QFS filesystem "mm" device inode usage and recovery

Question

I have questions regarding inode usage on a QFS filesystem. Our QFS filesystem “mm” devices are filling up rather quickly and we are trying to understand why. The SAMFS/QFS documentation doesn’t go into that much detail on explaining inode usage from a metadevice standpoint. Here is a small part of the output from “samcmd –m” command:
mm 1001 95% on 0 3.996G 206.875M [423680 inodes]
mm 1001 100% on 0 3.996G 0 [0 inodes]
The first question I have: When do the “mm” device inodes get created, or better yet get USED? I understand files and directories are assigned inodes, but we have observed that just creating files and directories doesn’t USE the “mm” inodes. I have created multiple files and directories in our QFS filesystem, ran the “samcmd –m” command, and the output of free inodes is still the same.
Next question: How does the QFS filesystem recover “mm” device inodes? Just removing a couple files doesn’t increase the number of inodes available, but in one instance I deleted 60000 directories and suddenly over 400000 inodes are freed up. Is there a correlation between inodes freed up and the files? I would figure there would be one inode for each, but there seems to be more. I understand samfsck would recover inodes as well.
Basically my goal is to understand when the inodes are created/used up and how they are recovered. I understand that I may need to add additional “mm” devices, using the samgrowfs command, but don’t want to do that quite yet. Any help understanding QFS "mm" device inode usage and recovery is appreciated.

Answer 1

The PC was indeed turned off between the two checks.
However the first check was not performed right before the shutdown, but few hours before it.
:idea:
(...) varying from browser cache data increase to a cronjob like updatedb, or even you installing or downloading something.
When I've read these words I have started to "scroll" back in my memory buffer and eventually I've remembered that the only thing I did as superuser was to download some Firefox extensions which (surprise or not...) summed up to ~12M.
So we have the answer for this one too thanks to your hints
PS: That's exactly the reason why I've made a small / partition - to keep a close eye on it's usage and to ring some allarms when needed.
Again, thank you.