SLUB creates a per-cache directory under /sys/kernel/slab which hosts a
bunch of debug files. Usually, there aren't that many caches on a
system and this doesn't really matter; however, if memcg is in use, each
cache can have per-cgroup sub-caches. SLUB creates the same directories
for these sub-caches under /sys/kernel/slab/$CACHE/cgroup.
Unfortunately, because there can be a lot of cgroups, active or
draining, the product of the numbers of caches, cgroups and files in
each directory can reach a very high number - hundreds of thousands is
commonplace. Millions and beyond aren't difficult to reach either.
What's under /sys/kernel/slab is primarily for debugging and the
information and control on the a root cache already cover its
sub-caches. While having a separate directory for each sub-cache can be
helpful for development, it doesn't make much sense to pay this amount
of overhead by default.
This patch introduces a boot parameter slub_memcg_sysfs which determines
whether to create sysfs directories for per-memcg sub-caches. It also
adds CONFIG_SLUB_MEMCG_SYSFS_ON which determines the boot parameter's
default value and defaults to 0.
[akpm@linux-foundation.org: kset_unregister(NULL) is legal]
Link: http://lkml.kernel.org/r/20170204145203.GB26958@mtj.duckdns.org
Signed-off-by: Tejun Heo <tj@kernel.org>
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: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1663f26df3