Why Do I Always Have 8 GB RAM Free?

[brando56894]

This isn't specifically related to BSD, but I guess all Unix-like OSes. I remembered noticing that FreeNAS would only use a max of 22 GB out of my 32 GB worth of RAM, I remember seeing that the minimum recommended RAM was 8 GB and maybe there was some specific tuning in FreeNAS to make it this way. When I switched to Linux, I still have those same 8 GB free even though I told my ARC to use all available RAM, even after the server has been on for two weeks. Is this something related to ZFS were it automatically allocates 8 GB for it to use no matter what?

According to the ArcStat.sh script I currently have a 14 GB ARC and 22 GB out of my total 32 GB are used, which means 5 GB are used by my VMs and 2 GB are used by various other things.

Code:

 [root@nas bran]# free -m
              total        used        free      shared  buff/cache   available
Mem:          30060       21439        1182           1        7439        7884

 

[m0nkey_]

You don't have 8GB free, you have 1GB. Roughly 8GB is in use by cache which can be freed.

 

[Ericloewe]

Why don't free and buff/cache add up to available? There's a ~700MB difference.

 

[brando56894]

No idea

You don't have 8GB free, you have 1GB. Roughly 8GB is in use by cache which can be freed.

Haha yea it's pretty obvious when I take a look at free, I always use htop and tend to forget about cache.

It looks like dropping my cache also cleared out most of my ARC, which makes sense I guess since it is a cache after all.

Code:

[root@nas ~]# sync; echo 3 > /proc/sys/vm/drop_caches
[root@nas ~]# free -m
              total        used        free      shared  buff/cache   available
Mem:          30060        6100       23561           1         398       23565