bcachefs: Kill bpos_diff()

This improves the btree iterator lookup code by using
trans_for_each_iter_inorder().

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

2 files changed, 17 insertions, 47 deletions

diff --git a/fs/bcachefs/bkey.h b/fs/bcachefs/bkey.h
index 2e45d88fab03..c4a66f28ef4b 100644
--- a/fs/bcachefs/bkey.h
+++ b/fs/bcachefs/bkey.h
@@ -163,37 +163,6 @@ static inline struct bpos bpos_max(struct bpos l, struct bpos r)
 	return bpos_cmp(l, r) > 0 ? l : r;
 }
 
-#define sbb(a, b, borrow)				\
-do {							\
-	typeof(a) d1, d2;				\
-							\
-	d1 = a - borrow;				\
-	borrow  = d1 > a;				\
-							\
-	d2 = d1 - b;					\
-	borrow += d2 > d1;				\
-	a = d2;						\
-} while (0)
-
-/* returns a - b: */
-static inline struct bpos bpos_sub(struct bpos a, struct bpos b)
-{
-	int borrow = 0;
-
-	sbb(a.snapshot, b.snapshot,	borrow);
-	sbb(a.offset,	b.offset,	borrow);
-	sbb(a.inode,	b.inode,	borrow);
-	return a;
-}
-
-static inline struct bpos bpos_diff(struct bpos l, struct bpos r)
-{
-	if (bpos_cmp(l, r) > 0)
-		swap(l, r);
-
-	return bpos_sub(r, l);
-}
-
 void bch2_bpos_swab(struct bpos *);
 void bch2_bkey_swab_key(const struct bkey_format *, struct bkey_packed *);
 
diff --git a/fs/bcachefs/btree_iter.c b/fs/bcachefs/btree_iter.c
index 9ba0dc402d89..cdd6f6c81fb2 100644
--- a/fs/bcachefs/btree_iter.c
+++ b/fs/bcachefs/btree_iter.c
@@ -2299,8 +2299,9 @@ struct btree_iter *__bch2_trans_get_iter(struct btree_trans *trans,
 					 unsigned depth,
 					 unsigned flags)
 {
-	struct btree_iter *iter, *best = NULL;
+	struct btree_iter *iter, *list_pos = NULL, *best = NULL;
 	struct bpos real_pos, pos_min = POS_MIN;
+	int cmp;
 
 	EBUG_ON(trans->restarted);
 
@@ -2324,27 +2325,27 @@ struct btree_iter *__bch2_trans_get_iter(struct btree_trans *trans,
 	    bkey_cmp(pos, POS_MAX))
 		real_pos = bpos_nosnap_successor(pos);
 
-	trans_for_each_iter(trans, iter) {
-		if (btree_iter_type(iter) != (flags & BTREE_ITER_TYPE))
-			continue;
+	trans_for_each_iter_inorder(trans, iter) {
+		list_pos = iter;
 
-		if (iter->btree_id != btree_id)
+		if (btree_iter_type(iter) != (flags & BTREE_ITER_TYPE) ||
+		    iter->btree_id	!= btree_id)
 			continue;
 
-		if (best) {
-			int cmp = bkey_cmp(bpos_diff(best->real_pos, real_pos),
-					   bpos_diff(iter->real_pos, real_pos));
-
-			if (cmp < 0 ||
-			    ((cmp == 0 && btree_iter_keep(trans, iter))))
-				continue;
-		}
-
-		best = iter;
+		/*
+		 * Since advancing iterators is cheaper than rewinding them, we
+		 * prefer a path <= the search pos
+		 */
+		cmp   = bpos_cmp(iter->real_pos, real_pos) ?:
+			cmp_int(iter->level, depth);
+		if (!best || cmp <= 0)
+			best = iter;
+		if (cmp >= 0)
+			break;
 	}
 
 	if (!best) {
-		iter = btree_trans_iter_alloc(trans, NULL);
+		iter = btree_trans_iter_alloc(trans, list_pos);
 		bch2_btree_iter_init(trans, iter, btree_id);
 	} else if (btree_iter_keep(trans, best)) {
 		iter = btree_trans_iter_alloc(trans, best);