I noticed the same behavior, but I just have to wait 15 minutes
Looking at the logs, it seems that samba is accessing all shared files, maybe an ACL check? I see lots and lots of "smbd_audit" line from 127.0.0.1.
During a configuration change, samba module restart or reboot, these 2 samba processes hogs the cpu:
/opt/samba4/sbin/smbd -D --option=server role check:inhibit=yes --foreground
/opt/samba4/sbin/smbd -D
Also iotop only shows "disk write" and no "disk read" from:
/opt/samba4/sbin/smbd -D --option=server role check:inhibit=yes --foreground
I tried to find documentation about the "server role check:inhibit=yes" parameter, but searching the man pages and google gives no usefull result ...
I did not dig any deeper, maybe a strace of the samba process will show what is happening. Or someone with more samba4 knowledge will let us know