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authorRoman Gushchin <guro@fb.com>2019-07-11 20:56:34 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2019-07-12 11:05:44 -0700
commitfb2f2b0adb98bbbbbb51c5a5327f3f90f5dc417e (patch)
tree028755fe0ca55d38534e9b2701caf910f93b8053 /mm/slab_common.c
parent4d96ba3530750fae3f3f01150adfecde96157815 (diff)
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mm: memcg/slab: reparent memcg kmem_caches on cgroup removal
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.com Signed-off-by: Roman Gushchin <guro@fb.com> Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com> Reviewed-by: Shakeel Butt <shakeelb@google.com> Acked-by: David 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: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/slab_common.c')
-rw-r--r--mm/slab_common.c19
1 files changed, 17 insertions, 2 deletions
diff --git a/mm/slab_common.c b/mm/slab_common.c
index ee3971f7fabc..b893eefb6229 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -252,7 +252,8 @@ static void memcg_unlink_cache(struct kmem_cache *s)
} else {
list_del(&s->memcg_params.children_node);
list_del(&s->memcg_params.kmem_caches_node);
- css_put(&s->memcg_params.memcg->css);
+ mem_cgroup_put(s->memcg_params.memcg);
+ WRITE_ONCE(s->memcg_params.memcg, NULL);
}
}
#else
@@ -785,11 +786,13 @@ unlock:
spin_unlock_irq(&memcg_kmem_wq_lock);
}
-void memcg_deactivate_kmem_caches(struct mem_cgroup *memcg)
+void memcg_deactivate_kmem_caches(struct mem_cgroup *memcg,
+ struct mem_cgroup *parent)
{
int idx;
struct memcg_cache_array *arr;
struct kmem_cache *s, *c;
+ unsigned int nr_reparented;
idx = memcg_cache_id(memcg);
@@ -807,6 +810,18 @@ void memcg_deactivate_kmem_caches(struct mem_cgroup *memcg)
kmemcg_cache_deactivate(c);
arr->entries[idx] = NULL;
}
+ nr_reparented = 0;
+ list_for_each_entry(s, &memcg->kmem_caches,
+ memcg_params.kmem_caches_node) {
+ WRITE_ONCE(s->memcg_params.memcg, parent);
+ css_put(&memcg->css);
+ nr_reparented++;
+ }
+ if (nr_reparented) {
+ list_splice_init(&memcg->kmem_caches,
+ &parent->kmem_caches);
+ css_get_many(&parent->css, nr_reparented);
+ }
mutex_unlock(&slab_mutex);
put_online_mems();