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. I've seen machines which end up with hundred thousands of caches and many millions of kernfs_nodes. The current code is O(N^2) on the total number of caches and has synchronous rcu_barrier() and synchronize_sched() in cgroup offline / release path which is executed while holding cgroup_mutex. Combined, this leads to very expensive and slow cache destruction operations which can easily keep running for half a day. This also messes up /proc/slabinfo along with other cache iterating operations. seq_file operates on 4k chunks and on each 4k boundary tries to seek to the last position in the list. With a huge number of caches on the list, this becomes very slow and very prone to the list content changing underneath it leading to a lot of missing and/or duplicate entries. This patchset addresses the scalability problem. * Separate out root and memcg cache lists and add per-memcg list. Update each user to use the appropriate list. * Replace rcu_barrier() and synchronize_rcu() with call_rcu() and call_rcu_sched(). * For dying empty slub caches, remove the sysfs files after deactivation so that we don't end up with millions of sysfs files without any useful information on them. This patchset contains the following nine patches. 0001-Revert-slub-move-synchronize_sched-out-of-slab_mutex.patch 0002-slab-remove-synchronous-rcu_barrier-call-in-memcg-ca.patch 0003-slab-simplify-shutdown_memcg_caches.patch 0004-slab-reorganize-memcg_cache_params.patch 0005-slab-link-memcg-kmem_caches-on-their-associated-memo.patch 0006-slab-don-t-put-memcg-caches-on-slab_caches-list.patch 0007-slab-introduce-__kmemcg_cache_deactivate.patch 0008-slab-remove-synchronous-synchronize_sched-from-memcg.patch 0009-slab-remove-slub-sysfs-interface-files-early-for-emp.patch 0001 reverts an existing optimization to prepare for the following changes. 0002 replaces rcu_barrier() in release path with call_rcu(). 0003-0006 separate out the lists. 0007-0008 replace synchronize_sched() in slub destruction path with call_rcu_sched(). 0009 removes sysfs files early for empty dying caches. This patchset is on top of the current linus#master a121103c9228 and also available in the following git branch. git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git review-kmemcg-scalability diffstat follows. Thanks. include/linux/memcontrol.h | 1 include/linux/slab.h | 39 ++++- include/linux/slab_def.h | 5 include/linux/slub_def.h | 9 - mm/memcontrol.c | 7 - mm/slab.c | 7 + mm/slab.h | 21 ++- mm/slab_common.c | 306 ++++++++++++++++++++++++--------------------- mm/slub.c | 54 +++++++ 9 files changed, 283 insertions(+), 166 deletions(-) -- tejun -- 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>