RFC: Attaching threads to cgroups is OK?

[Hirokazu Takahashi]

Hi Fernando!

> Hi Balbir, Kamezawa-san!
> 
> On Tue, 2008-08-19 at 17:57 +0530, Balbir Singh wrote:
> > >> Tsuruta-san, how about your bio-cgroup's tracking concerning this?
> > >> If we want to use your tracking functions for each threads seperately, 
> > >> there seems to be a problem.
> > >> ===cf. mm_get_bio_cgroup()===================
> > >>            owner
> > >> mm_struct ----> task_struct ----> bio_cgroup
> > >> =============================================
> > >> In my understanding, the mm_struct of a thread is same as its parent's.
> > >> So, even if we attach the TIDs of some threads to different cgroups the 
> > >> tracking always returns the same bio_cgroup -- its parent's group.
> > >> Do you have some policy about in which case we can use your tracking?
> > >>
> > > It's will be resitriction when io-controller reuse information of the owner
> > > of memory. But if it's very clear who issues I/O (by tracking read/write
> > > syscall), we may have chance to record the issuer of I/O to page_cgroup
> > > struct. 
> > 
> > We already do some tracking (at dirty time, IIRC) for task IO accounting. For
> > the memory controller, tasks are virtually grouped by the mm_struct.
> Thank you for your comments and the links.
> 
> When it comes to io-tracking such mm_struct-based grouping might not
> desirable. If everyone agrees, we could try to decouple bio cgroup from
> that memory controller-specific bits.