[RFC 1/2] mm, vmscan: add priority field to struct shrink_control

[Vlastimil Babka]

Slab reclaim works with reclaim priority, which influences how much to reclaim,
but is not directly passed to individual shrinkers. The next patch introduces a
slab shrinker that uses the priority, so add it to shrink_control and
initialize appropriately. We can then also remove the parameter from
shrink_slab() and trace_mm_shrink_slab_start().

Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
 include/linux/shrinker.h      |  3 +++
 include/trace/events/vmscan.h |  8 +++-----
 mm/vmscan.c                   | 14 ++++++++------
 3 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 0f80123650e2..1066f052be4f 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -29,6 +29,9 @@ struct shrink_control {
 	 */
 	unsigned long nr_scanned;
 
+	/* current reclaim priority */
+	int priority;
+
 	/* current memcg being shrunk (for memcg aware shrinkers) */
 	struct mem_cgroup *memcg;
 };
diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
index 2070df64958e..d42e480977c6 100644
--- a/include/trace/events/vmscan.h
+++ b/include/trace/events/vmscan.h
@@ -185,11 +185,9 @@ DEFINE_EVENT(mm_vmscan_direct_reclaim_end_template, mm_vmscan_memcg_softlimit_re
 TRACE_EVENT(mm_shrink_slab_start,
 	TP_PROTO(struct shrinker *shr, struct shrink_control *sc,
 		long nr_objects_to_shrink, unsigned long cache_items,
-		unsigned long long delta, unsigned long total_scan,
-		int priority),
+		unsigned long long delta, unsigned long total_scan),
 
-	TP_ARGS(shr, sc, nr_objects_to_shrink, cache_items, delta, total_scan,
-		priority),
+	TP_ARGS(shr, sc, nr_objects_to_shrink, cache_items, delta, total_scan),
 
 	TP_STRUCT__entry(
 		__field(struct shrinker *, shr)
@@ -212,7 +210,7 @@ TRACE_EVENT(mm_shrink_slab_start,
 		__entry->cache_items = cache_items;
 		__entry->delta = delta;
 		__entry->total_scan = total_scan;
-		__entry->priority = priority;
+		__entry->priority = sc->priority;
 	),
 
 	TP_printk("%pS %p: nid: %d objects to shrink %ld gfp_flags %s cache items %ld delta %lld total_scan %ld priority %d",
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 469016222cdb..bc5157625cec 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -410,7 +410,7 @@ EXPORT_SYMBOL(unregister_shrinker);
 #define SHRINK_BATCH 128
 
 static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
-				    struct shrinker *shrinker, int priority)
+				    struct shrinker *shrinker)
 {
 	unsigned long freed = 0;
 	unsigned long long delta;
@@ -439,7 +439,7 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 
 	total_scan = nr;
 	if (shrinker->seeks) {
-		delta = freeable >> priority;
+		delta = freeable >> shrinkctl->priority;
 		delta *= 4;
 		do_div(delta, shrinker->seeks);
 	} else {
@@ -484,7 +484,7 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 		total_scan = freeable * 2;
 
 	trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
-				   freeable, delta, total_scan, priority);
+				   freeable, delta, total_scan);
 
 	/*
 	 * Normally, we should not scan less than batch_size objects in one
@@ -562,6 +562,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 		struct shrink_control sc = {
 			.gfp_mask = gfp_mask,
 			.nid = nid,
+			.priority = priority,
 			.memcg = memcg,
 		};
 		struct shrinker *shrinker;
@@ -578,7 +579,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 		    !(shrinker->flags & SHRINKER_NONSLAB))
 			continue;
 
-		ret = do_shrink_slab(&sc, shrinker, priority);
+		ret = do_shrink_slab(&sc, shrinker);
 		if (ret == SHRINK_EMPTY) {
 			clear_bit(i, map->map);
 			/*
@@ -597,7 +598,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 			 *   set_bit()          do_shrink_slab()
 			 */
 			smp_mb__after_atomic();
-			ret = do_shrink_slab(&sc, shrinker, priority);
+			ret = do_shrink_slab(&sc, shrinker);
 			if (ret == SHRINK_EMPTY)
 				ret = 0;
 			else
@@ -666,10 +667,11 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
 		struct shrink_control sc = {
 			.gfp_mask = gfp_mask,
 			.nid = nid,
+			.priority = priority,
 			.memcg = memcg,
 		};
 
-		ret = do_shrink_slab(&sc, shrinker, priority);
+		ret = do_shrink_slab(&sc, shrinker);
 		if (ret == SHRINK_EMPTY)
 			ret = 0;
 		freed += ret;
-- 
2.30.0