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    SubjectRe: Too many I/O controller patches
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    Hirokazu Takahashi wrote:
    > Hi, Andrea,
    >
    > I'm working with Ryo on dm-ioband and other stuff.
    >
    >>> On Mon, 2008-08-04 at 20:22 +0200, Andrea Righi wrote:
    >>>> But I'm not yet convinced that limiting the IO writes at the device
    >>>> mapper layer is the best solution. IMHO it would be better to throttle
    >>>> applications' writes when they're dirtying pages in the page cache (the
    >>>> io-throttle way), because when the IO requests arrive to the device
    >>>> mapper it's too late (we would only have a lot of dirty pages that are
    >>>> waiting to be flushed to the limited block devices, and maybe this could
    >>>> lead to OOM conditions). IOW dm-ioband is doing this at the wrong level
    >>>> (at least for my requirements). Ryo, correct me if I'm wrong or if I've
    >>>> not understood the dm-ioband approach.
    >>> The avoid-lots-of-page-dirtying problem sounds like a hard one. But, if
    >>> you look at this in combination with the memory controller, they would
    >>> make a great team.
    >>>
    >>> The memory controller keeps you from dirtying more than your limit of
    >>> pages (and pinning too much memory) even if the dm layer is doing the
    >>> throttling and itself can't throttle the memory usage.
    >> mmh... but in this way we would just move the OOM inside the cgroup,
    >> that is a nice improvement, but the main problem is not resolved...
    >
    > The concept of dm-ioband includes it should be used with cgroup memory
    > controller as well as the bio cgroup. The memory controller is supposed
    > to control memory allocation and dirty-page ratio inside each cgroup.
    >
    > Some guys of cgroup memory controller team just started to implement
    > the latter mechanism. They try to make each cgroup have a threshold
    > to limit the number of dirty pages in the group.

    Interesting, they also post a patch or RFC?

    -Andrea


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