mm: memcontrol: remove hierarchy restrictions for swappiness and oom_control

Per-memcg swappiness and oom killing can currently not be tweaked on a
memcg that is part of a hierarchy, but not the root of that hierarchy.
Users have complained that they can't configure this when they turned on
hierarchy mode.  In fact, with hierarchy mode becoming the default, this
restriction disables the tunables entirely.

But there is no good reason for this restriction.  The settings for
swappiness and OOM killing are taken from whatever memcg whose limit
triggered reclaim and OOM invocation, regardless of its position in the
hierarchy tree.

Allow setting swappiness on any group.  The knob on the root memcg already
reads the global VM swappiness, make it writable as well.

Allow disabling the OOM killer on any non-root memcg.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e3a9d7e28091020437957c5f6455e857a7a209a6..fe61b731a5962c92ac5e1ae5e9b8f1d381193418 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5443,22 +5443,14 @@ static int mem_cgroup_swappiness_write(struct cgroup_subsys_state *css,
                                       struct cftype *cft, u64 val)
 {
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
-       struct mem_cgroup *parent = mem_cgroup_from_css(css_parent(&memcg->css));
 
-       if (val > 100 || !parent)
+       if (val > 100)
                return -EINVAL;
 
-       mutex_lock(&memcg_create_mutex);
-
-       /* If under hierarchy, only empty-root can set this value */
-       if ((parent->use_hierarchy) || memcg_has_children(memcg)) {
-               mutex_unlock(&memcg_create_mutex);
-               return -EINVAL;
-       }
-
-       memcg->swappiness = val;
-
-       mutex_unlock(&memcg_create_mutex);
+       if (css_parent(css))
+               memcg->swappiness = val;
+       else
+               vm_swappiness = val;
 
        return 0;
 }
@@ -5790,22 +5782,15 @@ static int mem_cgroup_oom_control_write(struct cgroup_subsys_state *css,
        struct cftype *cft, u64 val)
 {
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
-       struct mem_cgroup *parent = mem_cgroup_from_css(css_parent(&memcg->css));
 
        /* cannot set to root cgroup and only 0 and 1 are allowed */
-       if (!parent || !((val == 0) || (val == 1)))
+       if (!css_parent(css) || !((val == 0) || (val == 1)))
                return -EINVAL;
 
-       mutex_lock(&memcg_create_mutex);
-       /* oom-kill-disable is a flag for subhierarchy. */
-       if ((parent->use_hierarchy) || memcg_has_children(memcg)) {
-               mutex_unlock(&memcg_create_mutex);
-               return -EINVAL;
-       }
        memcg->oom_kill_disable = val;
        if (!val)
                memcg_oom_recover(memcg);
-       mutex_unlock(&memcg_create_mutex);
+
        return 0;
 }