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    SubjectRe: [RFC] writeback and cgroup
    Hey, Vivek.

    On Wed, Apr 04, 2012 at 04:18:16PM -0400, Vivek Goyal wrote:
    > Hey how about reconsidering my other proposal for which I had posted
    > the patches. And that is keep throttling still at device level. Reads
    > and direct IO get throttled asynchronously but buffered writes get
    > throttled synchronously.
    > Advantages of this scheme.
    > - There are no separate knobs.
    > - All the IO (read, direct IO and buffered write) is controlled using
    > same set of knobs and goes in queue of same cgroup.
    > - Writeback logic has no knowledge of throttling. It just invokes a
    > hook into throttling logic of device queue.
    > I guess this is a hybrid of active writeback throttling and back pressure
    > mechanism.
    > But it still does not solve the NFS issue as well as for direct IO,
    > filesystems still can get serialized, so metadata issue still needs to
    > be resolved. So one can argue that why not go for full "back pressure"
    > method, despite it being more complex.
    > Here is the link, just to refresh the memory. Something to keep in mind
    > while assessing alternatives.

    Hmmm... so, this only works for blk-throttle and not with the weight.
    How do you manage interaction between buffered writes and direct
    writes for the same cgroup?



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