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    SubjectRe: [RFC] [PATCH -mm 0/2] memcg: per cgroup dirty_ratio
    KOSAKI Motohiro wrote:
    >> Currently the problem we are hitting is that we cannot specify pdflush
    >> to have background limits less than 1% of memory. I am currently
    >> finishing up a patch right now that adds a dirty_ratio_millis
    >> interface. I hope to submit the patch to LKML by the end of the week.
    >>
    >> The idea is that we don't want to break backwards compatibility and we
    >> also don't want to have two conflicting knobs in the sysctl or
    >> /proc/sys/vm/ space. I thought adding a new knob for those who want to
    >> specify finer grained functionality was a compromise. So the patch has
    >> a vm_dirty_ratio and a vm_dirty_ratio_millis interface. The first to
    >> specify 0-100% and the second to specify .0 to .999%.
    >>
    >> So to represent 0.125% of RAM we set
    >> vm_dirty_ratio = 0
    >> vm_dirty_ratio_millis = 125
    >>
    >> The same for the background_ratio.
    >
    > Why vm_dirty_ratio = 0.125 is wrong?
    > it is hardly for parser maker, but it have nicer user experience.
    >
    >> I would also prefer using a bytes interface but I am not sure how to
    >> offer that without either removing the legacy interface of the ratios
    >> or by offering a concurrent interface that might be confusing such as
    >> when users are looking at the old one and not aware of a new one.
    >>
    >> Any feedback?
    >
    > Sure.
    > We don't have any motivation of its interface change.

    The more I think about this and the more I would prefer to have an
    interface in KB (or pages) that automatically adjusts the old int percentage
    in dirty_ratio (the same for dirty_background_ratio).

    The parser issue for writing decimal values doesn't seem to be a big
    problem, but if the user expects to read an int from vm_dirty_ratio and
    instead receives something like 0.125, well... this could break
    something. So, IMHO also in this way we're changing the kernel-userspace
    interface.

    -Andrea


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