[PATCH v2 2/3] xfs: support additional levels in the agfl minimum calculation

[Brian Foster <bfoster@redhat.com>]

xfs_alloc_min_freelist() calculates the worst case AGFL block
requirement for a full split plus partial refill for each alloc
btree. An upcoming patch needs to calculate the requirement for
multiple level increases, so add an optional extra levels parameter
and factor out a wrapper function for the common case of a single
split. No functional changes.

Assisted-by: LLM
Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/xfs/libxfs/xfs_alloc.c | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
index d99602bcc16f..dbb85fb6314b 100644
--- a/fs/xfs/libxfs/xfs_alloc.c
+++ b/fs/xfs/libxfs/xfs_alloc.c
@@ -2439,17 +2439,22 @@ xfs_alloc_longest_free_extent(
 
 /*
  * Compute the minimum length of the AGFL in the given AG.  If @pag is NULL,
- * return the largest possible minimum length.
+ * return the largest possible minimum length. The base calculation accounts
+ * for a single full split per btree. @extra_levels adds additional split
+ * levels to compute the prospective AGFL requirement increase for
+ * multi-allocation transactions.
  */
-unsigned int
-xfs_alloc_min_freelist(
+static unsigned int
+__xfs_alloc_min_freelist(
 	struct xfs_mount	*mp,
-	struct xfs_perag	*pag)
+	struct xfs_perag	*pag,
+	unsigned int		extra_levels)
 {
 	/* AG btrees have at least 1 level. */
 	const unsigned int	bno_level = pag ? pag->pagf_bno_level : 1;
 	const unsigned int	cnt_level = pag ? pag->pagf_cnt_level : 1;
 	const unsigned int	rmap_level = pag ? pag->pagf_rmap_level : 1;
+	const unsigned int	levels = 1 + extra_levels;
 	unsigned int		min_free;
 
 	ASSERT(mp->m_alloc_maxlevels > 0);
@@ -2476,15 +2481,25 @@ xfs_alloc_min_freelist(
 	 */
 
 	/* space needed by-bno freespace btree */
-	min_free = min(bno_level + 1, mp->m_alloc_maxlevels) * 2 - 2;
+	min_free = min(bno_level + levels, mp->m_alloc_maxlevels) * 2 - 2;
 	/* space needed by-size freespace btree */
-	min_free += min(cnt_level + 1, mp->m_alloc_maxlevels) * 2 - 2;
+	min_free += min(cnt_level + levels, mp->m_alloc_maxlevels) * 2 - 2;
 	/* space needed reverse mapping used space btree */
-	if (xfs_has_rmapbt(mp))
-		min_free += min(rmap_level + 1, mp->m_rmap_maxlevels) * 2 - 2;
+	if (xfs_has_rmapbt(mp)) {
+		min_free += min(rmap_level + levels,
+				mp->m_rmap_maxlevels) * 2 - 2;
+	}
 	return min_free;
 }
 
+unsigned int
+xfs_alloc_min_freelist(
+	struct xfs_mount	*mp,
+	struct xfs_perag	*pag)
+{
+	return __xfs_alloc_min_freelist(mp, pag, 0);
+}
+
 /*
  * Check if the operation we are fixing up the freelist for should go ahead or
  * not. If we are freeing blocks, we always allow it, otherwise the allocation
-- 
2.55.0