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    SubjectRe: Too many I/O controller patches
    On Tue, 05 Aug 2008 09:20:18 -0700
    Dave Hansen <> wrote:

    > On Tue, 2008-08-05 at 11:28 +0200, Andrea Righi wrote:
    > > > Buffered write I/O is also related with cache system.
    > > > We must consider this problem as I/O control.
    > >
    > > Agree. At least, maybe we should consider if an IO controller could be
    > > a valid solution also for these problems.
    > Isn't this one of the core points that we keep going back and forth
    > over? It seems like people are arguing in circles over this:
    > Do we:
    > 1. control potential memory usage by throttling I/O
    > or
    > 2. Throttle I/O when memory is full
    > I might lean toward (1) if we didn't already have a memory controller.
    > But, we have one, and it works. Also, we *already* do (2) in the
    > kernel, so it would seem to graft well onto existing mechanisms that we
    > have.
    > I/O controllers should not worry about memory.
    I agree here ;)

    >They're going to have a hard enough time getting the I/O part right. :)
    memcg have more problems now ;(

    Only a difficult thing to limit dirty-ratio in memcg is how-to-count dirty
    pages. If I/O controller's hook helps, it's good.

    My small concern is "What happens if we throttole I/O bandwidth too small
    under some memcg." In such cgroup, we may see more OOMs because I/O will
    not finish in time.
    A system admin have to find some way to avoid this.

    But please do I/O control first. Dirty-page control is related but different
    layer's problem, I think.


    > Or, am I over-simplifying this?

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