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SubjectRe: RFC: I/O bandwidth controller
Hi Fernando,

> This RFC ended up being a bit longer than I had originally intended, but
> hopefully it will serve as the start of a fruitful discussion.

Thanks a lot for posting the RFC.

> *** Goals
> 1. Cgroups-aware I/O scheduling (being able to define arbitrary
> groupings of processes and treat each group as a single scheduling
> entity).
> 2. Being able to perform I/O bandwidth control independently on each
> device.
> 3. I/O bandwidth shaping.
> 4. Scheduler-independent I/O bandwidth control.
> 5. Usable with stacking devices (md, dm and other devices of that
> ilk).
> 6. I/O tracking (handle buffered and asynchronous I/O properly).
> The list of goals above is not exhaustive and it is also likely to
> contain some not-so-nice-to-have features so your feedback would be
> appreciated.

I'd like to add the following item to the goals.

7. Selectable from multiple bandwidth control policy (proportion,
maximum rate limiting, ...) like I/O scheduler.

> *** How to move on
> As discussed before, it probably makes sense to have both a block layer
> I/O controller and a elevator-based one, and they could certainly
> cohabitate. As discussed before, all of them need I/O tracking
> capabilities so I would like to suggest the plan below to get things
> started:
> - Improve the I/O tracking patches (see (6) above) until they are in
> mergeable shape.
> - Fix CFQ and AS to use the new I/O tracking functionality to show its
> benefits. If the performance impact is acceptable this should suffice to
> convince the respective maintainer and get the I/O tracking patches
> merged.
> - Implement a block layer resource controller. dm-ioband is a working
> solution and feature rich but its dependency on the dm infrastructure is
> likely to find opposition (the dm layer does not handle barriers
> properly and the maximum size of I/O requests can be limited in some
> cases). In such a case, we could either try to build a standalone
> resource controller based on dm-ioband (which would probably hook into
> generic_make_request) or try to come up with something new.
> - If the I/O tracking patches make it into the kernel we could move on
> and try to get the Cgroup extensions to CFQ and AS mentioned before (see
> (1), (2), and (3) above for details) merged.
> - Delegate the task of controlling the rate at which a task can
> generate dirty pages to the memory controller.

I agree with your plan.
We keep bio-cgroup improving and porting to the latest kernel.

Ryo Tsuruta

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