• Roman Gushchin's avatar
    mm: memcg/slab: reparent memcg kmem_caches on cgroup removal · fb2f2b0a
    Roman Gushchin authored
    Let's reparent non-root kmem_caches on memcg offlining.  This allows us to
    release the memory cgroup without waiting for the last outstanding kernel
    object (e.g.  dentry used by another application).
    
    Since the parent cgroup is already charged, everything we need to do is to
    splice the list of kmem_caches to the parent's kmem_caches list, swap the
    memcg pointer, drop the css refcounter for each kmem_cache and adjust the
    parent's css refcounter.
    
    Please, note that kmem_cache->memcg_params.memcg isn't a stable pointer
    anymore.  It's safe to read it under rcu_read_lock(), cgroup_mutex held,
    or any other way that protects the memory cgroup from being released.
    
    We can race with the slab allocation and deallocation paths.  It's not a
    big problem: parent's charge and slab global stats are always correct, and
    we don't care anymore about the child usage and global stats.  The child
    cgroup is already offline, so we don't use or show it anywhere.
    
    Local slab stats (NR_SLAB_RECLAIMABLE and NR_SLAB_UNRECLAIMABLE) aren't
    used anywhere except count_shadow_nodes().  But even there it won't break
    anything: after reparenting "nodes" will be 0 on child level (because
    we're already reparenting shrinker lists), and on parent level page stats
    always were 0, and this patch won't change anything.
    
    [guro@fb.com: properly handle kmem_caches reparented to root_mem_cgroup]
      Link: http://lkml.kernel.org/r/20190620213427.1691847-1-guro@fb.com
    Link: http://lkml.kernel.org/r/20190611231813.3148843-11-guro@fb.comSigned-off-by: default avatarRoman Gushchin <guro@fb.com>
    Acked-by: default avatarVladimir Davydov <vdavydov.dev@gmail.com>
    Reviewed-by: default avatarShakeel Butt <shakeelb@google.com>
    Acked-by: default avatarDavid Rientjes <rientjes@google.com>
    Cc: Christoph Lameter <cl@linux.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Michal Hocko <mhocko@suse.com>
    Cc: Waiman Long <longman@redhat.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
    Cc: Pekka Enberg <penberg@kernel.org>
    Cc: Andrei Vagin <avagin@gmail.com>
    Cc: Qian Cai <cai@lca.pw>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    fb2f2b0a
memcontrol.c 175 KB