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Diffstat (limited to 'fs/xfs/libxfs/xfs_alloc.c')
-rw-r--r--fs/xfs/libxfs/xfs_alloc.c27
1 files changed, 24 insertions, 3 deletions
diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
index 3069194527dd..100ab5931b31 100644
--- a/fs/xfs/libxfs/xfs_alloc.c
+++ b/fs/xfs/libxfs/xfs_alloc.c
@@ -2275,16 +2275,37 @@ xfs_alloc_min_freelist(
ASSERT(mp->m_alloc_maxlevels > 0);
+ /*
+ * For a btree shorter than the maximum height, the worst case is that
+ * every level gets split and a new level is added, then while inserting
+ * another entry to refill the AGFL, every level under the old root gets
+ * split again. This is:
+ *
+ * (full height split reservation) + (AGFL refill split height)
+ * = (current height + 1) + (current height - 1)
+ * = (new height) + (new height - 2)
+ * = 2 * new height - 2
+ *
+ * For a btree of maximum height, the worst case is that every level
+ * under the root gets split, then while inserting another entry to
+ * refill the AGFL, every level under the root gets split again. This is
+ * also:
+ *
+ * 2 * (current height - 1)
+ * = 2 * (new height - 1)
+ * = 2 * new height - 2
+ */
+
/* space needed by-bno freespace btree */
min_free = min_t(unsigned int, levels[XFS_BTNUM_BNOi] + 1,
- mp->m_alloc_maxlevels);
+ mp->m_alloc_maxlevels) * 2 - 2;
/* space needed by-size freespace btree */
min_free += min_t(unsigned int, levels[XFS_BTNUM_CNTi] + 1,
- mp->m_alloc_maxlevels);
+ mp->m_alloc_maxlevels) * 2 - 2;
/* space needed reverse mapping used space btree */
if (xfs_has_rmapbt(mp))
min_free += min_t(unsigned int, levels[XFS_BTNUM_RMAPi] + 1,
- mp->m_rmap_maxlevels);
+ mp->m_rmap_maxlevels) * 2 - 2;
return min_free;
}