XFS: don't block in xfs_qm_dqflush() during async writeback

Normally dquots are written back via delayed write mechanisms. They are flushed to their backing buffer by xfssyncd, which is then pushed out by either AIL or xfsbufd flushing. The flush from the xfssyncd is supposed to be non-blocking, but xfs_qm_dqflush() always waits for pinned duots, which means that it will block for the length of time it takes to do a synchronous log force. This causes unnecessary extra log I/O to be issued whenever we try to flush a busy dquot.

Avoid the log forces and blocking xfssyncd by making xfs_qm_dqflush() pay attention to what type of sync it is doing when it sees a pinned dquot and not waiting when doing non-blocking flushes.

---
 fs/xfs/quota/xfs_dquot.c |   12 +++++-------
 1 files changed, 5 insertions(+), 7 deletions(-)

index 5dca401..591ca66 100644
@@ -1221,16 +1221,14 @@ xfs_qm_dqflush(
 	xfs_dqtrace_entry(dqp, "DQFLUSH");
 
 	/*
-	 * If not dirty, nada.
+	 * If not dirty, or it's pinned and we are not supposed to
+	 * block, nada.
 	 */
-	if (!XFS_DQ_IS_DIRTY(dqp)) {
+	if (!XFS_DQ_IS_DIRTY(dqp) ||
+	    (!(flags & XFS_QMOPT_SYNC) && atomic_read(&dqp->q_pincount) > 0)) {
 		xfs_dqfunlock(dqp);
-		return (0);
+		return 0;
 	}
-
-	/*
-	 * Cant flush a pinned dquot. Wait for it.
-	 */
 	xfs_qm_dqunpin_wait(dqp);
 
 	/*

1.5.6.5

This patch looks good.

Thanks,
Pete