/dev/shm not used?

[ZeDoudou]

Hello,

I installed one monitor in a container installed on a Debian.
It is working but events are a bit laggy and I see lots of disk access (disk light on computer case).
I made lots of search on Google but did not solve this issue...

/dev/shm seems to be well initiated but it's only use 43Mo of 4Go :

root@gladiatux:~# docker exec zoneminder ls -l /dev/shm
total 43208
-rw-rw---- 1 www-data www-data 44242360 May 16 23:55 zm.mmap.1

root@gladiatux:~# docker exec zoneminder df -h
Filesystem                              Size  Used Avail Use% Mounted on
overlay                                  50G   40G  7.2G  85% /
tmpfs                                    64M     0   64M   0% /dev
shm                                     4.0G   43M  4.0G   2% /dev/shm
...

zm.mmap.1 does not change after docker creation.

Do you have any idea where it could from?
Thanks in advance, best regards.