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I remember years ago reading a textbook that stated significantly high page faults and other RAM-related issues can occur with constant utilization rates >= X%; it didn't necessary start at just 100%.
Is this true? If so, what is the metric on that?
8protons
Posted 2019-03-15T18:58:01.227
Reputation: 111
0
No.
The RAM utilization is intentionally kept as high as possible by the OS because you can't save RAM for later. So high utilization doesn't correlate with memory pressure or load of any kind. Modern operating systems choose a free RAM target (typically very small) and, even if under moderate load, generally maintain something very close to that target.
For example, suppose 50% of RAM is free and then some application starts reading lots and lots of files. The operating system will keep as much of that file data in memory as it can to reduce I/O if some other process wants to read that data or it will keep filesystem metadata in RAM. (Why shouldn't it? There's no cost to do and and there might be a benefit.) So the RAM utilization may shoot up from 50% to 98%, but that doesn't indicate any memory pressure or issue of any kind and more memory wouldn't provide any significant benefit.
David Schwartz
Posted 2019-03-15T18:58:01.227
Reputation: 58 310
3
A "page fault" isn't an issue as in corruption or damage... though it will impact performance. Page faults will start to occur as soon as requested data is no longer in RAM and needs to be retrieved from swap. Data can be pushed to swap for one of many reasons, including filesystem cache... so it's not even tied directly to the applications running.
– Attie – 2019-03-15T19:02:35.957It gets more complicated with memory compression. For instance, in modern MacOS or Windows 10, if you've got 15/16 GB used, and need another 2 GB, then the OS will first attempt to compress some of the used memory before using the relatively slow virtual memory. – Christopher Hostage – 2019-03-15T19:25:17.357