MYSQL 8 writes on ibdata1 only when no queries

I'm facing a strange behavior with MySQL 8 running in docker: it has a constant 7MB/s write to ibdata1 when no queries are being made (monitored with netdata and [filetop-bcc](https://github.com/iovisor/bcc/blob/master/tools/filetop.py)) . As soon as I start inserting some data, the write drops, and resume as soon as I stop the inserting process. I've looked at several other threads about ibdata1, but none seems to give a reasonable explanation of why there's such behavior. Here's a graph of disk usage. You can see at first and at last the constant disk write, and in the middle the small amount of time an application inserting/selecting data was running. SHOW FULL PROCESSLIST lists no on-going transaction SELECT * FROM information_schema.innodb_trx returns an empty result My config:

[mysqld]
max_binlog_size = 1048576
innodb_sort_buffer_size = 20971520
sync_binlog = 0
join_buffer_size = 1G
innodb_buffer_pool_size = 22G
innodb_log_file_size = 3G
innodb_buffer_pool_instances = 23
innodb_flush_method = O_DIRECT
innodb_flush_log_at_trx_commit = 2

Does anyone have a clue about what could be going on ? MySQL is giving me quite a high disk PSI (from 3 to 10%), even if my computer has a nvme SSD. EDIT: Apparently it has to do with InnoDB Buffer Pool Flush Pages Requests, which is around 200 requests/s on idle, and drops to 0 as soon as the process connects to mysql. However, I don't understand what it means