+/*
+ * Wake up bdi's periodically to make sure dirtytime inodes gets
+ * written back periodically. We deliberately do *not* check the
+ * b_dirtytime list in wb_has_dirty_io(), since this would cause the
+ * kernel to be constantly waking up once there are any dirtytime
+ * inodes on the system. So instead we define a separate delayed work
+ * function which gets called much more rarely. (By default, only
+ * once every 12 hours.)
+ *
+ * If there is any other write activity going on in the file system,
+ * this function won't be necessary. But if the only thing that has
+ * happened on the file system is a dirtytime inode caused by an atime
+ * update, we need this infrastructure below to make sure that inode
+ * eventually gets pushed out to disk.
+ */
+static void wakeup_dirtytime_writeback(struct work_struct *w);
+static DECLARE_DELAYED_WORK(dirtytime_work, wakeup_dirtytime_writeback);
+
+static void wakeup_dirtytime_writeback(struct work_struct *w)
+{
+ struct backing_dev_info *bdi;
+
+ rcu_read_lock();
+ list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
+ if (list_empty(&bdi->wb.b_dirty_time))
+ continue;
+ bdi_wakeup_thread(bdi);
+ }
+ rcu_read_unlock();
+ schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
+}
+
+static int __init start_dirtytime_writeback(void)
+{
+ schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
+ return 0;
+}
+__initcall(start_dirtytime_writeback);
+