UBIFS: slightly optimize write-buffer timer usage

This patch adds the following minor optimization:

1. If write-buffer does not use the timer, indicate it with the
   wbuf->no_timer variable, instead of using the wbuf->softlimit
   variable. This is better because wbuf->softlimit is of ktime_t
   type, and the ktime_to_ns function contains 64-bit multiplication.

2. Do not call the 'hrtimer_cancel()' function for write-buffers
   which do not use timers.

3. Do not cancel the timer in 'ubifs_put_super()' because the
   synchronization function does this.

This patch also removes a confusing comment.
Signed-off-by: NArtem Bityutskiy <Artem.Bityutskiy@nokia.com>

fs/ubifs/io.c

@@ -312,7 +312,7 @@ static void new_wbuf_timer_nolock(struct ubifs_wbuf *wbuf)
 {
 	ubifs_assert(!hrtimer_active(&wbuf->timer));
 
-	if (!ktime_to_ns(wbuf->softlimit))
+	if (wbuf->no_timer)
 		return;
 	dbg_io("set timer for jhead %d, %llu-%llu millisecs", wbuf->jhead,
 	       ktime_to_ns(wbuf->softlimit)/USEC_PER_SEC,
@@ -327,11 +327,8 @@ static void new_wbuf_timer_nolock(struct ubifs_wbuf *wbuf)
  */
 static void cancel_wbuf_timer_nolock(struct ubifs_wbuf *wbuf)
 {
-	/*
-	 * If the syncer is waiting for the lock (from the background thread's
-	 * context) and another task is changing write-buffer then the syncing
-	 * should be canceled.
-	 */
+	if (wbuf->no_timer)
+		return;
 	wbuf->need_sync = 0;
 	hrtimer_cancel(&wbuf->timer);
 }

fs/ubifs/super.c

@@ -797,7 +797,7 @@ static int alloc_wbufs(struct ubifs_info *c)
 	 * does not need to be synchronized by timer.
 	 */
 	c->jheads[GCHD].wbuf.dtype = UBI_LONGTERM;
-	c->jheads[GCHD].wbuf.softlimit = ktime_set(0, 0);
+	c->jheads[GCHD].wbuf.no_timer = 1;
 
 	return 0;
 }
@@ -1754,10 +1754,8 @@ static void ubifs_put_super(struct super_block *sb)
 
 		/* Synchronize write-buffers */
 		if (c->jheads)
-			for (i = 0; i < c->jhead_cnt; i++) {
+			for (i = 0; i < c->jhead_cnt; i++)
 				ubifs_wbuf_sync(&c->jheads[i].wbuf);
-				hrtimer_cancel(&c->jheads[i].wbuf.timer);
-			}
 
 		/*
 		 * On fatal errors c->ro_media is set to 1, in which case we do

fs/ubifs/ubifs.h

@@ -654,7 +654,8 @@ typedef int (*ubifs_lpt_scan_callback)(struct ubifs_info *c,
  * @delta: hard and soft timeouts delta (the timer expire inteval is @softlimit
  *         and @softlimit + @delta)
  * @timer: write-buffer timer
- * @need_sync: it is set if its timer expired and needs sync
+ * @no_timer: non-zero if this write-buffer does not timer
+ * @need_sync: non-zero if its timer expired and needs sync
  * @next_ino: points to the next position of the following inode number
  * @inodes: stores the inode numbers of the nodes which are in wbuf
  *
@@ -683,7 +684,8 @@ struct ubifs_wbuf {
 	ktime_t softlimit;
 	unsigned long long delta;
 	struct hrtimer timer;
-	int need_sync;
+	unsigned int no_timer:1;
+	unsigned int need_sync:1;
 	int next_ino;
 	ino_t *inodes;
 };