xfs: implement freezing by emptying the AIL

Now that we write back all metadata either synchronously or through
the AIL we can simply implement metadata freezing in terms of
emptying the AIL.

The implementation for this is fairly simply and straight-forward:
A new routine is added that asks the xfsaild to push the AIL to the
end and waits for it to complete and send a wakeup. The routine will
then loop if the AIL is not actually empty, and continue to do so
until the AIL is compeltely empty.

We keep an inode reclaim pass in the freeze process to avoid having
memory pressure have to reclaim inodes that require dirtying the
filesystem to be reclaimed after the freeze has completed. This
means we can also treat unmount in the exact same way as freeze.

As an upside we can now remove the radix tree based inode writeback
and xfs_unmountfs_writesb.

[ Dave Chinner:
	- Cleaned up commit message.
	- Added inode reclaim passes back into freeze.
	- Cleaned up wakeup mechanism to avoid the use of a new
	  sleep counter variable. ]

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

1 files changed, 29 insertions, 7 deletions

diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c
index 77acc53f2f3..0425ca16738 100644
--- a/fs/xfs/xfs_trans_ail.c
+++ b/fs/xfs/xfs_trans_ail.c
@@ -383,9 +383,8 @@ xfsaild_push(
 		spin_lock(&ailp->xa_lock);
 	}
 
-	target = ailp->xa_target;
 	lip = xfs_trans_ail_cursor_first(ailp, &cur, ailp->xa_last_pushed_lsn);
-	if (!lip || XFS_FORCED_SHUTDOWN(mp)) {
+	if (!lip) {
 		/*
 		 * AIL is empty or our push has reached the end.
 		 */
@@ -408,6 +407,7 @@ xfsaild_push(
 	 * lots of contention on the AIL lists.
 	 */
 	lsn = lip->li_lsn;
+	target = ailp->xa_target;
 	while ((XFS_LSN_CMP(lip->li_lsn, target) <= 0)) {
 		int	lock_result;
 		/*
@@ -466,11 +466,6 @@ xfsaild_push(
 		}
 
 		spin_lock(&ailp->xa_lock);
-		/* should we bother continuing? */
-		if (XFS_FORCED_SHUTDOWN(mp))
-			break;
-		ASSERT(mp->m_log);
-
 		count++;
 
 		/*
@@ -611,6 +606,30 @@ xfs_ail_push_all(
 }
 
 /*
+ * Push out all items in the AIL immediately and wait until the AIL is empty.
+ */
+void
+xfs_ail_push_all_sync(
+	struct xfs_ail  *ailp)
+{
+	struct xfs_log_item	*lip;
+	DEFINE_WAIT(wait);
+
+	spin_lock(&ailp->xa_lock);
+	while ((lip = xfs_ail_max(ailp)) != NULL) {
+		prepare_to_wait(&ailp->xa_empty, &wait, TASK_UNINTERRUPTIBLE);
+		ailp->xa_target = lip->li_lsn;
+		wake_up_process(ailp->xa_task);
+		spin_unlock(&ailp->xa_lock);
+		schedule();
+		spin_lock(&ailp->xa_lock);
+	}
+	spin_unlock(&ailp->xa_lock);
+
+	finish_wait(&ailp->xa_empty, &wait);
+}
+
+/*
  * xfs_trans_ail_update - bulk AIL insertion operation.
  *
  * @xfs_trans_ail_update takes an array of log items that all need to be
@@ -737,6 +756,8 @@ xfs_trans_ail_delete_bulk(
 	if (mlip_changed) {
 		if (!XFS_FORCED_SHUTDOWN(ailp->xa_mount))
 			xlog_assign_tail_lsn_locked(ailp->xa_mount);
+		if (list_empty(&ailp->xa_ail))
+			wake_up_all(&ailp->xa_empty);
 		spin_unlock(&ailp->xa_lock);
 
 		xfs_log_space_wake(ailp->xa_mount);
@@ -773,6 +794,7 @@ xfs_trans_ail_init(
 	INIT_LIST_HEAD(&ailp->xa_ail);
 	INIT_LIST_HEAD(&ailp->xa_cursors);
 	spin_lock_init(&ailp->xa_lock);
+	init_waitqueue_head(&ailp->xa_empty);
 
 	ailp->xa_task = kthread_run(xfsaild, ailp, "xfsaild/%s",
 			ailp->xa_mount->m_fsname);