bcachefs: Stash a copy of key being overwritten in btree_insert_entry

We currently need to call bch2_btree_path_peek_slot() multiple times in
the transaction commit path - and some of those need to be updated to
also check the keys from journal replay, too. Let's consolidate this and
stash the key being overwritten in btree_insert_entry.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/btree_iter.c

@@ -1987,6 +1987,7 @@ inline struct bkey_s_c bch2_btree_path_peek_slot(struct btree_path *path, struct
 		if (unlikely(!ck->valid))
 			goto hole;
 
+		*u = ck->k->k;
 		k = bkey_i_to_s_c(ck->k);
 	}
 

fs/bcachefs/btree_types.h

@@ -339,12 +339,20 @@ struct btree_insert_entry {
 	unsigned		flags;
 	u8			bkey_type;
 	enum btree_id		btree_id:8;
-	u8			level;
+	u8			level:4;
 	bool			cached:1;
 	bool			insert_trigger_run:1;
 	bool			overwrite_trigger_run:1;
+	/*
+	 * @old_k may be a key from the journal; @old_btree_u64s always refers
+	 * to the size of the key being overwritten in the btree:
+	 */
+	u8			old_btree_u64s;
 	struct bkey_i		*k;
 	struct btree_path	*path;
+	/* key being overwritten: */
+	struct bkey		old_k;
+	const struct bch_val	*old_v;
 	unsigned long		ip_allocated;
 };
 

fs/bcachefs/btree_update_leaf.c

@@ -653,7 +653,6 @@ static inline int do_bch2_trans_commit(struct btree_trans *trans,
 {
 	struct bch_fs *c = trans->c;
 	struct btree_insert_entry *i;
-	struct bkey_s_c old;
 	int ret, u64s_delta = 0;
 
 	trans_for_each_update(trans, i) {
@@ -671,22 +670,11 @@ static inline int do_bch2_trans_commit(struct btree_trans *trans,
 	}
 
 	trans_for_each_update(trans, i) {
-		struct bkey u;
-
-		/*
-		 * peek_slot() doesn't yet work on iterators that point to
-		 * interior nodes:
-		 */
-		if (i->cached || i->level)
+		if (i->cached)
 			continue;
 
-		old = bch2_btree_path_peek_slot(i->path, &u);
-		ret = bkey_err(old);
-		if (unlikely(ret))
-			return ret;
-
 		u64s_delta += !bkey_deleted(&i->k->k) ? i->k->k.u64s : 0;
-		u64s_delta -= !bkey_deleted(old.k) ? old.k->u64s : 0;
+		u64s_delta -= i->old_btree_u64s;
 
 		if (!same_leaf_as_next(trans, i)) {
 			if (u64s_delta <= 0) {
@@ -1432,11 +1420,19 @@ int __must_check bch2_trans_update_by_path(struct btree_trans *trans, struct btr
 		}
 
 		bch2_path_put(trans, i->path, true);
-		*i = n;
-	} else
+		i->flags	= n.flags;
+		i->cached	= n.cached;
+		i->k		= n.k;
+		i->path		= n.path;
+		i->ip_allocated	= n.ip_allocated;
+	} else {
 		array_insert_item(trans->updates, trans->nr_updates,
 				  i - trans->updates, n);
 
+		i->old_v = bch2_btree_path_peek_slot(path, &i->old_k).v;
+		i->old_btree_u64s = !bkey_deleted(&i->old_k) ? i->old_k.u64s : 0;
+	}
+
 	__btree_path_get(n.path, true);
 	return 0;
 }

fs/bcachefs/buckets.c

@@ -1322,25 +1322,14 @@ void fs_usage_apply_warn(struct btree_trans *trans,
 		should_not_have_added, disk_res_sectors);
 
 	trans_for_each_update(trans, i) {
+		struct bkey_s_c old = { &i->old_k, i->old_v };
+
 		pr_err("while inserting");
 		bch2_bkey_val_to_text(&PBUF(buf), c, bkey_i_to_s_c(i->k));
-		pr_err("%s", buf);
+		pr_err("  %s", buf);
 		pr_err("overlapping with");
-
-		if (!i->cached) {
-			struct bkey u;
-			struct bkey_s_c k = bch2_btree_path_peek_slot(i->path, &u);
-
-			bch2_bkey_val_to_text(&PBUF(buf), c, k);
-			pr_err("%s", buf);
-		} else {
-			struct bkey_cached *ck = (void *) i->path->l[0].b;
-
-			if (ck->valid) {
-				bch2_bkey_val_to_text(&PBUF(buf), c, bkey_i_to_s_c(ck->k));
-				pr_err("%s", buf);
-			}
-		}
+		bch2_bkey_val_to_text(&PBUF(buf), c, old);
+		pr_err("  %s", buf);
 	}
 	__WARN();
 }