[PATCH 03/10] mm: shrinker: Add new stats for .to_text()

[Kent Overstreet <kent.overstreet@linux.dev>]

Add a few new shrinker stats.

number of objects requested to free, number of objects freed:

Shrinkers won't necessarily free all objects requested for a variety of
reasons, but if the two counts are wildly different something is likely
amiss.

.scan_objects runtime:

If one shrinker is taking an excessive amount of time to free
objects that will block kswapd from running other shrinkers.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: linux-mm@kvack.org
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
---
 include/linux/shrinker.h |  6 ++++++
 mm/shrinker.c            | 23 ++++++++++++++++++++++-
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 6193612617a1..106622ddac77 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -118,6 +118,12 @@ struct shrinker {
 #endif
 	/* objs pending delete, per node */
 	atomic_long_t *nr_deferred;
+
+	atomic_long_t	objects_requested_to_free;
+	atomic_long_t	objects_freed;
+	unsigned long	last_freed;	/* timestamp, in jiffies */
+	unsigned long	last_scanned;	/* timestamp, in jiffies */
+	atomic64_t	ns_run;
 };
 #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
 
diff --git a/mm/shrinker.c b/mm/shrinker.c
index ad52c269bb48..feaa8122afc9 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -430,13 +430,24 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 	       total_scan >= freeable) {
 		unsigned long ret;
 		unsigned long nr_to_scan = min(batch_size, total_scan);
+		u64 start_time = ktime_get_ns();
+
+		atomic_long_add(nr_to_scan, &shrinker->objects_requested_to_free);
 
 		shrinkctl->nr_to_scan = nr_to_scan;
 		shrinkctl->nr_scanned = nr_to_scan;
 		ret = shrinker->scan_objects(shrinker, shrinkctl);
+
+		atomic64_add(ktime_get_ns() - start_time, &shrinker->ns_run);
 		if (ret == SHRINK_STOP)
 			break;
 		freed += ret;
+		unsigned long now = jiffies;
+		if (ret) {
+			atomic_long_add(ret, &shrinker->objects_freed);
+			shrinker->last_freed = now;
+		}
+		shrinker->last_scanned = now;
 
 		count_vm_events(SLABS_SCANNED, shrinkctl->nr_scanned);
 		total_scan -= shrinkctl->nr_scanned;
@@ -812,9 +823,19 @@ EXPORT_SYMBOL_GPL(shrinker_free);
 void shrinker_to_text(struct seq_buf *out, struct shrinker *shrinker)
 {
 	struct shrink_control sc = { .gfp_mask = GFP_KERNEL, };
+	unsigned long nr_freed = atomic_long_read(&shrinker->objects_freed);
 
 	seq_buf_puts(out, shrinker->name);
-	seq_buf_printf(out, " objects: %lu\n", shrinker->count_objects(shrinker, &sc));
+	seq_buf_putc(out, '\n');
+
+	seq_buf_printf(out, "objects:             %lu\n", shrinker->count_objects(shrinker, &sc));
+	seq_buf_printf(out, "requested to free:   %lu\n", atomic_long_read(&shrinker->objects_requested_to_free));
+	seq_buf_printf(out, "objects freed:       %lu\n", nr_freed);
+	seq_buf_printf(out, "last scanned:        %li sec ago\n", (jiffies - shrinker->last_scanned) / HZ);
+	seq_buf_printf(out, "last freed:          %li sec ago\n", (jiffies - shrinker->last_freed) / HZ);
+	seq_buf_printf(out, "ns per object freed: %llu\n", nr_freed
+		       ? div64_ul(atomic64_read(&shrinker->ns_run), nr_freed)
+		       : 0);
 
 	if (shrinker->to_text) {
 		shrinker->to_text(out, shrinker);
-- 
2.45.2