Letting shrink_slab() handle the root_mem_cgroup, and implicitely the
!CONFIG_MEMCG case, allows shrink_zone() to invoke the shrinkers
unconditionally from within the memcg iteration loop.

Signed-off-by: Johannes Weiner <han...@cmpxchg.org>
Acked-by: Michal Hocko <mho...@suse.com>
---
 include/linux/memcontrol.h |  2 ++
 mm/vmscan.c                | 31 ++++++++++++++++---------------
 2 files changed, 18 insertions(+), 15 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 19ff87b..8929685 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -502,6 +502,8 @@ void mem_cgroup_split_huge_fixup(struct page *head);
 #else /* CONFIG_MEMCG */
 struct mem_cgroup;
 
+#define root_mem_cgroup NULL
+
 static inline void mem_cgroup_events(struct mem_cgroup *memcg,
                                     enum mem_cgroup_events_index idx,
                                     unsigned int nr)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 9b52ecf..ecc2125 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -411,6 +411,10 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
        struct shrinker *shrinker;
        unsigned long freed = 0;
 
+       /* Global shrinker mode */
+       if (memcg == root_mem_cgroup)
+               memcg = NULL;
+
        if (memcg && !memcg_kmem_is_active(memcg))
                return 0;
 
@@ -2417,11 +2421,22 @@ static bool shrink_zone(struct zone *zone, struct 
scan_control *sc,
                        shrink_lruvec(lruvec, swappiness, sc, &lru_pages);
                        zone_lru_pages += lru_pages;
 
-                       if (memcg && is_classzone)
+                       /*
+                        * Shrink the slab caches in the same proportion that
+                        * the eligible LRU pages were scanned.
+                        */
+                       if (is_classzone) {
                                shrink_slab(sc->gfp_mask, zone_to_nid(zone),
                                            memcg, sc->nr_scanned - scanned,
                                            lru_pages);
 
+                               if (reclaim_state) {
+                                       sc->nr_reclaimed +=
+                                               reclaim_state->reclaimed_slab;
+                                       reclaim_state->reclaimed_slab = 0;
+                               }
+                       }
+
                        /*
                         * Direct reclaim and kswapd have to scan all memory
                         * cgroups to fulfill the overall scan target for the
@@ -2439,20 +2454,6 @@ static bool shrink_zone(struct zone *zone, struct 
scan_control *sc,
                        }
                } while ((memcg = mem_cgroup_iter(root, memcg, &reclaim)));
 
-               /*
-                * Shrink the slab caches in the same proportion that
-                * the eligible LRU pages were scanned.
-                */
-               if (global_reclaim(sc) && is_classzone)
-                       shrink_slab(sc->gfp_mask, zone_to_nid(zone), NULL,
-                                   sc->nr_scanned - nr_scanned,
-                                   zone_lru_pages);
-
-               if (reclaim_state) {
-                       sc->nr_reclaimed += reclaim_state->reclaimed_slab;
-                       reclaim_state->reclaimed_slab = 0;
-               }
-
                vmpressure(sc->gfp_mask, sc->target_mem_cgroup,
                           sc->nr_scanned - nr_scanned,
                           sc->nr_reclaimed - nr_reclaimed);
-- 
2.6.2

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