svn commit: r347462 - head/sys/kern

[Doug Moore]

Author: dougm
Date: Fri May 10 18:25:06 2019
New Revision: 347462
URL: https://svnweb.freebsd.org/changeset/base/347462

Log:
  blist_next_leaf_alloc walks over all the meta-nodes between one leaf
  and the next one, and if blocks are allocated from the next leaf, it
  walks back toward where it started, as long as there are interleaving
  meta-nodes to be updated on account of the last free blocks under
  those meta-nodes being allocated. Only if the walk goes all the way
  back to the starting point must we calculate the position of the
  meta-node that is the least-comment parent of one leaf and the next,
  and update a bit in that meta-node to indicate the allocation of its
  last free block.
  
  There's no need to start calculating the position of that least-common
  parent until the walk back reaches the original starting point, and
  there's no need for a calculation that updates 'radius' to tell us
  when we've walked back to the beginning, since comparing scan to next
  suffices for that.
  
  Approved by: kib (mentor)
  Differential Revision: https://reviews.freebsd.org/D20229

Modified:
  head/sys/kern/subr_blist.c

Modified: head/sys/kern/subr_blist.c
==============================================================================
--- head/sys/kern/subr_blist.c	Fri May 10 18:22:40 2019	(r347461)
+++ head/sys/kern/subr_blist.c	Fri May 10 18:25:06 2019	(r347462)
@@ -607,7 +607,6 @@ static int
 blst_next_leaf_alloc(blmeta_t *scan, daddr_t blk, int count)
 {
 	blmeta_t *next;
-	daddr_t skip;
 	u_daddr_t radix;
 	int digit;
 
@@ -632,13 +631,14 @@ blst_next_leaf_alloc(blmeta_t *scan, daddr_t blk, int 
 	/*
 	 * Update bitmaps of next-ancestors, up to least common ancestor.
 	 */
-	skip = radix_to_skip(radix);
-	while (radix != BLIST_BMAP_RADIX && next->bm_bitmap == 0) {
-		(--next)->bm_bitmap ^= 1;
-		radix /= BLIST_META_RADIX;
-	}
-	if (next->bm_bitmap == 0)
-		scan[-digit * skip].bm_bitmap ^= (u_daddr_t)1 << digit;
+	while (next->bm_bitmap == 0) {
+		if (--next == scan) {
+			scan[-digit * radix_to_skip(radix)].bm_bitmap ^=
+			    (u_daddr_t)1 << digit;
+			break;
+		}
+		next->bm_bitmap ^= 1;
+ 	}
 	return (0);
 }