revert "memcg: enhance memcg iterator to support predicates"

Revert commit de57780dc659 ("memcg: enhance memcg iterator to support
predicates")

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>

2 files changed, 26 insertions, 60 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 916892c2b8e0..65e7bec4b0f0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -862,15 +862,6 @@ struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm)
         return memcg;
 }
 
-static enum mem_cgroup_filter_t
-mem_cgroup_filter(struct mem_cgroup *memcg, struct mem_cgroup *root,
-                mem_cgroup_iter_filter cond)
-{
-        if (!cond)
-                return VISIT;
-        return cond(memcg, root);
-}
-
 /*
  * Returns a next (in a pre-order walk) alive memcg (with elevated css
  * ref. count) or NULL if the whole root's subtree has been visited.
@@ -878,7 +869,7 @@ mem_cgroup_filter(struct mem_cgroup *memcg, struct mem_cgroup *root,
  * helper function to be used by mem_cgroup_iter
  */
 static struct mem_cgroup *__mem_cgroup_iter_next(struct mem_cgroup *root,
-                struct mem_cgroup *last_visited, mem_cgroup_iter_filter cond)
+                struct mem_cgroup *last_visited)
 {
         struct cgroup_subsys_state *prev_css, *next_css;
 
@@ -896,31 +887,11 @@ skip_node:
         if (next_css) {
                 struct mem_cgroup *mem = mem_cgroup_from_css(next_css);
 
-                switch (mem_cgroup_filter(mem, root, cond)) {
-                case SKIP:
+                if (css_tryget(&mem->css))
+                        return mem;
+                else {
                         prev_css = next_css;
                         goto skip_node;
-                case SKIP_TREE:
-                        if (mem == root)
-                                return NULL;
-                        /*
-                         * css_rightmost_descendant is not an optimal way to
-                         * skip through a subtree (especially for imbalanced
-                         * trees leaning to right) but that's what we have right
-                         * now. More effective solution would be traversing
-                         * right-up for first non-NULL without calling
-                         * css_next_descendant_pre afterwards.
-                         */
-                        prev_css = css_rightmost_descendant(next_css);
-                        goto skip_node;
-                case VISIT:
-                        if (css_tryget(&mem->css))
-                                return mem;
-                        else {
-                                prev_css = next_css;
-                                goto skip_node;
-                        }
-                        break;
                 }
         }
 
@@ -984,7 +955,6 @@ static void mem_cgroup_iter_update(struct mem_cgroup_reclaim_iter *iter,
  * @root: hierarchy root
  * @prev: previously returned memcg, NULL on first invocation
  * @reclaim: cookie for shared reclaim walks, NULL for full walks
- * @cond: filter for visited nodes, NULL for no filter
  *
  * Returns references to children of the hierarchy below @root, or
  * @root itself, or %NULL after a full round-trip.
@@ -997,18 +967,15 @@ static void mem_cgroup_iter_update(struct mem_cgroup_reclaim_iter *iter,
  * divide up the memcgs in the hierarchy among all concurrent
  * reclaimers operating on the same zone and priority.
  */
-struct mem_cgroup *mem_cgroup_iter_cond(struct mem_cgroup *root,
+struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
                                    struct mem_cgroup *prev,
-                                   struct mem_cgroup_reclaim_cookie *reclaim,
-                                   mem_cgroup_iter_filter cond)
+                                   struct mem_cgroup_reclaim_cookie *reclaim)
 {
         struct mem_cgroup *memcg = NULL;
         struct mem_cgroup *last_visited = NULL;
 
-        if (mem_cgroup_disabled()) {
-                /* first call must return non-NULL, second return NULL */
-                return (struct mem_cgroup *)(unsigned long)!prev;
-        }
+        if (mem_cgroup_disabled())
+                return NULL;
 
         if (!root)
                 root = root_mem_cgroup;
@@ -1019,9 +986,7 @@ struct mem_cgroup *mem_cgroup_iter_cond(struct mem_cgroup *root,
         if (!root->use_hierarchy && root != root_mem_cgroup) {
                 if (prev)
                         goto out_css_put;
-                if (mem_cgroup_filter(root, root, cond) == VISIT)
-                        return root;
-                return NULL;
+                return root;
         }
 
         rcu_read_lock();
@@ -1044,7 +1009,7 @@ struct mem_cgroup *mem_cgroup_iter_cond(struct mem_cgroup *root,
                         last_visited = mem_cgroup_iter_load(iter, root, &seq);
                 }
 
