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

[Andrea Righi]

On Mon, Apr 20, 2009 at 06:38:15PM +0900, Ryo Tsuruta wrote:
> Hi Andrea, 
> 
> > Implementing bio-cgroup functionality as pure infrastructure framework
> > instead of a cgroup subsystem would remove all this oddity and
> > complexity.
> > 
> > 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?
> 
> I looked your page_cgroup patch in io-throttle v14, It can also be used
> by dm-ioband. But I'd like to eliminate lock_page_cgroup() to minimize
> overhead. I'll rearrange the bio-cgroup patch according to the functions.

It would be great! Anyway, I don't think it's a trivial task to
completely remove lock_page_cgroup(), especially if we decide to encode
the ID in page_cgroup->flags.

Thanks,
-Andrea
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