I have a mid-2010 iMac running High Sierra. It has started getting very sluggish several times a week. I have tracked it down to the memory pressure and the process kernal_task. Shown below is a screenshot of the activity monitor when this occurs.
As you can see the process kernal_task is using 9.43 GB of memory. This usually lasts 20 or 30 minutes. The kernal_task will occasionally drop to 5.46 GB and then sometimes down to 1.6 GB at which time the memory pressure is small and it turns green and my machine will return to normal.
The next image is of the Activity Monitor showing CPU usage. Kernal_task is not using a lot of CPU but has been running for quite a while.
Does anyone have an idea of what is happening?
I've tried restarting my computer and quitting all open apps when it gets sluggish. Restarting the computer worked but eventually it gets sluggish again. Restarting every time this happens is a real pain. Quitting the open apps seems to have no effect. The final image below shoes the memory pressure when things return to normal.