Index: sys/kern/subr_blist.c
===================================================================
--- sys/kern/subr_blist.c
+++ sys/kern/subr_blist.c
@@ -606,13 +606,17 @@
 blst_next_leaf_alloc(blmeta_t *scan, daddr_t blk, int count)
 {
 	blmeta_t *next;
-	daddr_t skip;
 	u_daddr_t radix;
 	int digit;
 
 	next = scan + 1;
 	blk += BLIST_BMAP_RADIX;
 	radix = BLIST_BMAP_RADIX;
+
+	/*
+	 * Skip meta-nodes, and find the position of the next leaf and their
+	 * least common ancestor.
+	 */
 	while ((digit = ((blk / radix) & BLIST_META_MASK)) == 0 &&
 	    (next->bm_bitmap & 1) == 1) {
 		next++;
@@ -629,15 +633,21 @@
 	next->bm_bitmap &= (u_daddr_t)-1 << count;
 
 	/*
-	 * Update bitmaps of next-ancestors, up to least common ancestor.
+	 * Update meta-node bitmaps of next-ancestors, up to the least common
+	 * ancestor of scan and next.
 	 */
-	skip = radix_to_skip(radix);
-	while (radix != BLIST_BMAP_RADIX && next->bm_bitmap == 0) {
-		(--next)->bm_bitmap ^= 1;
-		radix /= BLIST_META_RADIX;
+	while (next->bm_bitmap == 0) {
+		if (--next == scan) {
+			/*
+			 * In their least common ancestor, mark the node
+			 * containing next as full.
+			 */
+			next[-digit * radix_to_skip(radix)].bm_bitmap ^=
+			    (u_daddr_t)1 << digit;
+			break;
+		}
+		next->bm_bitmap ^= 1;
 	}
-	if (next->bm_bitmap == 0)
-		scan[-digit * skip].bm_bitmap ^= (u_daddr_t)1 << digit;
 	return (0);
 }
 
Index: sys/sys/blist.h
===================================================================
--- sys/sys/blist.h
+++ sys/sys/blist.h
@@ -69,11 +69,11 @@
 #define SWAPBLK_NONE	((daddr_t)((u_daddr_t)SWAPBLK_MASK + 1))/* flag */
 
 /*
- * Both blmeta and bmu_bitmap MUST be a power of 2 in size.
+ * Both blmeta and bm_bitmap MUST be a power of 2 in size.
  */
 
 typedef struct blmeta {
-	u_daddr_t	bm_bitmap;	/* bitmap if we are a leaf	*/
+	u_daddr_t	bm_bitmap;	/* bitmap marking unfilled block sets*/
 	daddr_t		bm_bighint;	/* biggest contiguous block hint*/
 } blmeta_t;