bcachefs: Kill btree_iter->journal_pos

For BTREE_ITER_WITH_JOURNAL, we memoize lookups in the journal keys, to
avoid the binary search overhead.

Previously we stashed the pos of the last key returned from the journal,
in order to force the lookup to be redone when rewinding.

Now bch2_journal_keys_peek_upto() handles rewinding itself when
necessary - so we can slim down btree_iter.

Signed-off-by: Kent Overstreet <[e-mail]>

fs/bcachefs/btree_iter.c

···
 					      struct btree_iter *iter,
 					      struct bpos end_pos)
 {
-	struct bkey_i *k;
-
-	if (bpos_lt(iter->path->pos, iter->journal_pos))
-		iter->journal_idx = 0;
-
-	k = bch2_journal_keys_peek_upto(trans->c, iter->btree_id,
-					iter->path->level,
-					iter->path->pos,
-					end_pos,
-					&iter->journal_idx);
-
-	iter->journal_pos = k ? k->k.p : end_pos;
-	return k;
+	return bch2_journal_keys_peek_upto(trans->c, iter->btree_id,
+					   iter->path->level,
+					   iter->path->pos,
+					   end_pos,
+					   &iter->journal_idx);
 }
 
 static noinline

fs/bcachefs/btree_iter.h

···
 	iter->pos		= pos;
 	iter->k			= POS_KEY(pos);
 	iter->journal_idx	= 0;
-	iter->journal_pos	= POS_MIN;
 #ifdef CONFIG_BCACHEFS_DEBUG
 	iter->ip_allocated = ip;
 #endif

fs/bcachefs/btree_journal_iter.c

···
 	return idx_to_pos(keys, __bch2_journal_key_search(keys, id, level, pos));
 }
 
+/* Returns first non-overwritten key >= search key: */
 struct bkey_i *bch2_journal_keys_peek_upto(struct bch_fs *c, enum btree_id btree_id,
 					   unsigned level, struct bpos pos,
 					   struct bpos end_pos, size_t *idx)
···
 	if (!*idx)
 		*idx = __bch2_journal_key_search(keys, btree_id, level, pos);
 
+	while (*idx &&
+	       __journal_key_cmp(btree_id, level, end_pos, idx_to_key(keys, *idx - 1)) <= 0) {
+		--(*idx);
+		iters++;
+		if (iters == 10) {
+			*idx = 0;
+			goto search;
+		}
+	}
+
 	while ((k = *idx < keys->nr ? idx_to_key(keys, *idx) : NULL)) {
 		if (__journal_key_cmp(btree_id, level, end_pos, k) < 0)
 			return NULL;
 
-		if (__journal_key_cmp(btree_id, level, pos, k) <= 0 &&
-		    !k->overwritten)
+		if (k->overwritten) {
+			(*idx)++;
+			continue;
+		}
+
+		if (__journal_key_cmp(btree_id, level, pos, k) <= 0)
 			return k->k;
 
 		(*idx)++;

fs/bcachefs/btree_types.h

···
 
 	/* BTREE_ITER_WITH_JOURNAL: */
 	size_t			journal_idx;
-	struct bpos		journal_pos;
 #ifdef TRACK_PATH_ALLOCATED
 	unsigned long		ip_allocated;
 #endif