-                memcg = __mem_cgroup_iter_next(root, last_visited, cond);
+                memcg = __mem_cgroup_iter_next(root, last_visited);
 
                 if (reclaim) {
                         mem_cgroup_iter_update(iter, last_visited, memcg, seq);
@@ -1055,11 +1020,7 @@ struct mem_cgroup *mem_cgroup_iter_cond(struct mem_cgroup *root,
                                 reclaim->generation = iter->generation;
                 }
 
-                /*
-                 * We have finished the whole tree walk or no group has been
-                 * visited because filter told us to skip the root node.
-                 */
-                if (!memcg && (prev || (cond && !last_visited)))
+                if (prev && !memcg)
                         goto out_unlock;
         }
 out_unlock:
@@ -1804,14 +1765,13 @@ int mem_cgroup_select_victim_node(struct mem_cgroup *memcg)
  *      a) it is over its soft limit
  *      b) any parent up the hierarchy is over its soft limit
  */
-enum mem_cgroup_filter_t
-mem_cgroup_soft_reclaim_eligible(struct mem_cgroup *memcg,
+bool mem_cgroup_soft_reclaim_eligible(struct mem_cgroup *memcg,
                 struct mem_cgroup *root)
 {
         struct mem_cgroup *parent = memcg;
 
         if (res_counter_soft_limit_excess(&memcg->res))
-                return VISIT;
+                return true;
 
         /*
          * If any parent up to the root in the hierarchy is over its soft limit
@@ -1819,12 +1779,12 @@ mem_cgroup_soft_reclaim_eligible(struct mem_cgroup *memcg,
          */
         while ((parent = parent_mem_cgroup(parent))) {
                 if (res_counter_soft_limit_excess(&parent->res))
-                        return VISIT;
+                        return true;
                 if (parent == root)
                         break;
         }
 
-        return SKIP;
+        return false;
 }
 
 static DEFINE_SPINLOCK(memcg_oom_lock);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index cdd300b81485..17a7134de4d7 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2185,16 +2185,21 @@ __shrink_zone(struct zone *zone, struct scan_control *sc, bool soft_reclaim)
                         .zone = zone,
                         .priority = sc->priority,
                 };
-                struct mem_cgroup *memcg = NULL;
-                mem_cgroup_iter_filter filter = (soft_reclaim) ?
-                        mem_cgroup_soft_reclaim_eligible : NULL;
+                struct mem_cgroup *memcg;
 
                 nr_reclaimed = sc->nr_reclaimed;
                 nr_scanned = sc->nr_scanned;
 
-                while ((memcg = mem_cgroup_iter_cond(root, memcg, &reclaim, filter))) {
+                memcg = mem_cgroup_iter(root, NULL, &reclaim);
+                do {
                         struct lruvec *lruvec;
 
+                        if (soft_reclaim &&
+                            !mem_cgroup_soft_reclaim_eligible(memcg, root)) {
+                                memcg = mem_cgroup_iter(root, memcg, &reclaim);
+                                continue;
+                        }
+
                         lruvec = mem_cgroup_zone_lruvec(zone, memcg);
 
                         shrink_lruvec(lruvec, sc);
@@ -2214,7 +2219,8 @@ __shrink_zone(struct zone *zone, struct scan_control *sc, bool soft_reclaim)
                                 mem_cgroup_iter_break(root, memcg);
                                 break;
                         }
-                }
+                        memcg = mem_cgroup_iter(root, memcg, &reclaim);
+                } while (memcg);
 
                 vmpressure(sc->gfp_mask, sc->target_mem_cgroup,
                            sc->nr_scanned - nr_scanned,