On Thu, Feb 04, 2016 at 03:17:55PM +0300, Vladimir Davydov wrote: > Slab pages are charged in two steps. First, an appropriate per memcg > cache is selected (see memcg_kmem_get_cache) basing on the current > context, then the new slab page is charged to the memory cgroup which > the selected cache was created for (see memcg_charge_slab -> > __memcg_kmem_charge_memcg). It is OK to bypass kmemcg charge at step 1, > but if step 1 succeeded and we successfully allocated a new slab page, > step 2 must be performed, otherwise we would get a per memcg kmem cache > which contains a slab that does not hold a reference to the memory > cgroup owning the cache. Since per memcg kmem caches are destroyed on > memcg css free, this could result in freeing a cache while there are > still active objects in it. > > However, currently we will bypass slab page charge if the memory cgroup > owning the cache is offline (see __memcg_kmem_charge_memcg). This is > very unlikely to occur in practice, because for this to happen a process > must be migrated to a different cgroup and the old cgroup must be > removed while the process is in kmalloc somewhere between steps 1 and 2 > (e.g. trying to allocate a new page). Nevertheless, it's still better > to eliminate such a possibility. > > Signed-off-by: Vladimir Davydov <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
