[PATCH 3/3] xfs: set s_min_writeback_pages for zoned file systems

[Christoph Hellwig <hch@lst.de>]

Set s_min_writeback_pages to the zone size, so that writeback always
writes up to a full zone.  This ensures that writeback does not add
spurious file fragmentation when writing back a large number of
files that are larger than the zone size.

Fixes: 4e4d52075577 ("xfs: add the zoned space allocator")
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/xfs/xfs_zone_alloc.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_zone_alloc.c b/fs/xfs/xfs_zone_alloc.c
index 1147bacb2da8..0f4e460fd3ea 100644
--- a/fs/xfs/xfs_zone_alloc.c
+++ b/fs/xfs/xfs_zone_alloc.c
@@ -1215,6 +1215,7 @@ xfs_mount_zones(
 		.mp		= mp,
 	};
 	struct xfs_buftarg	*bt = mp->m_rtdev_targp;
+	xfs_extlen_t		zone_blocks = mp->m_groups[XG_TYPE_RTG].blocks;
 	int			error;
 
 	if (!bt) {
@@ -1245,10 +1246,12 @@ xfs_mount_zones(
 		return -ENOMEM;
 
 	xfs_info(mp, "%u zones of %u blocks (%u max open zones)",
-		 mp->m_sb.sb_rgcount, mp->m_groups[XG_TYPE_RTG].blocks,
-		 mp->m_max_open_zones);
+		 mp->m_sb.sb_rgcount, zone_blocks, mp->m_max_open_zones);
 	trace_xfs_zones_mount(mp);
 
+	mp->m_super->s_min_writeback_pages =
+		XFS_FSB_TO_B(mp, zone_blocks) >> PAGE_SHIFT;
+
 	if (bdev_is_zoned(bt->bt_bdev)) {
 		error = blkdev_report_zones(bt->bt_bdev,
 				XFS_FSB_TO_BB(mp, mp->m_sb.sb_rtstart),
-- 
2.47.3