[PATCH v9 15/17] mm: Generalize shrink_slab() calls in shrink_node()

[Kirill Tkhai <ktkhai@virtuozzo.com>]

From: Vladimir Davydov <vdavydov.dev@gmail.com>

The patch makes shrink_slab() be called for root_mem_cgroup
in the same way as it's called for the rest of cgroups.
This simplifies the logic and improves the readability.

Signed-off-by: Vladimir Davydov <vdavydov.dev@gmail.com>
ktkhai: Description written.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Tested-by: Shakeel Butt <shakeelb@google.com>
---
 mm/vmscan.c |   21 ++++++---------------
 1 file changed, 6 insertions(+), 15 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index d7a5b8566869..2aa3cb760189 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -627,10 +627,8 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
  * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
  * unaware shrinkers will receive a node id of 0 instead.
  *
- * @memcg specifies the memory cgroup to target. If it is not NULL,
- * only shrinkers with SHRINKER_MEMCG_AWARE set will be called to scan
- * objects from the memory cgroup specified. Otherwise, only unaware
- * shrinkers are called.
+ * @memcg specifies the memory cgroup to target. Unaware shrinkers
+ * are called only if it is the root cgroup.
  *
  * @priority is sc->priority, we take the number of objects and >> by priority
  * in order to get the scan target.
@@ -644,7 +642,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
 	struct shrinker *shrinker;
 	unsigned long freed = 0;
 
-	if (memcg && !mem_cgroup_is_root(memcg))
+	if (!mem_cgroup_is_root(memcg))
 		return shrink_slab_memcg(gfp_mask, nid, memcg, priority);
 
 	if (!down_read_trylock(&shrinker_rwsem))
@@ -657,9 +655,6 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
 			.memcg = memcg,
 		};
 
-		if (!!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE))
-			continue;
-
 		if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
 			sc.nid = 0;
 
@@ -689,6 +684,7 @@ void drop_slab_node(int nid)
 		struct mem_cgroup *memcg = NULL;
 
 		freed = 0;
+		memcg = mem_cgroup_iter(NULL, NULL, NULL);
 		do {
 			freed += shrink_slab(GFP_KERNEL, nid, memcg, 0);
 		} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
@@ -2708,9 +2704,8 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
 			shrink_node_memcg(pgdat, memcg, sc, &lru_pages);
 			node_lru_pages += lru_pages;
 
-			if (memcg)
-				shrink_slab(sc->gfp_mask, pgdat->node_id,
-					    memcg, sc->priority);
+			shrink_slab(sc->gfp_mask, pgdat->node_id,
+				    memcg, sc->priority);
 
 			/* Record the group's reclaim efficiency */
 			vmpressure(sc->gfp_mask, memcg, false,
@@ -2734,10 +2729,6 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
 			}
 		} while ((memcg = mem_cgroup_iter(root, memcg, &reclaim)));
 
-		if (global_reclaim(sc))
-			shrink_slab(sc->gfp_mask, pgdat->node_id, NULL,
-				    sc->priority);
-
 		if (reclaim_state) {
 			sc->nr_reclaimed += reclaim_state->reclaimed_slab;
 			reclaim_state->reclaimed_slab = 0;