Index: sys/kern/subr_blist.c
===================================================================
--- sys/kern/subr_blist.c
+++ sys/kern/subr_blist.c
@@ -644,14 +644,14 @@
 /*
  * BLST_LEAF_ALLOC() -	allocate at a leaf in the radix tree (a bitmap).
  *
- *	This is the core of the allocator and is optimized for the
- *	BLIST_BMAP_RADIX block allocation case.  Otherwise, execution
- *	time is proportional to log2(count) + bitpos time.
+ *	This is the core of the allocator.  Execution time is proportional
+ *	to log(count), plus height of the tree if the allocation crosses a
+ *	leaf boundary.
  */
 static daddr_t
 blst_leaf_alloc(blmeta_t *scan, daddr_t blk, int count)
 {
-	u_daddr_t mask;
+	u_daddr_t cursor_mask, mask;
 	int count1, hi, lo, num_shifts, range1, range_ext;
 
 	range1 = 0;
@@ -691,9 +691,22 @@
 	}
 
 	/* Discard any candidates that appear before blk. */
-	mask &= (u_daddr_t)-1 << (blk & BLIST_BMAP_MASK);
-	if (mask == 0)
-		return (SWAPBLK_NONE);
+	if ((blk & BLIST_BMAP_MASK) != 0) {
+		cursor_mask = mask & bitrange(0, blk & BLIST_BMAP_MASK);
+		if (cursor_mask != 0) {
+			mask ^= cursor_mask;
+			if (mask == 0)
+				return (SWAPBLK_NONE);
+
+			/*
+			 * Bighint change for last block allocation cannot
+			 * assume that any other block are allocated, so the
+			 * bighint cannot be reduced much.
+			 */
+			range1 = BLIST_MAX_ALLOC - 1;
+		}
+		blk &= ~BLIST_BMAP_MASK;
+	}
 
 	/*
 	 * The least significant set bit in mask marks the start of the first
@@ -734,7 +747,7 @@
 	}
 	/* Clear the allocated bits from this leaf. */
 	scan->bm_bitmap &= ~mask;
-	return ((blk & ~BLIST_BMAP_MASK) + lo);
+	return (blk + lo);
 }
 
 /*