I've been asked to help with a iMac showing the beachball and being very slow.
The problems started after installing security update 2019-002 and Safari 12.1.
The OS was Sierra (10.12) first, then updated to Mojave (10.14) which did not solve the problem.
I have a screenshot of Activity Monitor:
There I see Safari is using 30.31 GB of memory and 29.64 GB compressed memory, 8 threads, 358 ports.
Memory pressure is red, general information about memory is
8 GB physical
7.54 GB used
953.4 MB app
1.10 GB wired
5.50 GB compressed
459.3 MB cached files
662.0 MB swap
All accounts on that machine are affected.
I assume that heavy swapping is going on, slowing down the iMac. (I don't know whether it has a SSD or a HDD.)
However, what I don't understand and what puzzles me, is how Safari can use 30 GB of memory when there is only 8GB physical and only 662 MB swap space (that being "The space used on your startup drive by macOS memory management.").
That's my main question. But of course, any help on how to go about solving the problem is very much appreciated, too.