I'm aware what compressed memory is from answers like this and Apple support but what I can't find is what exactly the usage means.
Take my system right now:
Is it telling me the top process is using 3.34GB of RAM and 3.26GB compressed, or is it telling me it is using 3.34GB of memory in total, of which 3.26GB is compressed?
Is there any way to understand how much compression is going on i.e. what that 3.26GB was before compression?
Best Answer
I have had trouble finding documentation that is from Apple that clearly lays out the difference between looking at the compressed memory for a process, versus looking at the total amount of compressed memory in the Memory tab. Their support document speaks only to the latter.
That said, I have never seen the compressed memory for an individual process be more than the process, but I have seen it be exactly equal to the memory of a process. This suggests to me that compressed memory is telling you how much of the total memory of an app is compressed. Otherwise I'd expect there to be at least some cases where a process that was mostly dormant might have more total compressed memory than uncompressed.
However the amount of total compressed memory is considered an addition to the total app memory when calculating the total memory used categories on the Memory tab.