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    SubjectRe: [PATCH 17/23] kmem controller charge/uncharge infrastructure
    On Tue, 24 Apr 2012, Frederic Weisbecker wrote:

    > > This seems horribly inconsistent with memcg charging of user memory since
    > > it charges to p->mm->owner and you're charging to p. So a thread attached
    > > to a memcg can charge user memory to one memcg while charging slab to
    > > another memcg?
    >
    > Charging to the thread rather than the process seem to me the right behaviour:
    > you can have two threads of a same process attached to different cgroups.
    >
    > Perhaps it is the user memory memcg that needs to be fixed?
    >

    No, because memory is represented by mm_struct, not task_struct, so you
    must charge to p->mm->owner to allow for moving threads amongst memcgs
    later for memory.move_charge_at_immigrate. You shouldn't be able to
    charge two different memcgs for memory represented by a single mm.

    > > > +
    > > > + if (!mem_cgroup_kmem_enabled(memcg))
    > > > + goto out;
    > > > +
    > > > + mem_cgroup_get(memcg);
    > > > + ret = memcg_charge_kmem(memcg, gfp, size) == 0;
    > > > + if (ret)
    > > > + mem_cgroup_put(memcg);
    > > > +out:
    > > > + rcu_read_unlock();
    > > > + return ret;
    > > > +}
    > > > +EXPORT_SYMBOL(__mem_cgroup_charge_kmem);
    > > > +
    > > > +void __mem_cgroup_uncharge_kmem(size_t size)
    > > > +{
    > > > + struct mem_cgroup *memcg;
    > > > +
    > > > + rcu_read_lock();
    > > > + memcg = mem_cgroup_from_task(current);
    > > > +
    > > > + if (!mem_cgroup_kmem_enabled(memcg))
    > > > + goto out;
    > > > +
    > > > + mem_cgroup_put(memcg);
    > > > + memcg_uncharge_kmem(memcg, size);
    > > > +out:
    > > > + rcu_read_unlock();
    > > > +}
    > > > +EXPORT_SYMBOL(__mem_cgroup_uncharge_kmem);


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