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