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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!

The 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)?

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