xfs: allow sysadmins to specify a maximum atomic write limit at mount time

Introduce a mount option to allow sysadmins to specify the maximum size
of an atomic write.  If the filesystem can work with the supplied value,
that becomes the new guaranteed maximum.

The value mustn't be too big for the existing filesystem geometry (max
write size, max AG/rtgroup size).  We dynamically recompute the
tr_atomic_write transaction reservation based on the given block size,
check that the current log size isn't less than the new minimum log size
constraints, and set a new maximum.

The actual software atomic write max is still computed based off of
tr_atomic_ioend the same way it has for the past few commits.  Note also
that xfs_calc_atomic_write_log_geometry is non-static because mkfs will
need that.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: John Garry <john.g.garry@oracle.com>

2 files changed, 73 insertions, 0 deletions

diff --git a/fs/xfs/libxfs/xfs_trans_resv.c b/fs/xfs/libxfs/xfs_trans_resv.c
index e73c09fbd24c..86a111d0f2fc 100644
--- a/fs/xfs/libxfs/xfs_trans_resv.c
+++ b/fs/xfs/libxfs/xfs_trans_resv.c
@@ -1488,3 +1488,72 @@ xfs_calc_max_atomic_write_fsblocks(
 
 	return ret;
 }
+
+/*
+ * Compute the log blocks and transaction reservation needed to complete an
+ * atomic write of a given number of blocks.  Worst case, each block requires
+ * separate handling.  A return value of 0 means something went wrong.
+ */
+xfs_extlen_t
+xfs_calc_atomic_write_log_geometry(
+	struct xfs_mount	*mp,
+	xfs_extlen_t		blockcount,
+	unsigned int		*new_logres)
+{
+	struct xfs_trans_res	*curr_res = &M_RES(mp)->tr_atomic_ioend;
+	uint			old_logres = curr_res->tr_logres;
+	unsigned int		per_intent, step_size;
+	unsigned int		logres;
+	xfs_extlen_t		min_logblocks;
+
+	ASSERT(blockcount > 0);
+
+	xfs_calc_default_atomic_ioend_reservation(mp, M_RES(mp));
+
+	per_intent = xfs_calc_atomic_write_ioend_geometry(mp, &step_size);
+
+	/* Check for overflows */
+	if (check_mul_overflow(blockcount, per_intent, &logres) ||
+	    check_add_overflow(logres, step_size, &logres))
+		return 0;
+
+	curr_res->tr_logres = logres;
+	min_logblocks = xfs_log_calc_minimum_size(mp);
+	curr_res->tr_logres = old_logres;
+
+	trace_xfs_calc_max_atomic_write_log_geometry(mp, per_intent, step_size,
+			blockcount, min_logblocks, logres);
+
+	*new_logres = logres;
+	return min_logblocks;
+}
+
+/*
+ * Compute the transaction reservation needed to complete an out of place
+ * atomic write of a given number of blocks.
+ */
+int
+xfs_calc_atomic_write_reservation(
+	struct xfs_mount	*mp,
+	xfs_extlen_t		blockcount)
+{
+	unsigned int		new_logres;
+	xfs_extlen_t		min_logblocks;
+
+	/*
+	 * If the caller doesn't ask for a specific atomic write size, then
+	 * use the defaults.
+	 */
+	if (blockcount == 0) {
+		xfs_calc_default_atomic_ioend_reservation(mp, M_RES(mp));
+		return 0;
+	}
+
+	min_logblocks = xfs_calc_atomic_write_log_geometry(mp, blockcount,
+			&new_logres);
+	if (!min_logblocks || min_logblocks > mp->m_sb.sb_logblocks)
+		return -EINVAL;
+
+	M_RES(mp)->tr_atomic_ioend.tr_logres = new_logres;
+	return 0;
+}
diff --git a/fs/xfs/libxfs/xfs_trans_resv.h b/fs/xfs/libxfs/xfs_trans_resv.h
index a6d303b83688..336279e0fc61 100644
--- a/fs/xfs/libxfs/xfs_trans_resv.h
+++ b/fs/xfs/libxfs/xfs_trans_resv.h
@@ -122,5 +122,9 @@ unsigned int xfs_calc_write_reservation_minlogsize(struct xfs_mount *mp);
 unsigned int xfs_calc_qm_dqalloc_reservation_minlogsize(struct xfs_mount *mp);
 
 xfs_extlen_t xfs_calc_max_atomic_write_fsblocks(struct xfs_mount *mp);
+xfs_extlen_t xfs_calc_atomic_write_log_geometry(struct xfs_mount *mp,
+		xfs_extlen_t blockcount, unsigned int *new_logres);
+int xfs_calc_atomic_write_reservation(struct xfs_mount *mp,
+		xfs_extlen_t blockcount);
 
 #endif	/* __XFS_TRANS_RESV_H__ */