Postgresql – Postgres 12 large objects memory allocation

there’s an aspect of Postgres memory allocation about large data object I don’t understand.

In more details, statistics about memory allocation don’t match with allocation calculated considering involved tables

PostgreSQL version: 12

I have 5 tables using lob fields in my db, implemented as oid and related large objects.

If I execute this query

select pg_database_size ('<db_name>')

dbms tells me that size is 2.8 gb

If I execute this query

SELECT
    table_schema || '.' || table_name AS table_full_name,
    pg_size_pretty(pg_total_relation_size('"' || table_schema || '"."' || table_name || '"')) AS size
FROM information_schema.tables
ORDER BY
    pg_total_relation_size('"' || table_schema || '"."' || table_name || '"') DESC;

dbms tells me that large objects table is 2.6 gb large

Dry running vaccumlo, I can find which tables are using large objects, they are 5

• string_value in al_system_conf
• email_body in als_email_record
• body in als_mail_history
• content in als_resource
• doc_content in pm_document

Considering that large objects are stored in page of 2048 kb, I can estimate memory consumption of each table, that gives me

If I dry run vacuumlo, it says there are not orphans

So, how can I find how the 2.6 gb are allocated?
How can I free them?