On Wed, Oct 13, 2021 at 04:49:39PM +1100, Dave Chinner wrote:

On Tue, Oct 12, 2021 at 04:33:28PM -0700, Darrick J. Wong wrote:

quoted

From: Darrick J. Wong <djwong@kernel.org>

Compute the actual maximum btree height when deciding if per-AG block
reservation is critically low.  This only affects the sanity check
condition, since we /generally/ will trigger on the 10% threshold.
This is a long-winded way of saying that we're removing one more
usage of XFS_BTREE_MAXLEVELS.

And replacing it with a branchy dynamic calculation that has a
static, unchanging result. :(

quoted

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
 fs/xfs/libxfs/xfs_ag_resv.c |   18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/libxfs/xfs_ag_resv.c b/fs/xfs/libxfs/xfs_ag_resv.c
index 2aa2b3484c28..d34d4614f175 100644
--- a/fs/xfs/libxfs/xfs_ag_resv.c
+++ b/fs/xfs/libxfs/xfs_ag_resv.c

@@ -60,6 +60,20 @@
  * to use the reservation system should update ask/used in xfs_ag_resv_init.
  */
 
+/* Compute maximum possible height for per-AG btree types for this fs. */
+static unsigned int
+xfs_ag_btree_maxlevels(
+	struct xfs_mount	*mp)
+{
+	unsigned int		ret = mp->m_ag_maxlevels;
+
+	ret = max(ret, mp->m_bm_maxlevels[XFS_DATA_FORK]);
+	ret = max(ret, mp->m_bm_maxlevels[XFS_ATTR_FORK]);
+	ret = max(ret, M_IGEO(mp)->inobt_maxlevels);
+	ret = max(ret, mp->m_rmap_maxlevels);
+	return max(ret, mp->m_refc_maxlevels);
+}

Hmmmm. perhaps mp->m_ag_maxlevels should be renamed to
mp->m_agbno_maxlevels and we pre-calculate mp->m_ag_maxlevels from

I prefer m_alloc_maxlevels for the first one, since "agbno" means "AG
block number" in my head.

As for the second, how about "m_agbtree_maxlevels" since we already use
'agbtree' to refer to per-AG btrees elsewhere?

Other than the naming, I agree with your suggestion.

--D

the above function and just use the variable in the
xfs_ag_resv_critical() check?

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com