Re: [PATCH 5/9] slab: link memcg kmem_caches on their associated memory cgroup

Vladimir Davydov
2017-01-14T13:33:56Z

On Sat, Jan 14, 2017 at 12:54:45AM -0500, Tejun Heo wrote:
> With kmem cgroup support enabled, kmem_caches can be created and
> destroyed frequently and a great number of near empty kmem_caches can
> accumulate if there are a lot of transient cgroups and the system is
> not under memory pressure. When memory reclaim starts under such
> conditions, it can lead to consecutive deactivation and destruction of
> many kmem_caches, easily hundreds of thousands on moderately large
> systems, exposing scalability issues in the current slab management
> code. This is one of the patches to address the issue.
>
> While a memcg kmem_cache is listed on its root cache's ->children
> list, there is no direct way to iterate all kmem_caches which are
> assocaited with a memory cgroup. The only way to iterate them is
> walking all caches while filtering out caches which don't match, which
> would be most of them.
>
> This makes memcg destruction operations O(N^2) where N is the total
> number of slab caches which can be huge. This combined with the
> synchronous RCU operations can tie up a CPU and affect the whole
> machine for many hours when memory reclaim triggers offlining and
> destruction of the stale memcgs.
>
> This patch adds mem_cgroup->kmem_caches list which goes through
> memcg_cache_params->kmem_caches_node of all kmem_caches which are
> associated with the memcg. All memcg specific iterations, including
> stat file access, are updated to use the new list instead.
>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Reported-by: Jay Vana <jsvana@fb.com>
> Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Pekka Enberg <penberg@kernel.org>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>

Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>