fsnotify: use hash table for faster events merge

In order to improve event merge performance, hash events in a 128 size
hash table by the event merge key.

The fanotify_event size grows by two pointers, but we just reduced its
size by removing the objectid member, so overall its size is increased
by one pointer.

Permission events and overflow event are not merged so they are also
not hashed.

Link: https://lore.kernel.org/r/20210304104826.3993892-5-amir73il@gmail.com
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 15 insertions, 7 deletions

diff --git a/fs/notify/notification.c b/fs/notify/notification.c
index 001cfe7d2e4e..32f45543b9c6 100644
--- a/fs/notify/notification.c
+++ b/fs/notify/notification.c
@@ -68,16 +68,22 @@ void fsnotify_destroy_event(struct fsnotify_group *group,
 }
 
 /*
- * Add an event to the group notification queue.  The group can later pull this
- * event off the queue to deal with.  The function returns 0 if the event was
- * added to the queue, 1 if the event was merged with some other queued event,
+ * Try to add an event to the notification queue.
+ * The group can later pull this event off the queue to deal with.
+ * The group can use the @merge hook to merge the event with a queued event.
+ * The group can use the @insert hook to insert the event into hash table.
+ * The function returns:
+ * 0 if the event was added to a queue
+ * 1 if the event was merged with some other queued event
  * 2 if the event was not queued - either the queue of events has overflown
- * or the group is shutting down.
+ *   or the group is shutting down.
  */
 int fsnotify_add_event(struct fsnotify_group *group,
 		       struct fsnotify_event *event,
-		       int (*merge)(struct list_head *,
-				    struct fsnotify_event *))
+		       int (*merge)(struct fsnotify_group *,
+				    struct fsnotify_event *),
+		       void (*insert)(struct fsnotify_group *,
+				      struct fsnotify_event *))
 {
 	int ret = 0;
 	struct list_head *list = &group->notification_list;
@@ -104,7 +110,7 @@ int fsnotify_add_event(struct fsnotify_group *group,
 	}
 
 	if (!list_empty(list) && merge) {
-		ret = merge(list, event);
+		ret = merge(group, event);
 		if (ret) {
 			spin_unlock(&group->notification_lock);
 			return ret;
@@ -114,6 +120,8 @@ int fsnotify_add_event(struct fsnotify_group *group,
 queue:
 	group->q_len++;
 	list_add_tail(&event->list, list);
+	if (insert)
+		insert(group, event);
 	spin_unlock(&group->notification_lock);
 
 	wake_up(&group->notification_waitq);