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Comment by Aurornis | Hacker News Reader

> We were seeing average 88% memory usage

My 64GB MacBook Pro sits around that level after using it for a while, too. So do my Windows and Linux machines even with different amounts of RAM.

There's a popular page explaining it for Linux, but it's applicable to every OS: https://www.linuxatemyram.com/

Isolated RAM usage numbers aren't useful because spare memory is used for caching. Even if you are using 88% of the RAM, that's not indicative of a problem unless you're encountering a lot of swapping. Even swapping a little bit isn't bad if it's not stalling the machine out. You have to look at actual performance, not RAM usage percentages.

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I’ve had to explain too many times to people who should know better that “rss” is not how much memory a process needs but how much the operating system allows it to have. Put other stuff on the machine and that number will go down. No it’s not that improvement you think you made to that data structure. If you want that, look at total memory or heap size after GC if it’s a garbage collected language.

I don't understand why the default way to show RAM usage on Linux isn't to simply show "In Use vs. Available".

I don't care how much cache is being used and I can't really do anything about it even if I did.

Cache is super important though. Not having enough memory for cache will tank your system performance, even if you have a ton of "available" memory

I'm not saying it's not important. It's that I don't have any control over it. Do I have enough "cache" in your opinion? Presently I have: Used: 14.6 Avail: 16.6 Cache: 4.2 Free: 6.4

If I'm asking the question "Is my system starved of RAM?" I am going to look at USED and AVAIL. CACHE is a curiosity more than anything else and FREE tells me nothing.

Also, under what circumstances would I have a ton of AVAIL and be starving the CACHE? That's an OS/kernel problem. If AVAIL drops to zero I can expect to get OOM crashing pretty quick.

atop (one of the many variants of top) reports numbers for "free", "available", and "cache" in its total systems report. As long as "available" is high, I don't worry about the RAM.

My 32 GB MacBook Pro sits at about 50%, even after months of being powered on, unless I'm running programs that use a lot of memory. That's at least what Activity Monitor reports, perhaps Activity Monitor reports it in a different way.

I truly hate, more than anything else in the tech discourse, that this gets trotted out every time the discussion of RAM comes up. "unUsED rAM iS wASTED RAm", always used to defend and justify abhorrent and incompetent software development practices. Even with 32gb, I routinely run into out-of-memory crashes on a near-daily basis with workloads that should not in principle be anywhere near that usage.

If they were making decisions based on RAM, they were almost certainly encountering real-world issues which prompted looking at their usage statistics in the first place, rather than just looking up their RAM usage metrics for funsies.

This is talk about how the OS uses that RAM to make your software better.

But to that point, having to explain to people why this 32GB machine with two processes using 10GB each can not, in fact, fit another 10GB process because the response times of the two existing processes relies heavily on that “unused” memory that is actually part of the working set of the machine. And also occasionally one of those services spikes to 14GB so what happens when that happens?

So in that regard showing that memory as used has advantages for avoiding arguments with people who are not equipped to have their half of the argument in a useful and meaningful way.

I think the point is not that one should not look at RAM use, but be careful when looking at it since total RAM use may include the amount that is used for disk cache which will fill to use whatever is available (and will be freed back if necessary).

It makes sense to watch memory use but one should make sure to discount the amount used for disk caching from the total.

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