bcachefs: Btree splits now only take the locks they need

Previously, bch2_btree_update_start() would always take all intent
locks, all the way up to the root.

We've finally got data from users where this became a scalability issue
- so, this patch fixes bch2_btree_update_start() to only take the locks
we need.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/btree_update_interior.c b/fs/bcachefs/btree_update_interior.c
index 7619890d9df13accee1b944af139966057721964..84a1cd0a0a4fb808b25573ad61ff58a3412126aa 100644 (file)
--- a/fs/bcachefs/btree_update_interior.c
+++ b/fs/bcachefs/btree_update_interior.c
@@ -1070,23 +1070,23 @@ bch2_btree_update_start(struct btree_trans *trans, struct btree_path *path,
                nr_nodes[!!update_level] += 1 + split;
                update_level++;
 
-               if (!btree_path_node(path, update_level))
-                       break;
+               ret = bch2_btree_path_upgrade(trans, path, update_level + 1);
+               if (ret)
+                       return ERR_PTR(ret);
 
-               /*
-                * XXX: figure out how far we might need to split,
-                * instead of locking/reserving all the way to the root:
-                */
-               split = update_level + 1 < BTREE_MAX_DEPTH;
-       }
+               if (!btree_path_node(path, update_level)) {
+                       /* Allocating new root? */
+                       nr_nodes[1] += split;
+                       update_level = BTREE_MAX_DEPTH;
+                       break;
+               }
 
-       /* Might have to allocate a new root: */
-       if (update_level < BTREE_MAX_DEPTH)
-               nr_nodes[1] += 1;
+               if (bch2_btree_node_insert_fits(c, path->l[update_level].b,
+                                       BKEY_BTREE_PTR_U64s_MAX * (1 + split)))
+                       break;
 
-       ret = bch2_btree_path_upgrade(trans, path, U8_MAX);
-       if (ret)
-               return ERR_PTR(ret);
+               split = true;
+       }
 
        if (flags & BTREE_INSERT_GC_LOCK_HELD)
                lockdep_assert_held(&c->gc_lock);
@@ -1108,6 +1108,7 @@ bch2_btree_update_start(struct btree_trans *trans, struct btree_path *path,
        as->mode        = BTREE_INTERIOR_NO_UPDATE;
        as->took_gc_lock = !(flags & BTREE_INSERT_GC_LOCK_HELD);
        as->btree_id    = path->btree_id;
+       as->update_level = update_level;
        INIT_LIST_HEAD(&as->list);
        INIT_LIST_HEAD(&as->unwritten_list);
        INIT_LIST_HEAD(&as->write_blocked_list);
@@ -1511,7 +1512,7 @@ static int btree_split(struct btree_update *as, struct btree_trans *trans,
        int ret = 0;
 
        BUG_ON(!parent && (b != btree_node_root(c, b)));
-       BUG_ON(!btree_node_intent_locked(path, btree_node_root(c, b)->c.level));
+       BUG_ON(parent && !btree_node_intent_locked(path, b->c.level + 1));
 
        bch2_btree_interior_update_will_free_node(as, b);
 
@@ -1698,7 +1699,7 @@ static int bch2_btree_insert_node(struct btree_update *as, struct btree_trans *t
        int ret;
 
        lockdep_assert_held(&c->gc_lock);
-       BUG_ON(!btree_node_intent_locked(path, btree_node_root(c, b)->c.level));
+       BUG_ON(!btree_node_intent_locked(path, b->c.level));
        BUG_ON(!b->c.level);
        BUG_ON(!as || as->b);
        bch2_verify_keylist_sorted(keys);
@@ -1738,6 +1739,13 @@ static int bch2_btree_insert_node(struct btree_update *as, struct btree_trans *t
        btree_node_interior_verify(c, b);
        return 0;
 split:
+       /*
+        * We could attempt to avoid the transaction restart, by calling
+        * bch2_btree_path_upgrade() and allocating more nodes:
+        */
+       if (b->c.level >= as->update_level)
+               return btree_trans_restart(trans, BCH_ERR_transaction_restart_split_race);
+
        return btree_split(as, trans, path, b, keys, flags);
 }
 
@@ -1763,7 +1771,7 @@ int bch2_btree_split_leaf(struct btree_trans *trans,
 
        bch2_btree_update_done(as, trans);
 
-       for (l = path->level + 1; btree_path_node(path, l) && !ret; l++)
+       for (l = path->level + 1; btree_node_intent_locked(path, l) && !ret; l++)
                ret = bch2_foreground_maybe_merge(trans, path, l, flags);
 
        return ret;

diff --git a/fs/bcachefs/btree_update_interior.h b/fs/bcachefs/btree_update_interior.h
index 7af810df8348e0ae9107ec737ef55f15acea80f1..dabe815965445484d2a24c7ab801d7bf0e19049a 100644 (file)
--- a/fs/bcachefs/btree_update_interior.h
+++ b/fs/bcachefs/btree_update_interior.h
@@ -52,6 +52,7 @@ struct btree_update {
        unsigned                        took_gc_lock:1;
 
        enum btree_id                   btree_id;
+       unsigned                        update_level;
 
        struct disk_reservation         disk_res;
        struct journal_preres           journal_preres;