Re: [PATCH v3 2/7] socket: initial cgroup code.

[Balbir Singh]

On Thu, Sep 22, 2011 at 11:30 AM, Greg Thelen <gthelen@xxxxxxxxxx> wrote:
> On Wed, Sep 21, 2011 at 11:59 AM, Glauber Costa <glommer@xxxxxxxxxxxxx> wrote:
>> Right now I am working under the assumption that tasks are long lived inside
>> the cgroup. Migration potentially introduces some nasty locking problems in
>> the mem_schedule path.
>>
>> Also, unless I am missing something, the memcg already has the policy of
>> not carrying charges around, probably because of this very same complexity.
>>
>> True that at least it won't EBUSY you... But I think this is at least a way
>> to guarantee that the cgroup under our nose won't disappear in the middle of
>> our allocations.
>
> Here's the memcg user page behavior using the same pattern:
>
> 1. user page P is allocate by task T in memcg M1
> 2. T is moved to memcg M2.  The P charge is left behind still charged
> to M1 if memory.move_charge_at_immigrate=0; or the charge is moved to
> M2 if memory.move_charge_at_immigrate=1.
> 3. rmdir M1 will try to reclaim P (if P was left in M1).  If unable to
> reclaim, then P is recharged to parent(M1).
>

We also have some magic in page_referenced() to remove pages
referenced from different containers. What we do is try not to
penalize a cgroup if another cgroup is referencing this page and the
page under consideration is being reclaimed from the cgroup that
touched it.

Balbir Singh
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