Hi, cgroups that use css_id only have this number assigned after ->create() returns. This means it is not possible to use this number for anything during cgroup initialization. There are situations in which it may come handy: in the kmemcg-slab patchset, for instance, each memcg that has a limit on kernel memory will use its css_id as an index in an array of per-memcg kmem_caches. This array increases in size (in bulks, of course) as the maximum possible index grows, so we need to be aware of that early. This could be achieved with a hook called after ->create(). Such a hook exists: this is ->post_clone(). However, this is called only for cgroups that set the clone_children flag. I believe a more general hook is useful, and the following two patches generalize post_clone() into a hook that is always called after create. As I mentioned, I intend to do memory allocations from that hook so it can fail (in patch 2, for simplicity). I consider a general hook acceptable and useful, and is the simplest solution to the problem I face. Let me know what you guys think of it. Glauber Costa (2): generalize post_clone into post_create allow post_create to fail Documentation/cgroups/cgroups.txt | 13 +++++++------ include/linux/cgroup.h | 7 ++++++- kernel/cgroup.c | 12 +++++------- kernel/cpuset.c | 19 +++++++++++-------- 4 files changed, 29 insertions(+), 22 deletions(-) -- 1.7.11.7 -- 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>