linux-kernel - Re: [PATCH 00/16] The new slab memory controller

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Date:   Mon, 13 Jan 2020 14:17:10 +0530
From:   Bharata B Rao <bharata@...ux.ibm.com>
To:     Roman Gushchin <guro@...com>
Cc:     "mhocko@...nel.org" <mhocko@...nel.org>,
        "hannes@...xchg.org" <hannes@...xchg.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        "shakeelb@...gle.com" <shakeelb@...gle.com>,
        "vdavydov.dev@...il.com" <vdavydov.dev@...il.com>,
        "longman@...hat.com" <longman@...hat.com>
Subject: Re: [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.