From: Vladimir Davydov Date: Thu, 12 Feb 2015 22:59:01 +0000 (-0800) Subject: memcg: add rwsem to synchronize against memcg_caches arrays relocation X-Git-Tag: omap-for-v4.1/prcm-dts-mfd-syscon-fix~99^2~89 X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=05257a1a3dcc196c197714b5c9a8dd35b7f6aefc;p=pandora-kernel.git memcg: add rwsem to synchronize against memcg_caches arrays relocation We need a stable value of memcg_nr_cache_ids in kmem_cache_create() (memcg_alloc_cache_params() wants it for root caches), where we only hold the slab_mutex and no memcg-related locks. As a result, we have to update memcg_nr_cache_ids under the slab_mutex, which we can only take on the slab's side (see memcg_update_array_size). This looks awkward and will become even worse when per-memcg list_lru is introduced, which also wants stable access to memcg_nr_cache_ids. To get rid of this dependency between the memcg_nr_cache_ids and the slab_mutex, this patch introduces a special rwsem. The rwsem is held for writing during memcg_caches arrays relocation and memcg_nr_cache_ids updates. Therefore one can take it for reading to get a stable access to memcg_caches arrays and/or memcg_nr_cache_ids. Currently the semaphore is taken for reading only from kmem_cache_create, right before taking the slab_mutex, so right now there's no much point in using rwsem instead of mutex. However, once list_lru is made per-memcg it will allow list_lru initializations to proceed concurrently. Signed-off-by: Vladimir Davydov Cc: Dave Chinner Cc: Johannes Weiner Cc: Michal Hocko Cc: Greg Thelen Cc: Glauber Costa Cc: Alexander Viro Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Cc: Tejun Heo Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-diff-tree failed