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So this is about an old MacBook Pro - just old enough to have user replaceable memory.

The memory usage usually stays in the green, but the size of the Cached Files + Memory Used usually adds up to the total memory. My guess is the computer tries to keep some RAM free for working.

I notice some lag in switching apps when many are open - even though memory usage is in the green.

Does this warrant increasing the RAM to 16GB from 8?

Attached are pics - one from htop and another from the activity monitor, and another from top, to show the usage.

output of htop memory tab on activity monitor output of top

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In general, operating systems tend to work towards having "cache + memory used" equal the actual amount of physical memory. The more that is cached, the greater the likelihood that certain operations can be sped up.

In general having more RAM means that the operating system with the same work load is able to cache more things, which could potentially speed some operations up. It is not however an indicator that you "need" more RAM as such.

However, your screenshots does indicate that you're using 1.8 GB of swap. That could be an indicator that more RAM is necessary. Coupled with the fact that you experience a lag when switching apps - it does sound likely that more RAM could be helpful.

I would try using the Terminal and running the command top. It will show a list of processes running on your Mac, and at the top it will list the number of "swapins" and "swapouts". If you have top running in a visible window, and then try switching between the apps that you use - then check if the those two numbers start rising when you experience the lag. If that's the case, I think a RAM upgrade would most probably improve the situation.

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  • Good advice, thanks. Swap ins increase on opening almost every app. So why does the activity monitor show green the whole time? I know that when long back I had only 4GB it used to show yellow/red from time to time.. – Yogesch Sep 10 '20 at 8:42
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    This indicates that the system is doing OK memory wise right now - we're bringing stuff back from swap all the time. However, at some point earlier on, you must have done something that increased the number of swap outs a lot. I.e. right now, the computer is doing OK - but previously it was maxed out. I would continue monitoring until you hit something that increases swapouts! – jksoegaard Sep 10 '20 at 9:36
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    I would add that given the fact that you're over 80% utilized at this moment (assuming this is your "normal"), it would be prudent to add more memory. I like to keep my baseline at no more than 60 to 70% utilization so I always have room when resource needs spike which they inevitably do. – Allan Sep 10 '20 at 14:01
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    The swapping will especially slow you down if you still have a mechanical hard drive. I'd certainly go to 16 GB and replace the drive with an SSD. – Michael Hampton Sep 11 '20 at 2:38
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I would definitely recommend getting 16 GB for your Mac. It's a relatively cheap investment to increase the performance of your Mac by removing a possible bottleneck.

You don't say what OS you're on or what apps/tasks you do, but certainly my own experience is that 8 GB is somewhat limiting.

If you haven't already, you should also fit an SSD instead of the hard drive.

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