[PATCH v3 2/3] mm, shrinker: make memcg low reclaim visible to lru walker isolation function

[Yafang Shao <laoar.shao@xxxxxxxxx>]

A new member memcg_low_reclaim is introduced in shrink_control struct,
which is derived from scan_control struct, in order to tell the shrinker
whether the reclaim session is under memcg low reclaim or not.
The followup patch will use this new member.

Cc: Dave Chinner <dchinner@xxxxxxxxxx>
Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
---
 include/linux/shrinker.h |  3 +++
 mm/vmscan.c              | 27 ++++++++++++++++-----------
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 0f80123..dc42ae5 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -31,6 +31,9 @@ struct shrink_control {
 
 	/* current memcg being shrunk (for memcg aware shrinkers) */
 	struct mem_cgroup *memcg;
+
+	/* derived from struct scan_control */
+	bool memcg_low_reclaim;
 };
 
 #define SHRINK_STOP (~0UL)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5a6445e..c97d005 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -639,10 +639,9 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 
 /**
  * shrink_slab - shrink slab caches
- * @gfp_mask: allocation context
- * @nid: node whose slab caches to target
  * @memcg: memory cgroup whose slab caches to target
- * @priority: the reclaim priority
+ * @sc: scan_control struct for this reclaim session
+ * @nid: node whose slab caches to target
  *
  * Call the shrink functions to age shrinkable caches.
  *
@@ -652,15 +651,18 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
  * @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.
+ * @sc is the scan_control struct, we take the number of objects
+ * and >> by sc->priority in order to get the scan target.
  *
  * Returns the number of reclaimed slab objects.
  */
-static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
-				 struct mem_cgroup *memcg,
-				 int priority)
+static unsigned long shrink_slab(struct mem_cgroup *memcg,
+				 struct scan_control *sc,
+				 int nid)
 {
+	bool memcg_low_reclaim = sc->memcg_low_reclaim;
+	gfp_t gfp_mask = sc->gfp_mask;
+	int priority = sc->priority;
 	unsigned long ret, freed = 0;
 	struct shrinker *shrinker;
 
@@ -682,6 +684,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
 			.gfp_mask = gfp_mask,
 			.nid = nid,
 			.memcg = memcg,
+			.memcg_low_reclaim = memcg_low_reclaim,
 		};
 
 		ret = do_shrink_slab(&sc, shrinker, priority);
@@ -708,6 +711,9 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
 void drop_slab_node(int nid)
 {
 	unsigned long freed;
+	struct scan_control sc = {
+		.gfp_mask = GFP_KERNEL,
+	};
 
 	do {
 		struct mem_cgroup *memcg = NULL;
@@ -715,7 +721,7 @@ void drop_slab_node(int nid)
 		freed = 0;
 		memcg = mem_cgroup_iter(NULL, NULL, NULL);
 		do {
-			freed += shrink_slab(GFP_KERNEL, nid, memcg, 0);
+			freed += shrink_slab(memcg, &sc, nid);
 		} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
 	} while (freed > 10);
 }
@@ -2684,8 +2690,7 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
 
 		shrink_lruvec(lruvec, sc);
 
-		shrink_slab(sc->gfp_mask, pgdat->node_id, memcg,
-			    sc->priority);
+		shrink_slab(memcg, sc, pgdat->node_id);
 
 		/* Record the group's reclaim efficiency */
 		vmpressure(sc->gfp_mask, memcg, false,
-- 
1.8.3.1