Merge tag 'vfs-6.19-rc1.writeback' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull writeback updates from Christian Brauner:
 "Features:

   - Allow file systems to increase the minimum writeback chunk size.

     The relatively low minimal writeback size of 4MiB means that
     written back inodes on rotational media are switched a lot. Besides
     introducing additional seeks, this also can lead to extreme file
     fragmentation on zoned devices when a lot of files are cached
     relative to the available writeback bandwidth.

     This adds a superblock field that allows the file system to
     override the default size, and sets it to the zone size for zoned
     XFS.

   - Add logging for slow writeback when it exceeds
     sysctl_hung_task_timeout_secs. This helps identify tasks waiting
     for a long time and pinpoint potential issues. Recording the
     starting jiffies is also useful when debugging a crashed vmcore.

   - Wake up waiting tasks when finishing the writeback of a chunk

  Cleanups:

   - filemap_* writeback interface cleanups.

     Adding filemap_fdatawrite_wbc ended up being a mistake, as all but
     the original btrfs caller should be using better high level
     interfaces instead.

     This series removes all these low-level interfaces, switches btrfs
     to a more specific interface, and cleans up other too low-level
     interfaces. With this the writeback_control that is passed to the
     writeback code is only initialized in three places.

   - Remove __filemap_fdatawrite, __filemap_fdatawrite_range, and
     filemap_fdatawrite_wbc

   - Add filemap_flush_nr helper for btrfs

   - Push struct writeback_control into start_delalloc_inodes in btrfs

   - Rename filemap_fdatawrite_range_kick to filemap_flush_range

   - Stop opencoding filemap_fdatawrite_range in 9p, ocfs2, and mm

   - Make wbc_to_tag() inline and use it in fs"

* tag 'vfs-6.19-rc1.writeback' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  fs: Make wbc_to_tag() inline and use it in fs.
  xfs: set s_min_writeback_pages for zoned file systems
  writeback: allow the file system to override MIN_WRITEBACK_PAGES
  writeback: cleanup writeback_chunk_size
  mm: rename filemap_fdatawrite_range_kick to filemap_flush_range
  mm: remove __filemap_fdatawrite_range
  mm: remove filemap_fdatawrite_wbc
  mm: remove __filemap_fdatawrite
  mm,btrfs: add a filemap_flush_nr helper
  btrfs: push struct writeback_control into start_delalloc_inodes
  btrfs: use the local tmp_inode variable in start_delalloc_inodes
  ocfs2: don't opencode filemap_fdatawrite_range in ocfs2_journal_submit_inode_data_buffers
  9p: don't opencode filemap_fdatawrite_range in v9fs_mmap_vm_close
  mm: don't opencode filemap_fdatawrite_range in filemap_invalidate_inode
  writeback: Add logging for slow writeback (exceeds sysctl_hung_task_timeout_secs)
  writeback: Wake up waiting tasks when finishing the writeback of a chunk.

1 files changed, 26 insertions, 2 deletions

diff --git a/fs/xfs/xfs_zone_alloc.c b/fs/xfs/xfs_zone_alloc.c
index ef7a931ebde5..8dde444596f1 100644
--- a/fs/xfs/xfs_zone_alloc.c
+++ b/fs/xfs/xfs_zone_alloc.c
@@ -1204,6 +1204,7 @@ 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) {
@@ -1234,10 +1235,33 @@ 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);
 
+	/*
+	 * The writeback code switches between inodes regularly to provide
+	 * fairness.  The default lower bound is 4MiB, but for zoned file
+	 * systems we want to increase that both to reduce seeks, but also more
+	 * importantly so that workloads that writes files in a multiple of the
+	 * zone size do not get fragmented and require garbage collection when
+	 * they shouldn't.  Increase is to the zone size capped by the max
+	 * extent len.
+	 *
+	 * Note that because s_min_writeback_pages is a superblock field, this
+	 * value also get applied to non-zoned files on the data device if
+	 * there are any.  On typical zoned setup all data is on the RT device
+	 * because using the more efficient sequential write required zones
+	 * is the reason for using the zone allocator, and either the RT device
+	 * and the (meta)data device are on the same block device, or the
+	 * (meta)data device is on a fast SSD while the data on the RT device
+	 * is on a SMR HDD.  In any combination of the above cases enforcing
+	 * the higher min_writeback_pages for non-RT inodes is either a noop
+	 * or beneficial.
+	 */
+	mp->m_super->s_min_writeback_pages =
+		XFS_FSB_TO_B(mp, min(zone_blocks, XFS_MAX_BMBT_EXTLEN)) >>
+			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),