xfs: xfs_iflush() is no longer necessary

Now we have a cached buffer on inode log items, we don't need
to do buffer lookups when flushing inodes anymore - all we need
to do is lock the buffer and we are ready to go.

This largely gets rid of the need for xfs_iflush(), which is
essentially just a mechanism to look up the buffer and flush the
inode to it. Instead, we can just call xfs_iflush_cluster() with a
few modifications to ensure it also flushes the inode we already
hold locked.

This allows the AIL inode item pushing to be almost entirely
non-blocking in XFS - we won't block unless memory allocation
for the cluster inode lookup blocks or the block device queues are
full.

Writeback during inode reclaim becomes a little more complex because
we now have to lock the buffer ourselves, but otherwise this change
is largely a functional no-op that removes a whole lot of code.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

1 files changed, 18 insertions, 33 deletions

diff --git a/fs/xfs/xfs_inode_item.c b/fs/xfs/xfs_inode_item.c
index 697248b7eb2b..e8eda2ac25fb 100644
--- a/fs/xfs/xfs_inode_item.c
+++ b/fs/xfs/xfs_inode_item.c
@@ -485,53 +485,38 @@ xfs_inode_item_push(
 	uint			rval = XFS_ITEM_SUCCESS;
 	int			error;
 
-	if (xfs_ipincount(ip) > 0)
+	ASSERT(iip->ili_item.li_buf);
+
+	if (xfs_ipincount(ip) > 0 || xfs_buf_ispinned(bp) ||
+	    (ip->i_flags & XFS_ISTALE))
 		return XFS_ITEM_PINNED;
 
-	if (!xfs_ilock_nowait(ip, XFS_ILOCK_SHARED))
-		return XFS_ITEM_LOCKED;
+	/* If the inode is already flush locked, we're already flushing. */
+	if (xfs_isiflocked(ip))
+		return XFS_ITEM_FLUSHING;
 
-	/*
-	 * Re-check the pincount now that we stabilized the value by
-	 * taking the ilock.
-	 */
-	if (xfs_ipincount(ip) > 0) {
-		rval = XFS_ITEM_PINNED;
-		goto out_unlock;
-	}
+	if (!xfs_buf_trylock(bp))
+		return XFS_ITEM_LOCKED;
 
-	/*
-	 * Stale inode items should force out the iclog.
-	 */
-	if (ip->i_flags & XFS_ISTALE) {
-		rval = XFS_ITEM_PINNED;
-		goto out_unlock;
-	}
+	spin_unlock(&lip->li_ailp->ail_lock);
 
 	/*
-	 * Someone else is already flushing the inode.  Nothing we can do
-	 * here but wait for the flush to finish and remove the item from
-	 * the AIL.
+	 * We need to hold a reference for flushing the cluster buffer as it may
+	 * fail the buffer without IO submission. In which case, we better get a
+	 * reference for that completion because otherwise we don't get a
+	 * reference for IO until we queue the buffer for delwri submission.
 	 */
-	if (!xfs_iflock_nowait(ip)) {
-		rval = XFS_ITEM_FLUSHING;
-		goto out_unlock;
-	}
-
-	ASSERT(iip->ili_fields != 0 || XFS_FORCED_SHUTDOWN(ip->i_mount));
-	spin_unlock(&lip->li_ailp->ail_lock);
-
-	error = xfs_iflush(ip, &bp);
+	xfs_buf_hold(bp);
+	error = xfs_iflush_cluster(ip, bp);
 	if (!error) {
 		if (!xfs_buf_delwri_queue(bp, buffer_list))
 			rval = XFS_ITEM_FLUSHING;
 		xfs_buf_relse(bp);
-	} else if (error == -EAGAIN)
+	} else {
 		rval = XFS_ITEM_LOCKED;
+	}
 
 	spin_lock(&lip->li_ailp->ail_lock);
-out_unlock:
-	xfs_iunlock(ip, XFS_ILOCK_SHARED);
 	return rval;
 }