xfs: don't merge ioends across RTGs

Unlike AGs, RTGs don't always have metadata in their first blocks, and
thus we don't get automatic protection from merging I/O completions
across RTG boundaries.  Add code to set the IOMAP_F_BOUNDARY flag for
ioends that start at the first block of a RTG so that they never get
merged into the previous ioend.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

Author: Darrick J. Wong

fs/xfs/libxfs/xfs_rtgroup.h

@@ -188,6 +188,15 @@ xfs_rtb_to_rgbno(
 	return __xfs_rtb_to_rgbno(mp, rtbno);
 }
 
+/* Is rtbno the start of a RT group? */
+static inline bool
+xfs_rtbno_is_group_start(
+	struct xfs_mount	*mp,
+	xfs_rtblock_t		rtbno)
+{
+	return (rtbno & mp->m_rgblkmask) == 0;
+}
+
 static inline xfs_daddr_t
 xfs_rtb_to_daddr(
 	struct xfs_mount	*mp,

fs/xfs/xfs_iomap.c

@@ -24,6 +24,7 @@
 #include "xfs_iomap.h"
 #include "xfs_trace.h"
 #include "xfs_quota.h"
+#include "xfs_rtgroup.h"
 #include "xfs_dquot_item.h"
 #include "xfs_dquot.h"
 #include "xfs_reflink.h"
@@ -115,7 +116,9 @@ xfs_bmbt_to_iomap(
 		iomap->addr = IOMAP_NULL_ADDR;
 		iomap->type = IOMAP_DELALLOC;
 	} else {
-		iomap->addr = BBTOB(xfs_fsb_to_db(ip, imap->br_startblock));
+		xfs_daddr_t	daddr = xfs_fsb_to_db(ip, imap->br_startblock);
+
+		iomap->addr = BBTOB(daddr);
 		if (mapping_flags & IOMAP_DAX)
 			iomap->addr += target->bt_dax_part_off;
 
@@ -124,6 +127,14 @@ xfs_bmbt_to_iomap(
 		else
 			iomap->type = IOMAP_MAPPED;
 
+		/*
+		 * Mark iomaps starting at the first sector of a RTG as merge
+		 * boundary so that each I/O completions is contained to a
+		 * single RTG.
+		 */
+		if (XFS_IS_REALTIME_INODE(ip) && xfs_has_rtgroups(mp) &&
+		    xfs_rtbno_is_group_start(mp, imap->br_startblock))
+			iomap->flags |= IOMAP_F_BOUNDARY;
 	}
 	iomap->offset = XFS_FSB_TO_B(mp, imap->br_startoff);
 	iomap->length = XFS_FSB_TO_B(mp, imap->br_blockcount);