Memory understanding

[emilli_xill]

Hello!

Could you please explain next things:

1) I have HA cluster and free -k -t command shows:

           total             used          free            shared     buff/cache  available
Mem: 130515764  31369656  81154516  7876         17991592    95544868
Swap: 33554300    0                33554300
Total: 164070064   31369656 114708816

And I don't understand why used+free!=total. How can I find out the persentage of free memory based on this data? 🤔

2) Also I don't understand following:

fw ctl pstat

Virtual System Capacity Summary:
Physical memory used: 20% (22050 MB out of 108338 MB) - below watermark
Kernel memory used: 2% (2260 MB out of 108338 MB) - below watermark
Virtual memory used: 16% (20689 MB out of 124907 MB) - below watermark
Used: 19510 MB by FW, 1152 MB by zeco
Concurrent Connections: 51356 (Unlimited)
Aggressive Aging is enabled, not active

As far as I understand, virtual memory - is an area of memory on HDD which is used when RAM (physical memory) runs out. But there is a lot of space - 80%..why virtual memory is used?

What is kernel memory? I know about FW and OS memory in CP, but not about kernel..

I will be very grateful for clarifications! 🙂 thank you

[PhoneBoy]

Total memory is not just free plus used, but also includes shared and buff/cache.
Note that buff/cache is memory that is allocated for something else currently, but can be allocated to another purpose if required.
To determine percentage of free memory available, therefore, use available divided by free.

In the context of fw ctl pstat, I'm not sure what Virtual Memory refers to.
There's no mention of it in the documentation in current versions, which suggests you might be doing this on an older version of code.

Kernel memory refers to the amount of memory used by various gateway functions that must be done in the kernel (versus, say, a specific userspace process you'd see with ps or top output).
Anything in kernel memory cannot be "swapped" out as a result of more memory being required by a userspace process.
If a kernel process needs more memory and doesn't have it, a kernel panic will occur.