[PATCH v2 2/2] mm, slab: Show last shrink time in us when slab/shrink is read

[Waiman Long <longman@redhat.com>]

The show method of /sys/kernel/slab/<slab>/shrink sysfs file currently
returns nothing. This is now modified to show the time of the last
cache shrink operation in us.

CONFIG_SLUB_DEBUG depends on CONFIG_SYSFS. So the new shrink_us field
is always available to the shrink methods.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 Documentation/ABI/testing/sysfs-kernel-slab |  2 ++
 include/linux/slub_def.h                    |  1 +
 mm/slub.c                                   | 12 +++++++++---
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-kernel-slab b/Documentation/ABI/testing/sysfs-kernel-slab
index 94ffd47fc8d7..9869a3f57dc3 100644
--- a/Documentation/ABI/testing/sysfs-kernel-slab
+++ b/Documentation/ABI/testing/sysfs-kernel-slab
@@ -437,6 +437,8 @@ Description:
 		write for shrinking the cache. Other input values are
 		considered invalid.  If it is a root cache, all the
 		child memcg caches will also be shrunk, if available.
+		When read, the time in us of the last cache shrink
+		operation is shown.
 
 What:		/sys/kernel/slab/cache/slab_size
 Date:		May 2007
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index d2153789bd9f..055474197e83 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -113,6 +113,7 @@ struct kmem_cache {
 	/* For propagation, maximum size of a stored attr */
 	unsigned int max_attr_size;
 #ifdef CONFIG_SYSFS
+	unsigned int shrink_us;	/* Cache shrink time in us */
 	struct kset *memcg_kset;
 #endif
 #endif
diff --git a/mm/slub.c b/mm/slub.c
index 9736eb10dcb8..77d67a55ce43 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -34,6 +34,7 @@
 #include <linux/prefetch.h>
 #include <linux/memcontrol.h>
 #include <linux/random.h>
+#include <linux/sched/clock.h>
 
 #include <trace/events/kmem.h>
 
@@ -5287,16 +5288,21 @@ SLAB_ATTR(failslab);
 
 static ssize_t shrink_show(struct kmem_cache *s, char *buf)
 {
-	return 0;
+	return sprintf(buf, "%u\n", s->shrink_us);
 }
 
 static ssize_t shrink_store(struct kmem_cache *s,
 			const char *buf, size_t length)
 {
-	if (buf[0] == '1')
+	if (buf[0] == '1') {
+		u64 start = sched_clock();
+
 		kmem_cache_shrink_all(s);
-	else
+		s->shrink_us = (unsigned int)div_u64(sched_clock() - start,
+						     NSEC_PER_USEC);
+	} else {
 		return -EINVAL;
+	}
 	return length;
 }
 SLAB_ATTR(shrink);
-- 
2.18.1