[18/43] xfs: add the zoned space allocator

Commit Message

Christoph Hellwig April 14, 2025, 5:36 a.m. UTC

Source kernel commit: 4e4d52075577707f8393e3fc74c1ef79ca1d3ce6

For zoned RT devices space is always allocated at the write pointer, that
is right after the last written block and only recorded on I/O completion.

Because the actual allocation algorithm is very simple and just involves
picking a good zone - preferably the one used for the last write to the
inode.  As the number of zones that can written at the same time is
usually limited by the hardware, selecting a zone is done as late as
possible from the iomap dio and buffered writeback bio submissions
helpers just before submitting the bio.

Given that the writers already took a reservation before acquiring the
iolock, space will always be readily available if an open zone slot is
available.  A new structure is used to track these open zones, and
pointed to by the xfs_rtgroup.  Because zoned file systems don't have
a rsum cache the space for that pointer can be reused.

Allocations are only recorded at I/O completion time.  The scheme used
for that is very similar to the reflink COW end I/O path.

Co-developed-by: Hans Holmberg <[e-mail]>
Signed-off-by: Hans Holmberg <[e-mail]>
Signed-off-by: Christoph Hellwig <[e-mail]>
Reviewed-by: "Darrick J. Wong" <[e-mail]>
Signed-off-by: Christoph Hellwig <[e-mail]>
---
 libxfs/xfs_rtgroup.h | 22 +++++++++++++++++-----
 libxfs/xfs_types.h   |  1 +
 2 files changed, 18 insertions(+), 5 deletions(-)

Patch

diff --git a/libxfs/xfs_rtgroup.h b/libxfs/xfs_rtgroup.h
index e35d1d798327..5d8777f819f4 100644
--- a/libxfs/xfs_rtgroup.h
+++ b/libxfs/xfs_rtgroup.h
@@ -37,15 +37,27 @@  struct xfs_rtgroup {
 	xfs_rtxnum_t		rtg_extents;
 
 	/*
-	 * Cache of rt summary level per bitmap block with the invariant that
-	 * rtg_rsum_cache[bbno] > the maximum i for which rsum[i][bbno] != 0,
-	 * or 0 if rsum[i][bbno] == 0 for all i.
-	 *
+	 * For bitmap based RT devices this points to a cache of rt summary
+	 * level per bitmap block with the invariant that rtg_rsum_cache[bbno]
+	 * > the maximum i for which rsum[i][bbno] != 0, or 0 if
+	 * rsum[i][bbno] == 0 for all i.
 	 * Reads and writes are serialized by the rsumip inode lock.
+	 *
+	 * For zoned RT devices this points to the open zone structure for
+	 * a group that is open for writers, or is NULL.
 	 */
-	uint8_t			*rtg_rsum_cache;
+	union {
+		uint8_t			*rtg_rsum_cache;
+		struct xfs_open_zone	*rtg_open_zone;
+	};
 };
 
+/*
+ * For zoned RT devices this is set on groups that have no written blocks
+ * and can be picked by the allocator for opening.
+ */
+#define XFS_RTG_FREE			XA_MARK_0
+
 static inline struct xfs_rtgroup *to_rtg(struct xfs_group *xg)
 {
 	return container_of(xg, struct xfs_rtgroup, rtg_group);
diff --git a/libxfs/xfs_types.h b/libxfs/xfs_types.h
index 76f3c31573ec..dc1db15f0be5 100644
--- a/libxfs/xfs_types.h
+++ b/libxfs/xfs_types.h
@@ -243,6 +243,7 @@  enum xfs_free_counter {
 	 * Number of free RT extents on the RT device.
 	 */
 	XC_FREE_RTEXTENTS,
+
 	XC_FREE_NR,
 };