fsnotify: turn fsnotify reaper thread into a workqueue job

We don't require a dedicated thread for fsnotify cleanup.  Switch it
over to a workqueue job instead that runs on the system_unbound_wq.

In the interest of not thrashing the queued job too often when there are
a lot of marks being removed, we delay the reaper job slightly when
queueing it, to allow several to gather on the list.

Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Tested-by: Eryu Guan <guaneryu@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Eric Paris <eparis@parisplace.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 31 deletions

diff --git a/fs/notify/mark.c b/fs/notify/mark.c
index fc0df4442f7b..7115c5d7d373 100644
--- a/fs/notify/mark.c
+++ b/fs/notify/mark.c
@@ -91,10 +91,14 @@
 #include <linux/fsnotify_backend.h>
 #include "fsnotify.h"
 
+#define FSNOTIFY_REAPER_DELAY   (1)     /* 1 jiffy */
+
 struct srcu_struct fsnotify_mark_srcu;
 static DEFINE_SPINLOCK(destroy_lock);
 static LIST_HEAD(destroy_list);
-static DECLARE_WAIT_QUEUE_HEAD(destroy_waitq);
+
+static void fsnotify_mark_destroy(struct work_struct *work);
+static DECLARE_DELAYED_WORK(reaper_work, fsnotify_mark_destroy);
 
 void fsnotify_get_mark(struct fsnotify_mark *mark)
 {
@@ -189,7 +193,8 @@ void fsnotify_free_mark(struct fsnotify_mark *mark)
         spin_lock(&destroy_lock);
         list_add(&mark->g_list, &destroy_list);
         spin_unlock(&destroy_lock);
-        wake_up(&destroy_waitq);
+        queue_delayed_work(system_unbound_wq, &reaper_work,
+                                FSNOTIFY_REAPER_DELAY);
 
         /*
          * Some groups like to know that marks are being freed.  This is a
@@ -388,7 +393,8 @@ err:
         spin_lock(&destroy_lock);
         list_add(&mark->g_list, &destroy_list);
         spin_unlock(&destroy_lock);
-        wake_up(&destroy_waitq);
+        queue_delayed_work(system_unbound_wq, &reaper_work,
+                                FSNOTIFY_REAPER_DELAY);
 
         return ret;
 }
@@ -493,39 +499,20 @@ void fsnotify_init_mark(struct fsnotify_mark *mark,
         mark->free_mark = free_mark;
 }
 
-static int fsnotify_mark_destroy(void *ignored)
+static void fsnotify_mark_destroy(struct work_struct *work)
 {
         struct fsnotify_mark *mark, *next;
         struct list_head private_destroy_list;
 
-        for (;;) {
-                spin_lock(&destroy_lock);
-                /* exchange the list head */
-                list_replace_init(&destroy_list, &private_destroy_list);
-                spin_unlock(&destroy_lock);
-
-                synchronize_srcu(&fsnotify_mark_srcu);
+        spin_lock(&destroy_lock);
+        /* exchange the list head */
+        list_replace_init(&destroy_list, &private_destroy_list);
+        spin_unlock(&destroy_lock);
 
-                list_for_each_entry_safe(mark, next, &private_destroy_list, g_list) {
-                        list_del_init(&mark->g_list);
-                        fsnotify_put_mark(mark);
-                }
+        synchronize_srcu(&fsnotify_mark_srcu);
 
-                wait_event_interruptible(destroy_waitq, !list_empty(&destroy_list));
+        list_for_each_entry_safe(mark, next, &private_destroy_list, g_list) {
+                list_del_init(&mark->g_list);
+                fsnotify_put_mark(mark);
         }
-
-        return 0;
-}
-
-static int __init fsnotify_mark_init(void)
-{
-        struct task_struct *thread;
-
-        thread = kthread_run(fsnotify_mark_destroy, NULL,
-                             "fsnotify_mark");
-        if (IS_ERR(thread))
-                panic("unable to start fsnotify mark destruction thread.");
-
-        return 0;
 }
-device_initcall(fsnotify_mark_init);