Re: [PATCH 1/9] io-throttle documentation

[Fernando Luis Vázquez Cao]

Andrea Righi wrote:
> On Fri, Apr 17, 2009 at 09:56:31AM +0800, Li Zefan wrote:
> > KAMEZAWA Hiroyuki wrote:
> > > On Tue, 14 Apr 2009 22:21:12 +0200
> > > Andrea Righi <righi.andrea@xxxxxxxxx> wrote:
> > >
> > > > +Example:
> > > > +* Create an association between an io-throttle group and a bio-cgroup group
> > > > +  with "bio" and "blockio" subsystems mounted in different mount points:
> > > > +  # mount -t cgroup -o bio bio-cgroup /mnt/bio-cgroup/
> > > > +  # cd /mnt/bio-cgroup/
> > > > +  # mkdir bio-grp
> > > > +  # cat bio-grp/bio.id
> > > > +  1
> > > > +  # mount -t cgroup -o blockio blockio /mnt/io-throttle
> > > > +  # cd /mnt/io-throttle
> > > > +  # mkdir foo
> > > > +  # echo 1 > foo/blockio.bio_id
> > > Why do we need multiple cgroups at once to track I/O ?
> > > Seems complicated to me.
> > IIUC, it also disallows other subsystems to be binded with blockio subsys:
> >   # mount -t cgroup -o blockio cpuset xxx /mnt
> >   (failed)
> >
> > and if a task is moved from cg1(id=1) to cg2(id=2) in bio subsys, this task
> > will be moved from CG1(id=1) to CG2(id=2) automatically in blockio subsys.
> >
> > All these are odd, unexpected, complex and bug-prone I think..
>
> Implementing bio-cgroup functionality as pure infrastructure framework
> instead of a cgroup subsystem would remove all this oddity and
> complexity.

Andrea, I agree with you completely. In fact, we have been working on that for
a while and have just proposed doing exactly that on a different mail thread
(you are CC'ed). It would be great if you could comment on that proposal.

Thanks,

Fernando

> For example, the actual functionality that I need for the io-throttle
> controller is just an interface to set and get the cgroup owner of a
> page. I think it should be the same also for other potential users of
> bio-cgroup.
>
> So, what about implementing the bio-cgroup functionality as cgroup "page
> tracking" infrastructure and provide the following interfaces:
>
> /*
>  * Encode the cgrp->css.id in page_group->flags
>  */
> void set_cgroup_page_owner(struct page *page, struct cgroup *cgrp);
>
> /*
>  * Returns the cgroup owner of a page, decoding the cgroup id from
>  * page_cgroup->flags.
>  */
> struct cgroup *get_cgroup_page_owner(struct page *page);
>
> This also wouldn't increase the size of page_cgroup because we can
> encode the cgroup id in the unused bits of page_cgroup->flags, as
> originally suggested by Kame.
>
> And I think it could be used also by dm-ioband, even if it's not a
> cgroup-based subsystem... but I may be wrong. Ryo what's your opinion?
>
> -Andrea

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/