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

[Andrea Righi]

On Fri, Apr 17, 2009 at 12:25:40PM +0200, Andrea Righi wrote:
> 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

sorry, I meant css_id(struct cgroup_subsys_state *css) here.

>  */
> 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);

Or better, even more generic:

/*
 * Encode id in page_group->flags.
 */
void set_page_id(struct page *page, unsigned short id);

/*
 * Returns the id of a page, decoding it from page_cgroup->flags.
 */
unsigned short get_page_id(struct page *page);

Then we can use css_id() for cgroups, or any kind of ID for other
potential users (dm-ioband, etc.).

-Andrea

> 
> 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?
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