From: Michal Hocko <mhocko@kernel.org>
To: Balbir Singh <bsingharora@gmail.com>
Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org,
Tejun Heo <tj@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Vladimir Davydov <vdavydov.dev@gmail.com>
Subject: Re: [mm v2 0/3] Support memory cgroup hotplug
Date: Wed, 23 Nov 2016 09:07:45 +0100 [thread overview]
Message-ID: <20161123080744.GG2864@dhcp22.suse.cz> (raw)
In-Reply-To: <342ebcca-b54c-4bc6-906b-653042caae06@gmail.com>
On Wed 23-11-16 18:50:42, Balbir Singh wrote:
>
>
> On 23/11/16 18:25, Michal Hocko wrote:
> > On Wed 23-11-16 15:36:51, Balbir Singh wrote:
> >> In the absence of hotplug we use extra memory proportional to
> >> (possible_nodes - online_nodes) * number_of_cgroups. PPC64 has a patch
> >> to disable large consumption with large number of cgroups. This patch
> >> adds hotplug support to memory cgroups and reverts the commit that
> >> limited possible nodes to online nodes.
> >
> > Balbir,
> > I have asked this in the previous version but there still seems to be a
> > lack of information of _why_ do we want this, _how_ much do we save on
> > the memory overhead on most systems and _why_ the additional complexity
> > is really worth it. Please make sure to add all this in the cover
> > letter.
> >
>
> The data is in the patch referred to in patch 3. The order of waste was
> 200MB for 400 cgroup directories enough for us to restrict possible_map
> to online_map. These patches allow us to have a larger possible map and
> allow onlining nodes not in the online_map, which is currently a restriction
> on ppc64.
How common is to have possible_map >> online_map? If this is ppc64 then
what is the downside of keeping the current restriction instead?
> A typical system that I use has about 100-150 directories, depending on the
> number of users/docker instances/configuration/virtual machines. These numbers
> will only grow as we pack more of these instances on them.
>
> From a complexity view point, the patches are quite straight forward.
Well, I would like to hear more about that. {get,put}_online_memory
at random places doesn't sound all that straightforward to me.
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2016-11-23 8:07 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-23 4:36 Balbir Singh
2016-11-23 4:36 ` [mm v2 1/3] mm: Add basic infrastructure for memcg hotplug support Balbir Singh
2016-11-23 4:36 ` [mm v2 2/3] mm: Move operations to hotplug callbacks Balbir Singh
2016-11-23 4:36 ` [mm v2 3/3] powerpc/mm: fix node_possible_map limitations Balbir Singh
2016-11-23 7:25 ` [mm v2 0/3] Support memory cgroup hotplug Michal Hocko
2016-11-23 7:50 ` Balbir Singh
2016-11-23 8:07 ` Michal Hocko [this message]
2016-11-23 8:37 ` Balbir Singh
2016-11-23 9:28 ` Michal Hocko
2016-11-23 13:05 ` Balbir Singh
2016-11-23 13:22 ` Michal Hocko
2016-11-28 21:10 ` Tejun Heo
2016-11-29 0:09 ` Balbir Singh
2016-11-29 0:42 ` Tejun Heo
2016-11-29 4:57 ` Balbir Singh
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