From: Darrick J. Wong <djwong@kernel.org>

If a fs modification (creation, file write, reflink, etc.) is unable to
reserve enough space to handle the modification, try clearing whatever
space the filesystem might have been hanging onto in the hopes of
speeding up the filesystem.  The flushing behavior will become
particularly important when we add deferred inode inactivation because
that will increase the amount of space that isn't actively tied to user
data.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 fs/xfs/xfs_trans.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index b08bb5a8fb60..3c2b26a21c6d 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c

@@ -289,6 +289,18 @@ xfs_trans_alloc(
 	tp->t_firstblock = NULLFSBLOCK;
 
 	error = xfs_trans_reserve(tp, resp, blocks, rtextents);
+	if (error == -ENOSPC) {
+		/*
+		 * We weren't able to reserve enough space for the transaction.
+		 * Flush the other speculative space allocations to free space.
+		 * Do not perform a synchronous scan because callers can hold
+		 * other locks.
+		 */
+		error = xfs_blockgc_free_space(mp, NULL);
+		if (error)
+			return error;
+		error = xfs_trans_reserve(tp, resp, blocks, rtextents);
+	}
 	if (error) {
 		xfs_trans_cancel(tp);
 		return error;