linux-kernel - [PATCH 3/7] mm: shrinker: Add new stats for .to

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Date:   Wed, 22 Nov 2023 18:25:08 -0500
From:   Kent Overstreet <kent.overstreet@...ux.dev>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Kent Overstreet <kent.overstreet@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>
Subject: [PATCH 3/7] mm: shrinker: Add new stats for .to_text()

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@...ux-foundation.org>
Cc: Qi Zheng <zhengqi.arch@...edance.com>
Cc: Roman Gushchin <roman.gushchin@...ux.dev>
Cc: linux-mm@...ck.org
Signed-off-by: Kent Overstreet <kent.overstreet@...ux.dev>
---
 include/linux/shrinker.h |  5 +++++
 mm/shrinker.c            | 18 +++++++++++++++++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 968c55474e78..497a7e8e348c 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -118,6 +118,11 @@ 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;
+	atomic_long_t last_freed;
+	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 4976dbac4c83..acfc3f92f552 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -430,13 +430,20 @@ 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;
+		atomic_long_add(ret, &shrinker->objects_freed);
+		atomic_long_set(&shrinker->last_freed, ret);
 
 		count_vm_events(SLABS_SCANNED, shrinkctl->nr_scanned);
 		total_scan -= shrinkctl->nr_scanned;
@@ -812,9 +819,18 @@ 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", shrinker->count_objects(shrinker, &sc));
+	seq_buf_printf(out, "requested to free:   %lu", atomic_long_read(&shrinker->objects_requested_to_free));
+	seq_buf_printf(out, "objects freed:       %lu", nr_freed);
+	seq_buf_printf(out, "last freed:          %lu", atomic_long_read(&shrinker->last_freed));
+	seq_buf_printf(out, "ns per object freed: %llu", nr_freed
+		       ? div64_ul(atomic64_read(&shrinker->ns_run), nr_freed)
+		       : 0);
 
 	if (shrinker->to_text) {
 		shrinker->to_text(out, shrinker);
-- 
2.42.0