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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. slub uses synchronize_sched() to deactivate a memcg cache. synchronize_sched() is an expensive and slow operation and doesn't scale when a huge number of caches are destroyed back-to-back. While there used to be a simple batching mechanism, the batching was too restricted to be helpful. This patch implements slab_deactivate_memcg_cache_rcu_sched() which slub can use to schedule sched RCU callback instead of performing synchronize_sched() synchronously while holding cgroup_mutex. While this adds online cpus, mems and slab_mutex operations, operating on these locks back-to-back from the same kworker, which is what's gonna happen when there are many to deactivate, isn't expensive at all and this gets rid of the scalability problem completely. Link: http://lkml.kernel.org/r/20170117235411.9408-9-tj@kernel.org Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Jay Vana <jsvana@fb.com> Acked-by: 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> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.