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    SubjectRe: [RFC][PATCH -mm 0/5] cgroup: block device i/o controller (v9)
    Hirokazu Takahashi wrote:
    > Hi,
    >> TODO:
    >> * Try to push down the throttling and implement it directly in the I/O
    >> schedulers, using bio-cgroup (
    >> to keep track of the right cgroup context. This approach could lead to more
    >> memory consumption and increases the number of dirty pages (hard/slow to
    >> reclaim pages) in the system, since dirty-page ratio in memory is not
    >> limited. This could even lead to potential OOM conditions, but these problems
    >> can be resolved directly into the memory cgroup subsystem
    >> * Handle I/O generated by kswapd: at the moment there's no control on the I/O
    >> generated by kswapd; try to use the page_cgroup functionality of the memory
    >> cgroup controller to track this kind of I/O and charge the right cgroup when
    >> pages are swapped in/out
    > FYI, this also can be done with bio-cgroup, which determine the owner cgroup
    > of a given anonymous page.
    > Thanks,
    > Hirokazu Takahashi

    That would be great! FYI here is how I would like to proceed:

    - today I'll post a new version of my cgroup-io-throttle patch rebased
    to 2.6.27-rc5-mm1 (it's well tested and seems to be stable enough).
    To keep the things light and simpler I've implemented custom
    get_cgroup_from_page() / put_cgroup_from_page() in the memory
    controller to retrieve the owner of a page, holding a reference to the
    corresponding memcg, during async writes in submit_bio(); this is not
    probably the best way to proceed, and a more generic framework like
    bio-cgroup sounds better, but it seems to work quite well. The only
    problem I've found is that during swap_writepage() the page is not
    assigned to any page_cgroup (page_get_page_cgroup() returns NULL), and
    so I'm not able to charge the cost of this I/O operation to the right
    cgroup. Does bio-cgroup address or even resolve this issue?
    - begin to implement a new branch of cgroup-io-throttle on top of
    - also start to implement an additional request queue to provide first a
    control at the cgroup level and a dispatcher to pass the request to
    the elevator (as suggested by Vivek)


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