Re: [PATCH v2 2/5] memcg: provide root figures from system totals

[Michal Hocko <mhocko@suse.cz>]

On Wed 20-03-13 11:03:17, Glauber Costa wrote:
> On 03/19/2013 04:55 PM, Michal Hocko wrote:
> > On Tue 19-03-13 13:46:50, Michal Hocko wrote:
> >> On Tue 05-03-13 17:10:55, Glauber Costa wrote:
> >>> For the root memcg, there is no need to rely on the res_counters if hierarchy
> >>> is enabled The sum of all mem cgroups plus the tasks in root itself, is
> >>> necessarily the amount of memory used for the whole system. Since those figures
> >>> are already kept somewhere anyway, we can just return them here, without too
> >>> much hassle.
> >>>
> >>> Limit and soft limit can't be set for the root cgroup, so they are left at
> >>> RESOURCE_MAX. Failcnt is left at 0, because its actual meaning is how many
> >>> times we failed allocations due to the limit being hit. We will fail
> >>> allocations in the root cgroup, but the limit will never the reason.
> >>
> >> I do not like this very much to be honest. It just adds more hackery...
> >> Why cannot we simply not account if nr_cgroups == 1 and move relevant
> >> global counters to the root at the moment when a first group is
> >> created?
> > 
> > OK, it seems that the very next patch does what I was looking for. So
> > why all the churn in this patch?
> > Why do you want to make root even more special?
> 
> Because I am operating under the assumption that we want to handle that
> transparently and keep things working. If you tell me: "Hey, reading
> memory.usage_in_bytes from root should return 0!", then I can get rid of
> that.

If you simply switch to accounting for root then you do not have to care
about this, don't you?

> The fact that I keep bypassing when hierarchy is present, it is
> more of a reuse of the infrastructure since it's there anyway.
> 
> Also, I would like the root memcg to be usable, albeit cheap, for
> projects like memory pressure notifications.
 
root memcg without any childre, right?

-- 
Michal Hocko
SUSE Labs

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>