diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index 1853797ea938..3e8eedf01eb2 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -425,30 +425,6 @@ xfs_update_alignment(xfs_mount_t *mp)
 	return 0;
 }
 
-/*
- * Set the default minimum read and write sizes unless
- * already specified in a mount option.
- * We use smaller I/O sizes when the file system
- * is being used for NFS service (wsync mount option).
- */
-STATIC void
-xfs_set_rw_sizes(xfs_mount_t *mp)
-{
-	xfs_sb_t	*sbp = &(mp->m_sb);
-	int		readio_log, writeio_log;
-
-	if (!(mp->m_flags & XFS_MOUNT_DFLT_IOSIZE))
-		writeio_log = XFS_WRITEIO_LOG_LARGE;
-	else
-		writeio_log = mp->m_allocsize_log;
-
-	if (sbp->sb_blocklog > writeio_log)
-		mp->m_allocsize_log = sbp->sb_blocklog;
-	} else
-		mp->m_allocsize_log = writeio_log;
-	mp->m_allocsize_blocks = 1 << (mp->m_allocsize_log - sbp->sb_blocklog);
-}
-
 /*
  * precalculate the low space thresholds for dynamic speculative preallocation.
  */
@@ -713,9 +689,12 @@ xfs_mountfs(
 		goto out_remove_errortag;
 
 	/*
-	 * Set the minimum read and write sizes
+	 * Update the preferred write size based on the information from the
+	 * on-disk superblock.
 	 */
-	xfs_set_rw_sizes(mp);
+	mp->m_allocsize_log =
+		max_t(uint32_t, sbp->sb_blocklog, mp->m_allocsize_log);
+	mp->m_allocsize_blocks = 1U << (mp->m_allocsize_log - sbp->sb_blocklog);
 
 	/* set the low space thresholds for dynamic preallocation */
 	xfs_set_low_space_thresholds(mp);
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 109081c16a07..712dbb2039cd 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -244,12 +244,6 @@ typedef struct xfs_mount {
 
 #define XFS_MOUNT_DAX		(1ULL << 62)	/* TEST ONLY! */
 
-
-/*
- * Default write size.
- */
-#define XFS_WRITEIO_LOG_LARGE	16
-
 /*
  * Max and min values for mount-option defined I/O
  * preallocation sizes.
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index d1a0958f336d..3e5002d2a79e 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -159,8 +159,7 @@ xfs_parseargs(
 	const struct super_block *sb = mp->m_super;
 	char			*p;
 	substring_t		args[MAX_OPT_ARGS];
-	int			iosize = 0;
-	uint8_t			iosizelog = 0;
+	int			size = 0;
 
 	/*
 	 * set up the mount name first so all the errors will refer to the
@@ -192,6 +191,7 @@ xfs_parseargs(
 	 */
 	mp->m_logbufs = -1;
 	mp->m_logbsize = -1;
+	mp->m_allocsize_log = 16; /* 64k */
 
 	if (!options)
 		goto done;
@@ -225,9 +225,10 @@ xfs_parseargs(
 				return -ENOMEM;
 			break;
 		case Opt_allocsize:
-			if (suffix_kstrtoint(args, 10, &iosize))
+			if (suffix_kstrtoint(args, 10, &size))
 				return -EINVAL;
-			iosizelog = ffs(iosize) - 1;
+			mp->m_allocsize_log = ffs(size) - 1;
+			mp->m_flags |= XFS_MOUNT_DFLT_IOSIZE;
 			break;
 		case Opt_grpid:
 		case Opt_bsdgroups:
@@ -395,17 +396,12 @@ done:
 		return -EINVAL;
 	}
 
-	if (iosizelog) {
-		if (iosizelog > XFS_MAX_IO_LOG ||
-		    iosizelog < XFS_MIN_IO_LOG) {
-			xfs_warn(mp, "invalid log iosize: %d [not %d-%d]",
-				iosizelog, XFS_MIN_IO_LOG,
-				XFS_MAX_IO_LOG);
-			return -EINVAL;
-		}
-
-		mp->m_flags |= XFS_MOUNT_DFLT_IOSIZE;
-		mp->m_allocsize_log = iosizelog;
+	if ((mp->m_flags & XFS_MOUNT_DFLT_IOSIZE) &&
+	    (mp->m_allocsize_log > XFS_MAX_IO_LOG ||
+	     mp->m_allocsize_log < XFS_MIN_IO_LOG)) {
+		xfs_warn(mp, "invalid log iosize: %d [not %d-%d]",
+			mp->m_allocsize_log, XFS_MIN_IO_LOG, XFS_MAX_IO_LOG);
+		return -EINVAL;
 	}
 
 	return 0;