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    SubjectRe: [PATCH v2 04/11] kmem accounting basic infrastructure
    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.
    --
    Michal Hocko
    SUSE Labs


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