On Mon, Aug 13 2012, Glauber Costa wrote: >>> > + WARN_ON(mem_cgroup_is_root(memcg)); >>> > + size = (1 << order) << PAGE_SHIFT; >>> > + memcg_uncharge_kmem(memcg, size); >>> > + mem_cgroup_put(memcg); >> Why do we need ref-counting here ? kmem res_counter cannot work as >> reference ? > This is of course the pair of the mem_cgroup_get() you commented on > earlier. If we need one, we need the other. If we don't need one, we > don't need the other =) > > The guarantee we're trying to give here is that the memcg structure will > stay around while there are dangling charges to kmem, that we decided > not to move (remember: moving it for the stack is simple, for the slab > is very complicated and ill-defined, and I believe it is better to treat > all kmem equally here) By keeping memcg structures hanging around until the last referring kmem page is uncharged do such zombie memcg each consume a css_id and thus put pressure on the 64k css_id space? I imagine in pathological cases this would prevent creation of new cgroups until these zombies are dereferenced. Is there any way to see how much kmem such zombie memcg are consuming? I think we could find these with for_each_mem_cgroup_tree(root_mem_cgroup). Basically, I'm wanting to know where kernel memory has been allocated. For live memcg, an admin can cat memory.kmem.usage_in_bytes. But for zombie memcg, I'm not sure how to get this info. It looks like the root_mem_cgroup memory.kmem.usage_in_bytes is not hierarchically charged. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>