The atop man page says:
An occupation percentage of 90% is considered 'critical'. Notice that this occupation percentage is the accumulated memory consumption of the kernel (including slab) and all processes; the memory for the page cache ('cache' and 'buff' in the MEM-line) is not implied!
MEM line of our atop output looks like this:
MEM | tot 94.4G | free 252.4M | cache 70.1G |dirty 127.5M | buff 450.4M | slab 4.5G
I am trying to understand what the 70.1G of cache really refers to. One person I spoke with said it includes process virtual memory. However, when I searched for information on Linux Page Cache, I saw this:
Under Linux, the Page Cache accelerates many accesses to files on non volatile storage
which makes it sounds like it is really I/O storage related. In looking at virtual memory used by all the processes, I see about 70G allocated/used, which seems to correlate with the 70G from the atop output.
So is atop showing virtual memory usage, memory cache reserved for speeding file access (or maybe both)?