linux-kernel - Re: High kmalloc-32 slab cache consumption with 10k containers

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Date:   Wed, 7 Apr 2021 15:57:02 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Bharata B Rao <bharata@...ux.ibm.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        aneesh.kumar@...ux.ibm.com
Subject: Re: High kmalloc-32 slab cache consumption with 10k containers

On Wed 07-04-21 19:13:42, Bharata B Rao wrote:
> On Wed, Apr 07, 2021 at 01:54:48PM +0200, Michal Hocko wrote:
> > On Mon 05-04-21 11:18:48, Bharata B Rao wrote:
> > > Hi,
> > > 
> > > When running 10000 (more-or-less-empty-)containers on a bare-metal Power9
> > > server(160 CPUs, 2 NUMA nodes, 256G memory), it is seen that memory
> > > consumption increases quite a lot (around 172G) when the containers are
> > > running. Most of it comes from slab (149G) and within slab, the majority of
> > > it comes from kmalloc-32 cache (102G)
> > 
> > Is this 10k cgroups a testing enviroment or does anybody really use that
> > in production? I would be really curious to hear how that behaves when
> > those containers are not idle. E.g. global memory reclaim iterating over
> > 10k memcgs will likely be very visible. I do remember playing with
> > similar setups few years back and the overhead was very high.
> 
> This 10k containers is only a test scenario that we are looking at.

OK, this is good to know. I would definitely recommend looking at the
runtime aspect of such a large scale deployment before optimizing for
memory footprint. I do agree that the later is an interesting topic on
its own but I do not expect such a deployment on small machines so the
overhead shouldn't be a showstopper. I would be definitely interested
to hear about the runtime overhead. I do expect some interesting
finidings there.

Btw. I do expect that memory controller will not be the only one
deployed right?

-- 
Michal Hocko
SUSE Labs