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    SubjectRe: [PATCH 17/23] kmem controller charge/uncharge infrastructure
    On 04/24/2012 07:54 PM, David Rientjes wrote:
    > On Tue, 24 Apr 2012, Glauber Costa wrote:
    >>> Yes, for user memory, I see charging to p->mm->owner as allowing that
    >>> process to eventually move and be charged to a different memcg and there's
    >>> no way to do proper accounting if the charge is split amongst different
    >>> memcgs because of thread membership to a set of memcgs. This is
    >>> consistent with charges for shared memory being moved when a thread
    >>> mapping it moves to a new memcg, as well.
    >> But that's the problem.
    >> When we are dealing with kernel memory, we are allocating a whole slab page.
    >> It is essentially impossible to track, given a page, which task allocated
    >> which object.
    > Right, so you have to make the distinction that slab charges cannot be
    > migrated by memory.move_charge_at_immigrate (and it's not even specified
    > to do anything beyond user pages in Documentation/cgroups/memory.txt),

    Never intended to.

    > but
    > it would be consistent to charge the same memcg for a process's slab
    > allocations as the process's user allocations.
    > My response was why we shouldn't be charging user pages to
    > mem_cgroup_from_task(current) rather than
    > mem_cgroup_from_task(current->mm->owner) which is what is currently
    > implemented.

    Ah, all right. Well, for user memory I agree with you. My point was
    exactly that user memory can always be pinpointed to a specific address
    space, while kernel memory can't.

    > If that can't be changed so that we can still migrate user memory amongst
    > memcgs for memory.move_charge_at_immigrate, then it seems consistent to
    > have all allocations done by a task to be charged to the same memcg.
    > Hence, I suggested current->mm->owner for slab charging as well.

    All right. This can be done. Although I don't see this as a must for
    slab as already explained, I certainly don't oppose doing so as well.

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