revert "memcg: track children in soft limit excess to improve soft limit"

Revert commit 7d910c054be4 ("memcg: track children in soft limit excess
to improve soft limit")

I merged this prematurely - Michal and Johannes still disagree about the
overall design direction and the future remains unclear.

Cc: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 5cf7726..916892c 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -124,7 +124,6 @@ static const char * const mem_cgroup_lru_names[] = {
  */
 enum mem_cgroup_events_target {
        MEM_CGROUP_TARGET_THRESH,
-       MEM_CGROUP_TARGET_SOFTLIMIT,
        MEM_CGROUP_TARGET_NUMAINFO,
        MEM_CGROUP_NTARGETS,
 };
@@ -303,22 +302,6 @@ struct mem_cgroup {
        atomic_t        numainfo_events;
        atomic_t        numainfo_updating;
 #endif
-       /*
-        * Protects soft_contributed transitions.
-        * See mem_cgroup_update_soft_limit
-        */
-       spinlock_t soft_lock;
-
-       /*
-        * If true then this group has increased parents' children_in_excess
-        * when it got over the soft limit.
-        * When a group falls bellow the soft limit, parents' children_in_excess
-        * is decreased and soft_contributed changed to false.
-        */
-       bool soft_contributed;
-
-       /* Number of children that are in soft limit excess */
-       atomic_t children_in_excess;
 
        struct mem_cgroup_per_node *nodeinfo[0];
        /* WARNING: nodeinfo must be the last member here */
@@ -806,9 +789,6 @@ static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
                case MEM_CGROUP_TARGET_THRESH:
                        next = val + THRESHOLDS_EVENTS_TARGET;
                        break;
-               case MEM_CGROUP_TARGET_SOFTLIMIT:
-                       next = val + SOFTLIMIT_EVENTS_TARGET;
-                       break;
                case MEM_CGROUP_TARGET_NUMAINFO:
                        next = val + NUMAINFO_EVENTS_TARGET;
                        break;
@@ -821,42 +801,6 @@ static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
        return false;
 }
 
-/*
- * Called from rate-limited memcg_check_events when enough
- * MEM_CGROUP_TARGET_SOFTLIMIT events are accumulated and it makes sure
- * that all the parents up the hierarchy will be notified that this group
- * is in excess or that it is not in excess anymore. mmecg->soft_contributed
- * makes the transition a single action whenever the state flips from one to
- * the other.
- */
-static void mem_cgroup_update_soft_limit(struct mem_cgroup *memcg)
-{
-       unsigned long long excess = res_counter_soft_limit_excess(&memcg->res);
-       struct mem_cgroup *parent = memcg;
-       int delta = 0;
-
-       spin_lock(&memcg->soft_lock);
-       if (excess) {
-               if (!memcg->soft_contributed) {
-                       delta = 1;
-                       memcg->soft_contributed = true;
-               }
-       } else {
-               if (memcg->soft_contributed) {
-                       delta = -1;
-                       memcg->soft_contributed = false;
-               }
-       }
-
-       /*
-        * Necessary to update all ancestors when hierarchy is used
-        * because their event counter is not touched.
-        */
-       while (delta && (parent = parent_mem_cgroup(parent)))
-               atomic_add(delta, &parent->children_in_excess);
-       spin_unlock(&memcg->soft_lock);
-}
-
 /*
  * Check events in order.
  *
@@ -867,11 +811,8 @@ static void memcg_check_events(struct mem_cgroup *memcg, struct page *page)
        /* threshold event is triggered in finer grain than soft limit */
        if (unlikely(mem_cgroup_event_ratelimit(memcg,
                                                MEM_CGROUP_TARGET_THRESH))) {
-               bool do_softlimit;
                bool do_numainfo __maybe_unused;
 
-               do_softlimit = mem_cgroup_event_ratelimit(memcg,
-                                               MEM_CGROUP_TARGET_SOFTLIMIT);
 #if MAX_NUMNODES > 1
                do_numainfo = mem_cgroup_event_ratelimit(memcg,
                                                MEM_CGROUP_TARGET_NUMAINFO);
@@ -879,8 +820,6 @@ static void memcg_check_events(struct mem_cgroup *memcg, struct page *page)
                preempt_enable();
 
                mem_cgroup_threshold(memcg);
-               if (unlikely(do_softlimit))
-                       mem_cgroup_update_soft_limit(memcg);
 #if MAX_NUMNODES > 1
                if (unlikely(do_numainfo))
                        atomic_inc(&memcg->numainfo_events);
@@ -1864,9 +1803,6 @@ int mem_cgroup_select_victim_node(struct mem_cgroup *memcg)
  * hierarchy if
  *     a) it is over its soft limit
  *     b) any parent up the hierarchy is over its soft limit
- *
- * If the given group doesn't have any children over the limit then it
- * doesn't make any sense to iterate its subtree.
  */
 enum mem_cgroup_filter_t
 mem_cgroup_soft_reclaim_eligible(struct mem_cgroup *memcg,
@@ -1888,8 +1824,6 @@ mem_cgroup_soft_reclaim_eligible(struct mem_cgroup *memcg,
                        break;
        }
 
-       if (!atomic_read(&memcg->children_in_excess))
-               return SKIP_TREE;
        return SKIP;
 }
 
@@ -6021,7 +5955,6 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
        mutex_init(&memcg->thresholds_lock);
        spin_lock_init(&memcg->move_lock);
        vmpressure_init(&memcg->vmpressure);
-       spin_lock_init(&memcg->soft_lock);
 
        return &memcg->css;
 
@@ -6099,10 +6032,6 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
 
        mem_cgroup_invalidate_reclaim_iterators(memcg);
        mem_cgroup_reparent_charges(memcg);
-       if (memcg->soft_contributed) {
-               while ((memcg = parent_mem_cgroup(memcg)))
-                       atomic_dec(&memcg->children_in_excess);
-       }
        mem_cgroup_destroy_all_caches(memcg);
        vmpressure_cleanup(&memcg->vmpressure);
 }