On Fri 15-09-17 08:23:01, Roman Gushchin wrote:

On Fri, Sep 15, 2017 at 12:58:26PM +0200, Michal Hocko wrote:

quoted

On Thu 14-09-17 09:05:48, Roman Gushchin wrote:

quoted

On Thu, Sep 14, 2017 at 03:40:14PM +0200, Michal Hocko wrote:

quoted

On Wed 13-09-17 14:56:07, Roman Gushchin wrote:

quoted

On Wed, Sep 13, 2017 at 02:29:14PM +0200, Michal Hocko wrote:

[...]

quoted

quoted

I strongly believe that comparing only leaf memcgs
is more straightforward and it doesn't lead to unexpected results as
mentioned before (kill a small memcg which is a part of the larger
sub-hierarchy).

One of two main goals of this patchset is to introduce cgroup-level
fairness: bigger cgroups should be affected more than smaller,
despite the size of tasks inside. I believe the same principle
should be used for cgroups.

Yes bigger cgroups should be preferred but I fail to see why bigger
hierarchies should be considered as well if they are not kill-all. And
whether non-leaf memcgs should allow kill-all is not entirely clear to
me. What would be the usecase?

We definitely want to support kill-all for non-leaf cgroups.
A workload can consist of several cgroups and we want to clean up
the whole thing on OOM.

Could you be more specific about such a workload? E.g. how can be such a
hierarchy handled consistently when its sub-tree gets killed due to
internal memory pressure?

Or just system-wide OOM.

quoted

Or do you expect that none of the subtree will
have hard limit configured?

And this can also be a case: the whole workload may have hard limit
configured, while internal memcgs have only memory.low set for "soft"
prioritization.

quoted

But then you just enforce a structural restriction on your configuration
because
	root
        /  \
       A    D
      /\   
     B  C

is a different thing than
	root
        / | \
       B  C  D

I actually don't have a strong argument against an approach to select
largest leaf or kill-all-set memcg. I think, in practice there will be
no much difference.

Well, I am worried that the difference will come unexpected when a
deeper hierarchy is needed because of the structural needs.

-- 
Michal Hocko
SUSE Labs