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

    From: Andrea Righi <righi.andrea@gmail.com>
    Subject: Re: [PATCH 1/9] io-throttle documentation
    Date: Mon, 20 Apr 2009 17:00:53 +0200

    > 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've come up with an idea to coexist blkio-cgroup and io-throttle.
    blkio-cgroup provides a function to get a cgroup with the specified ID.

    /* Should be called under rcu_read_lock() */
    struct cgroup *blkio_cgroup_lookup(int id)
    {
    struct cgroup *cgrp;
    struct cgroup_subsys_state *css;

    if (blkio_cgroup_disabled())
    return NULL;

    css = css_lookup(&blkio_cgroup_subsys, id);
    if (!css)
    return NULL;
    cgrp = css->cgroup;
    return cgrp;
    }

    Then io-throttle can get a struct iothrottle which belongs to the
    cgroup by using the above function.

    static struct iothrottle *iothrottle_lookup(int id)
    {
    struct cgroup *grp;
    struct iothrottle *iot;

    ...
    grp = blkio_cgroup_lookup(id);
    if (!grp)
    return NULL
    iot = cgroup_to_iothrottle(grp);
    ...
    }

    What do you think about this way?

    Thanks,
    Ryo Tsuruta


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