of workloads contained within a memory cgroup and measured
memory.kmem.usage_in_bytes and memory.usage_in_bytes with and without
this patchset on PowerPC host. I see significant reduction in
memory.kmem.usage_in_bytes and some reduction in memory.usage_in_bytes.
Before posting the numbers, would like to get the following clarified:

In the original case, the memory cgroup is charged (including kmem charging)
when a new slab page is allocated. In your patch, the subpage charging is
done in slab_pre_alloc_hook routine. However in this case, I couldn't find
where exactly kmem counters are being charged/updated. Hence wanted to
make sure that the reduction in memory.kmem.usage_in_bytes that I am
seeing is indeed real and not because kmem accounting was missed out for
slab usage?

Also, I see all non-root allocations are coming from a single set of
kmem_caches. Guess <kmemcache_name>-memcg caches don't yet show up in
/proc/slabinfo and nor their stats is accumulated into /proc/slabinfo?

Regards,
Bharata.

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