On Sat, Jan 14, 2017 at 12:54:46AM -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. > > slab_caches currently lists all caches including root and memcg ones. > This is the only data structure which lists the root caches and > iterating root caches can only be done by walking the list while > skipping over memcg caches. As there can be a huge number of memcg > caches, this can become very expensive. > > This also can make /proc/slabinfo behave very badly. seq_file > processes reads in 4k chunks and seeks to the previous Nth position on > slab_caches list to resume after each chunk. With a lot of memcg > cache churns on the list, reading /proc/slabinfo can become very slow > and its content often ends up with duplicate and/or missing entries. > > As the previous patch made it unnecessary to walk slab_caches to > iterate memcg-specific caches, there is no reason to keep memcg caches > on the list. This patch makes slab_caches include only the root > caches. As this makes slab_cache->list unused for memcg caches, > ->memcg_params.children_node is removed and ->list is used instead. > > Signed-off-by: Tejun Heo <t...@kernel.org> > Reported-by: Jay Vana <jsv...@fb.com> > Cc: Vladimir Davydov <vdavydov....@gmail.com> > Cc: Christoph Lameter <c...@linux.com> > Cc: Pekka Enberg <penb...@kernel.org> > Cc: David Rientjes <rient...@google.com> > Cc: Joonsoo Kim <iamjoonsoo....@lge.com> > Cc: Andrew Morton <a...@linux-foundation.org> > --- > include/linux/slab.h | 3 --- > mm/slab.h | 3 +-- > mm/slab_common.c | 58 > +++++++++++++++++++++++++--------------------------- > 3 files changed, 29 insertions(+), 35 deletions(-)
IIRC the slab_caches list is also used on cpu/mem online/offline, so you have to patch those places to ensure that memcg caches get updated too. Other than that the patch looks good to me.
