• Vladimir Davydov's avatar
    memcg: add rwsem to synchronize against memcg_caches arrays relocation · 05257a1a
    Vladimir Davydov authored
    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: default avatarVladimir Davydov <vdavydov@parallels.com>
    Cc: Dave Chinner <david@fromorbit.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Michal Hocko <mhocko@suse.cz>
    Cc: Greg Thelen <gthelen@google.com>
    Cc: Glauber Costa <glommer@gmail.com>
    Cc: Alexander Viro <viro@zeniv.linux.org.uk>
    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: Tejun Heo <tj@kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    05257a1a
slab_common.c 26 KB