bcachefs: kill bset_tree->max_key

Since we now ensure a btree node's max key fits in its packed format,
this isn't needed for the reasons it used to be - and, it was being used
inconsistently.

Also reorder struct btree a bit for performance, and kill some dead
code.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/bset.c

@@ -686,7 +686,7 @@ static void make_bfloat(struct btree *b, struct bset_tree *t,
 		if (!bkey_pack_pos(max_key, b->data->max_key, b)) {
 			k = (void *) max_key;
 			bkey_init(&k->k);
-			k->k.p = t->max_key;
+			k->k.p = b->data->max_key;
 		}
 	}
 
@@ -770,8 +770,6 @@ static noinline void __build_ro_aux_tree(struct btree *b, struct bset_tree *t)
 	while (k != btree_bkey_last(b, t))
 		prev = k, k = bkey_next(k);
 
-	t->max_key = bkey_unpack_pos(b, prev);
-
 	if (!bkey_pack_pos(bkey_to_packed(&min_key), b->data->min_key, b)) {
 		bkey_init(&min_key.k);
 		min_key.k.p = b->data->min_key;
@@ -779,7 +777,7 @@ static noinline void __build_ro_aux_tree(struct btree *b, struct bset_tree *t)
 
 	if (!bkey_pack_pos(bkey_to_packed(&max_key), b->data->max_key, b)) {
 		bkey_init(&max_key.k);
-		max_key.k.p = t->max_key;
+		max_key.k.p = b->data->max_key;
 	}
 
 	/* Then we build the tree */
@@ -958,8 +956,6 @@ static void ro_aux_tree_fix_invalidated_key(struct btree *b,
 	min_key.u64s = max_key.u64s = 0;
 
 	if (bkey_next(k) == btree_bkey_last(b, t)) {
-		t->max_key = bkey_unpack_pos(b, k);
-
 		for (j = 1; j < t->size; j = j * 2 + 1)
 			make_bfloat(b, t, j, &min_key, &max_key);
 	}
@@ -1299,16 +1295,6 @@ struct bkey_packed *__bch2_bset_search(struct btree *b,
 	case BSET_RW_AUX_TREE:
 		return bset_search_write_set(b, t, search);
 	case BSET_RO_AUX_TREE:
-		/*
-		 * Each node in the auxiliary search tree covers a certain range
-		 * of bits, and keys above and below the set it covers might
-		 * differ outside those bits - so we have to special case the
-		 * start and end - handle that here:
-		 */
-
-		if (bpos_cmp(*search, t->max_key) > 0)
-			return btree_bkey_last(b, t);
-
 		return bset_search_tree(b, t, search, lossy_packed_search);
 	default:
 		unreachable();
@@ -1345,23 +1331,6 @@ struct bkey_packed *bch2_bset_search_linear(struct btree *b,
 	return m;
 }
 
-/*
- * Returns the first key greater than or equal to @search
- */
-static __always_inline __flatten
-struct bkey_packed *bch2_bset_search(struct btree *b,
-				struct bset_tree *t,
-				struct bpos *search,
-				struct bkey_packed *packed_search,
-				const struct bkey_packed *lossy_packed_search)
-{
-	struct bkey_packed *m = __bch2_bset_search(b, t, search,
-						   lossy_packed_search);
-
-	return bch2_bset_search_linear(b, t, search,
-				 packed_search, lossy_packed_search, m);
-}
-
 /* Btree node iterator */
 
 static inline void __bch2_btree_node_iter_push(struct btree_node_iter *iter,
@@ -1457,6 +1426,7 @@ void bch2_btree_node_iter_init(struct btree_node_iter *iter,
 	unsigned i;
 
 	EBUG_ON(bpos_cmp(*search, b->data->min_key) < 0);
+	EBUG_ON(bpos_cmp(*search, b->data->max_key) > 0);
 	bset_aux_tree_verify(b);
 
 	memset(iter, 0, sizeof(*iter));

fs/bcachefs/btree_types.h

@@ -47,8 +47,6 @@ struct bset_tree {
 	u16			data_offset;
 	u16			aux_data_offset;
 	u16			end_offset;
-
-	struct bpos		max_key;
 };
 
 struct btree_write {
@@ -98,6 +96,11 @@ struct btree {
 	u8			byte_order;
 	u8			unpack_fn_len;
 
+	struct btree_write	writes[2];
+
+	/* Key/pointer for this btree node */
+	__BKEY_PADDED(key, BKEY_BTREE_PTR_VAL_U64s_MAX);
+
 	/*
 	 * XXX: add a delete sequence number, so when bch2_btree_node_relock()
 	 * fails because the lock sequence number has changed - i.e. the
@@ -128,11 +131,6 @@ struct btree {
 
 	/* lru list */
 	struct list_head	list;
-
-	struct btree_write	writes[2];
-
-	/* Key/pointer for this btree node */
-	__BKEY_PADDED(key, BKEY_BTREE_PTR_VAL_U64s_MAX);
 };
 
 struct btree_cache {