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

If a fs modification (creation, file write, reflink, etc.) is unable to
reserve enough quota 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>
---
 fs/xfs/xfs_bmap_util.c |   16 ++++++++++++++++
 fs/xfs/xfs_file.c      |    2 +-
 fs/xfs/xfs_icache.c    |    9 +++++++--
 fs/xfs/xfs_icache.h    |    2 +-
 fs/xfs/xfs_inode.c     |   17 +++++++++++++++++
 fs/xfs/xfs_ioctl.c     |    2 ++
 fs/xfs/xfs_iomap.c     |   20 +++++++++++++++++++-
 fs/xfs/xfs_reflink.c   |   40 +++++++++++++++++++++++++++++++++++++---
 fs/xfs/xfs_trace.c     |    1 +
 fs/xfs/xfs_trace.h     |   40 ++++++++++++++++++++++++++++++++++++++++
 10 files changed, 141 insertions(+), 8 deletions(-)

diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index 7371a7f7c652..437fdc8a8fbd 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c

@@ -761,6 +761,7 @@ xfs_alloc_file_space(
 	 */
 	while (allocatesize_fsb && !error) {
 		xfs_fileoff_t	s, e;
+		bool		cleared_space = false;
 
 		/*
 		 * Determine space reservations for data/realtime.

@@ -803,6 +804,7 @@ xfs_alloc_file_space(
 		/*
 		 * Allocate and setup the transaction.
 		 */
+retry:
 		error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks,
 				resrtextents, 0, &tp);
 

@@ -819,6 +821,20 @@ xfs_alloc_file_space(
 		xfs_ilock(ip, XFS_ILOCK_EXCL);
 		error = xfs_trans_reserve_quota_nblks(tp, ip, qblocks,
 						      0, quota_flag);
+		/*
+		 * We weren't able to reserve enough quota to handle fallocate.
+		 * Flush any disk space that was being held in the hopes of
+		 * speeding up the filesystem.  We hold the IOLOCK so we cannot
+		 * do a synchronous scan.
+		 */
+		if ((error == -ENOSPC || error == -EDQUOT) && !cleared_space) {
+			xfs_trans_cancel(tp);
+			xfs_iunlock(ip, XFS_ILOCK_EXCL);
+			cleared_space = xfs_inode_free_quota_blocks(ip, false);
+			if (cleared_space)
+				goto retry;
+			return error;