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>

1 files changed, 0 insertions, 71 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 5cf7726764cc..916892c2b8e0 100644
--- 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;
@@ -822,42 +802,6 @@ static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
 }
 
 /*
- * 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);
 }