fsnotify: optimize the case of no permission event watchers

Commit e43de7f0862b ("fsnotify: optimize the case of no marks of any type")
optimized the case where there are no fsnotify watchers on any of the
filesystem's objects.

It is quite common for a system to have a single local filesystem and
it is quite common for the system to have some inotify watches on some
config files or directories, so the optimization of no marks at all is
often not in effect.

Permission event watchers, which require high priority group are more
rare, so optimizing the case of no marks og high priority groups can
improve performance for more systems, especially for performance
sensitive io workloads.

Count per-sb watched objects by high priority groups and use that the
optimize out the call to __fsnotify_parent() and fsnotify() in fsnotify
permission hooks.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <20240317184154.1200192-11-amir73il@gmail.com>

2 files changed, 30 insertions, 3 deletions

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index fb3f36bc6ea9..2ae965ef37e8 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -100,6 +100,9 @@ void fsnotify_sb_delete(struct super_block *sb)
 	/* Wait for outstanding object references from connectors */
 	wait_var_event(fsnotify_sb_watched_objects(sb),
 		       !atomic_long_read(fsnotify_sb_watched_objects(sb)));
+	WARN_ON(fsnotify_sb_has_priority_watchers(sb, FSNOTIFY_PRIO_CONTENT));
+	WARN_ON(fsnotify_sb_has_priority_watchers(sb,
+						  FSNOTIFY_PRIO_PRE_CONTENT));
 	kfree(sbinfo);
 }
 
diff --git a/fs/notify/mark.c b/fs/notify/mark.c
index b2f5d8c9cce1..c3eefa70633c 100644
--- a/fs/notify/mark.c
+++ b/fs/notify/mark.c
@@ -161,13 +161,36 @@ static void fsnotify_put_inode_ref(struct inode *inode)
 static void fsnotify_update_sb_watchers(struct super_block *sb,
 					struct fsnotify_mark_connector *conn)
 {
+	struct fsnotify_sb_info *sbinfo = fsnotify_sb_info(sb);
 	bool is_watched = conn->flags & FSNOTIFY_CONN_FLAG_IS_WATCHED;
-	bool has_marks = conn->obj && !hlist_empty(&conn->list);
+	struct fsnotify_mark *first_mark = NULL;
+	unsigned int highest_prio = 0;
 
-	if (has_marks && !is_watched) {
+	if (conn->obj)
+		first_mark = hlist_entry_safe(conn->list.first,
+					      struct fsnotify_mark, obj_list);
+	if (first_mark)
+		highest_prio = first_mark->group->priority;
+	if (WARN_ON(highest_prio >= __FSNOTIFY_PRIO_NUM))
+		highest_prio = 0;
+
+	/*
+	 * If the highest priority of group watching this object is prio,
+	 * then watched object has a reference on counters [0..prio].
+	 * Update priority >= 1 watched objects counters.
+	 */
+	for (unsigned int p = conn->prio + 1; p <= highest_prio; p++)
+		atomic_long_inc(&sbinfo->watched_objects[p]);
+	for (unsigned int p = conn->prio; p > highest_prio; p--)
+		atomic_long_dec(&sbinfo->watched_objects[p]);
+	conn->prio = highest_prio;
+
+	/* Update priority >= 0 (a.k.a total) watched objects counter */
+	BUILD_BUG_ON(FSNOTIFY_PRIO_NORMAL != 0);
+	if (first_mark && !is_watched) {
 		conn->flags |= FSNOTIFY_CONN_FLAG_IS_WATCHED;
 		fsnotify_get_sb_watched_objects(sb);
-	} else if (!has_marks && is_watched) {
+	} else if (!first_mark && is_watched) {
 		conn->flags &= ~FSNOTIFY_CONN_FLAG_IS_WATCHED;
 		fsnotify_put_sb_watched_objects(sb);
 	}
@@ -600,6 +623,7 @@ static int fsnotify_attach_connector_to_object(fsnotify_connp_t *connp,
 	spin_lock_init(&conn->lock);
 	INIT_HLIST_HEAD(&conn->list);
 	conn->flags = 0;
+	conn->prio = 0;
 	conn->type = obj_type;
 	conn->obj = obj;