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

[Ryo Tsuruta]

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.

Thanks,
Ryo Tsuruta
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