Index: sys/kern/subr_blist.c
===================================================================
--- sys/kern/subr_blist.c
+++ sys/kern/subr_blist.c
@@ -170,6 +170,28 @@
 }
 
 /*
+ * Use a de Bruijn sequence to find the 1 bit in a daddr_t.
+ * Assumes that the argument has only one bit set.  ffs(x)
+ * could be implemented as return (x==0? 0: 1+bitpos(x&-x)).
+ */
+static inline int
+bitpos(daddr_t mask)
+{
+	const u_daddr_t magic = 0x025f9a9c5643dba3;
+	const unsigned char magictable[64] = {
+		 0,  1,  2, 42,  3, 30, 59, 43,
+		39,  4, 31,  7, 60, 17, 25, 44,
+		40, 57,  5, 23, 21, 32, 34,  8,
+		61, 36, 18, 50, 26, 53, 45, 10,
+		63, 41, 29, 58, 38,  6, 16, 24,
+		56, 22, 20, 33, 35, 49, 52,  9,
+		62, 28, 37, 15, 55, 19, 48, 51,
+		27, 14, 54, 47, 13, 46, 12, 11,
+	};
+	return (magictable[(mask * magic) >> 58]);
+}
+
+/*
  * blist_create() - create a blist capable of handling up to the specified
  *		    number of blocks
  *
@@ -353,13 +375,13 @@
  *
  *	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) + log2(BLIST_BMAP_RADIX).
+ *	time is proportional to log2(count).
  */
 static daddr_t
 blst_leaf_alloc(blmeta_t *scan, daddr_t blk, int count, daddr_t cursor)
 {
 	u_daddr_t mask;
-	int count1, hi, lo, mid, num_shifts, range1, range_ext;
+	int count1, lo, num_shifts, range1, range_ext;
 
 	if (count == BLIST_BMAP_RADIX) {
 		/*
@@ -417,17 +439,10 @@
 	/*
 	 * The least significant set bit in mask marks the start of the first
 	 * available range of sufficient size.  Clear all the bits but that one,
-	 * and then perform a binary search to find its position.
+	 * and find its position.
 	 */
 	mask &= -mask;
-	hi = BLIST_BMAP_RADIX - count1;
-	while (lo + 1 < hi) {
-		mid = (lo + hi) >> 1;
-		if ((mask >> mid) != 0)
-			lo = mid;
-		else
-			hi = mid;
-	}
+	lo = bitpos(mask);
 
 	/*
 	 * Set in mask exactly the bits being allocated, and clear them from