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SubjectRe: [RFC][PATCH 1/2] memcg: res_counter hierarchy
KAMEZAWA Hiroyuki wrote:
> This patch tries to implements _simple_ 'hierarchy policy' in res_counter.
>
> While several policy of hierarchy can be considered, this patch implements
> simple one
> - the parent includes, over-commits the child
> - there are no shared resource

I am not sure if this is desirable. The concept of a hierarchy applies really
well when there are shared resources.

> - dynamic hierarchy resource usage management in the kernel is not necessary
>

Could you please elaborate as to why? I am not sure I understand your point

> works as following.
>
> 1. create a child. set default child limits to be 0.
> 2. set limit to child.
> 2-a. before setting limit to child, prepare enough room in parent.
> 2-b. increase 'usage' of parent by child's limit.

The problem with this is that you are forcing the parent will run into a reclaim
loop even if the child is not using the assigned limit to it.

> 3. the child sets its limit to the val moved from the parent.
> the parent remembers what amount of resource is to the children.
>

All of this needs to be dynamic

> Above means that
> - a directory's usage implies the sum of all sub directories +
> own usage.
> - there are no shared resource between parent <-> child.
>
> Pros.
> - simple and easy policy.
> - no hierarchy overhead.
> - no resource share among child <-> parent. very suitable for multilevel
> resource isolation.

Sharing is an important aspect of hierachies. I am not convinced of this
approach. Did you look at the patches I sent out? Was there something
fundamentally broken in them?

[snip]

--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL


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