On Tue, 29 May 2012, Glauber Costa wrote:

quoted

How do you detect that someone is touching it?

kmem_alloc_cache will create mem_cgroup_get_kmem_cache.
(protected by static_branches, so won't happen if you don't have at least
non-root memcg using it)

* Then it detects which memcg the calling process belongs to,
* if it is the root memcg, go back to the allocation as quickly as we
  can
* otherwise, in the creation process, you will notice that each cache
  has an index. memcg will store pointers to the copies and find them by
  the index.

From this point on, all the code of the caches is reused (except for
accounting the page)

Well kmem_cache_alloc cache is the performance critical hotpath.

If you are already there and doing all of that then would it not be better
to simply count the objects allocated and freed per cgroup? Directly
increment and decrement counters in a cgroup? You do not really need to
duplicate the kmem_cache structure and do not need to modify allocators if
you are willing to take that kind of a performance hit. Put a wrapper
around kmem_cache_alloc/free and count things.