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    SubjectRe: [PATCH 08/10] blkcg: implement blk-iocost
    Hello.

    On Wed, Aug 28, 2019 at 03:05:58PM -0700, Tejun Heo <tj@kernel.org> wrote:
    > diff --git a/block/blk-iocost.c b/block/blk-iocost.c
    > [...]
    > +static struct cftype ioc_files[] = {
    > + .name = "weight",
    > [...]
    This adds the generic io.weight attribute. How will this compose with
    the weight from IO schedulers? (AFAIK, only BFQ allows proportional
    control as of now. +CC Paolo.)

    I see this attributes are effectively per-cgroup per-device. Apparently,
    one device should have only one weight across hierarchy. Would it make
    sense to have io.bfq.weight and io.cost.weight with disjunctive devices?

    (Alas, I have no idea how to make the users of io.weight happy, when
    proportionality control mechanism seems orthogonal to the weight.
    (Vector weights?))


    > + .name = "cost.qos",
    > + .flags = CFTYPE_ONLY_ON_ROOT,
    > [...]
    > + .name = "cost.model",
    > + .flags = CFTYPE_ONLY_ON_ROOT,
    I'm concerned that these aren't true cgroup attributes. The root cgroup
    would act as container for global configuration options. Wouldn't these
    values better fit as (configurable) attributes of the respective
    devices?

    Secondly, how is CFTYPE_ONLY_ON_ROOT supposed to be presented in cgroup
    namespaces?

    Thanks,
    Michal
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