On 06/26/2012 03:10 PM, Michal Hocko wrote:

On Tue 26-06-12 14:31:51, Glauber Costa wrote:

quoted

On 06/26/2012 11:56 AM, Michal Hocko wrote:

quoted

[Adding Ying to CC - they are using hierarchies AFAIU in their workloads]

On Mon 25-06-12 13:49:08, Tejun Heo wrote:
[...]

quoted

A bit of delta but is there any chance we can either deprecate
.use_hierarhcy or at least make it global toggle instead of subtree
thing?

So what you are proposing is to have all subtrees of the root either
hierarchical or not, right?

quoted

This seems needlessly complicated. :(

Toggle wouldn't help much I am afraid. We would still have to
distinguish (non)hierarchical cases. And I am not sure we can make
everything hierarchical easily.
Most users (from my experience) ignored use_hierarchy for some reasons
and the end results might be really unexpected for them if they used
deeper subtrees (which might be needed due to combination with other
controller(s)).

Do we have any idea about who those users are, and how is their
setup commonly done?

Well, most of them use memory controller with combination of other
controller - usually cpuset or cpu - and memcg is used to cap the amount
of memory for each respective group. As I said most of those users
were not aware of use_hierarchy at all.

quoted

We can propose work arounds here, but not without first knowing work
arounds to what =p

No, please no workarounds. It will be even bigger mess.
Maybe a global switch is the first step in the right direction (on by
default). If somebody encounters any issue we can say it can be turned
off (something like one time switch) or advise on how to fix their
layout to fit hierarchy better. We can put WARN_ON_ONCE when the knob is
set to 0 in the second stage and finally remove the whole knob.

Sorry for the wording. I didn't mean work around in the sense of a 
kludge. I meant it as actually proposing solutions to the problem that 
would disrupt people as little as we can.

Well, instead of a global switch, a much easier thing would be to set it 
to 1 by default. It would actually work as a global switch, because we 
always inherit the parent's value.

You can set the root to 0 before you add other groups, but that 
generates a warning, as you suggested.

But after it was first set to 0, he would be free to keep using mixed 
configurations if needed - this way we're likely to find out if there 
are actually users of that around.