fsnotify: Free fsnotify_mark_connector when there is no mark attached

Currently we free fsnotify_mark_connector structure only when inode /
vfsmount is getting freed. This can however impose noticeable memory
overhead when marks get attached to inodes only temporarily. So free the
connector structure once the last mark is detached from the object.
Since notification infrastructure can be working with the connector
under the protection of fsnotify_mark_srcu, we have to be careful and
free the fsnotify_mark_connector only after SRCU period passes.

Reviewed-by: Miklos Szeredi <mszeredi@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 7 insertions, 4 deletions

diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 02c6fac652a4..84d71b6f75f6 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -197,8 +197,8 @@ struct fsnotify_group {
 /*
  * Inode / vfsmount point to this structure which tracks all marks attached to
  * the inode / vfsmount. The reference to inode / vfsmount is held by this
- * structure whenever the list is non-empty. The structure is freed only when
- * inode / vfsmount gets freed.
+ * structure. We destroy this structure when there are no more marks attached
+ * to it. The structure is protected by fsnotify_mark_srcu.
  */
 struct fsnotify_mark_connector {
 	spinlock_t lock;
@@ -209,7 +209,11 @@ struct fsnotify_mark_connector {
 		struct inode *inode;
 		struct vfsmount *mnt;
 	};
-	struct hlist_head list;
+	union {
+		struct hlist_head list;
+		/* Used listing heads to free after srcu period expires */
+		struct fsnotify_mark_connector *destroy_next;
+	};
 };
 
 /*
@@ -361,7 +365,6 @@ extern void fsnotify_clear_vfsmount_marks_by_group(struct fsnotify_group *group)
 extern void fsnotify_clear_inode_marks_by_group(struct fsnotify_group *group);
 /* run all the marks in a group, and clear all of the marks attached to given object type */
 extern void fsnotify_clear_marks_by_group_flags(struct fsnotify_group *group, unsigned int flags);
-extern void fsnotify_connector_free(struct fsnotify_mark_connector **connp);
 extern void fsnotify_get_mark(struct fsnotify_mark *mark);
 extern void fsnotify_put_mark(struct fsnotify_mark *mark);
 extern void fsnotify_unmount_inodes(struct super_block *sb);