bcachefs: Kill equiv_seen arg to delete_dead_snapshots_process_key()

When deleting dead snapshots, we move keys from redundant interior
snapshot nodes to child nodes - unless there's already a key, in which
case the ancestor key is deleted.

Previously, we tracked via equiv_seen whether the child snapshot had a
key, but this was tricky w.r.t. transaction restarts, and not
transactionally safe w.r.t. updates in the child snapshot.

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

diff --git a/fs/bcachefs/snapshot.c b/fs/bcachefs/snapshot.c
index ac664888847f81494ab58ff3f1cafa104645f988..ca7e4e975a60bc64235590e629e9720b3f3ba20a 100644 (file)
--- a/fs/bcachefs/snapshot.c
+++ b/fs/bcachefs/snapshot.c
@@ -1421,9 +1421,7 @@ int bch2_snapshot_node_create(struct btree_trans *trans, u32 parent,
 static int delete_dead_snapshots_process_key(struct btree_trans *trans,
                               struct btree_iter *iter,
                               struct bkey_s_c k,
-                              snapshot_id_list *deleted,
-                              snapshot_id_list *equiv_seen,
-                              struct bpos *last_pos)
+                              snapshot_id_list *deleted)
 {
        int ret = bch2_check_key_has_snapshot(trans, iter, k);
        if (ret)
@@ -1434,24 +1432,10 @@ static int delete_dead_snapshots_process_key(struct btree_trans *trans,
        if (!equiv) /* key for invalid snapshot node, but we chose not to delete */
                return 0;
 
-       if (!bkey_eq(k.k->p, *last_pos))
-               equiv_seen->nr = 0;
-
        if (snapshot_list_has_id(deleted, k.k->p.snapshot))
                return bch2_btree_delete_at(trans, iter,
                                            BTREE_UPDATE_internal_snapshot_node);
 
-       if (!bpos_eq(*last_pos, k.k->p) &&
-           snapshot_list_has_id(equiv_seen, equiv))
-               return bch2_btree_delete_at(trans, iter,
-                                           BTREE_UPDATE_internal_snapshot_node);
-
-       *last_pos = k.k->p;
-
-       ret = snapshot_list_add_nodup(c, equiv_seen, equiv);
-       if (ret)
-               return ret;
-
        /*
         * When we have a linear chain of snapshot nodes, we consider
         * those to form an equivalence class: we're going to collapse
@@ -1473,20 +1457,23 @@ static int delete_dead_snapshots_process_key(struct btree_trans *trans,
 
                new->k.p.snapshot = equiv;
 
-               struct btree_iter new_iter;
-               bch2_trans_iter_init(trans, &new_iter, iter->btree_id, new->k.p,
-                                    BTREE_ITER_all_snapshots|
-                                    BTREE_ITER_cached|
-                                    BTREE_ITER_intent);
-
-               ret =   bch2_btree_iter_traverse(&new_iter) ?:
-                       bch2_trans_update(trans, &new_iter, new,
-                                       BTREE_UPDATE_internal_snapshot_node) ?:
-                       bch2_btree_delete_at(trans, iter,
-                                       BTREE_UPDATE_internal_snapshot_node);
-               bch2_trans_iter_exit(trans, &new_iter);
+               struct btree_iter dst_iter;
+               struct bkey_s_c dst_k = bch2_bkey_get_iter(trans, &dst_iter,
+                                                          iter->btree_id, new->k.p,
+                                                          BTREE_ITER_all_snapshots|
+                                                          BTREE_ITER_intent);
+               ret = bkey_err(dst_k);
                if (ret)
                        return ret;
+
+               ret =   (bkey_deleted(dst_k.k)
+                        ? bch2_trans_update(trans, &dst_iter, new,
+                                            BTREE_UPDATE_internal_snapshot_node)
+                        : 0) ?:
+                       bch2_btree_delete_at(trans, iter,
+                                            BTREE_UPDATE_internal_snapshot_node);
+               bch2_trans_iter_exit(trans, &dst_iter);
+               return ret;
        }
 
        return 0;
@@ -1648,8 +1635,6 @@ int bch2_delete_dead_snapshots(struct bch_fs *c)
                goto err;
 
        for (unsigned btree = 0; btree < BTREE_ID_NR; btree++) {
-               struct bpos last_pos = POS_MIN;
-               snapshot_id_list equiv_seen = { 0 };
                struct disk_reservation res = { 0 };
 
                if (!btree_type_has_snapshots(btree))
@@ -1659,11 +1644,9 @@ int bch2_delete_dead_snapshots(struct bch_fs *c)
                                btree, POS_MIN,
                                BTREE_ITER_prefetch|BTREE_ITER_all_snapshots, k,
                                &res, NULL, BCH_TRANS_COMMIT_no_enospc,
-                       delete_dead_snapshots_process_key(trans, &iter, k, &deleted,
-                                                         &equiv_seen, &last_pos));
+                       delete_dead_snapshots_process_key(trans, &iter, k, &deleted));
 
                bch2_disk_reservation_put(c, &res);
-               darray_exit(&equiv_seen);
 
                bch_err_msg(c, ret, "deleting keys from dying snapshots");
                if (ret)