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    SubjectRe: [PATCH v2 04/11] kmem accounting basic infrastructure
    On 08/15/2012 05:26 PM, Michal Hocko wrote:
    > On Wed 15-08-12 17:04:31, Glauber Costa wrote:
    >> On 08/15/2012 05:02 PM, Michal Hocko wrote:
    >>> On Wed 15-08-12 16:53:40, Glauber Costa wrote:
    >>> [...]
    >>>>>>> This doesn't check for the hierachy so kmem_accounted might not be in
    >>>>>>> sync with it's parents. mem_cgroup_create (below) needs to copy
    >>>>>>> kmem_accounted down from the parent and the above needs to check if this
    >>>>>>> is a similar dance like mem_cgroup_oom_control_write.
    >>>>>>>
    >>>>>>
    >>>>>> I don't see why we have to.
    >>>>>>
    >>>>>> I believe in a A/B/C hierarchy, C should be perfectly able to set a
    >>>>>> different limit than its parents. Note that this is not a boolean.
    >>>>>
    >>>>> Ohh, I wasn't clear enough. I am not against setting the _limit_ I just
    >>>>> meant that the kmem_accounted should be consistent within the hierarchy.
    >>>>>
    >>>>
    >>>> If a parent of yours is accounted, you get accounted as well. This is
    >>>> not the state in this patch, but gets added later. Isn't this enough ?
    >>>
    >>> But if the parent is not accounted, you can set the children to be
    >>> accounted, right? Or maybe this is changed later in the series? I didn't
    >>> get to the end yet.
    >>>
    >>
    >> Yes, you can. Do you see any problem with that?
    >
    > Well, if a child contributes with the kmem charges upwards the hierachy
    > then a parent can have kmem.usage > 0 with disabled accounting.
    > I am not saying this is a no-go but it definitely is confusing and I do
    > not see any good reason for it. I've considered it as an overlook rather
    > than a deliberate design decision.
    >

    No, it is not an overlook.
    It is theoretically possible to skip accounting on non-limited parents,
    but how expensive is that? This is, indeed, confusing.

    Of course I can be biased, but the way I see it, once you have
    hierarchy, you account everything your child accounts.

    I really don't see what is the concern here.


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