On 6/16/19 7:02 PM, Wols Lists wrote:
So you didn't read what I wrote ... Par for the course :-(
I did. I still hear people say it today. It's not old as in past tense.
The basic Unix mechanism needs twice ram.
I disagree.
It's inherent in the design of the thing. Whether linux no longer
uses the Unix mechanism, or it's had the hell optimised out of it I
don't know.
Either way, machines today get by on precious little swap - that's
fine.
Historic note - the early linux 2.4 vanilla kernels enforced the twice
ram rule - a lot of people who didn't read the release notes got nasty
shocks when their machines locked up the moment they touched swap ...
I disagree because I ran 2.0, 2.2, 2.4, and 2.6 kernels without swap
being twice the ram or greater. Swap did get used. They did not crash
when accessing swap.
And okay my machine only has 16GB of ram (and 64GB of swap - 32GB
each across two disks), but I'm pretty sure that if I followed your
guidelines, an emerge would crash my system as the tmpfs ran out of
space ...
I doubt it.
I've routinely done emerges on machines with < 16 GB of memory and 2 GB
of swap. Including llvm, clang, gcc, rust, Firefox and Thunderbird.
I routinely do an emerge -DuNe @world on a VPS with 1 GB of memory and 1
GB of swap. It works just fine. If I want to speed things up I enlarge
the VPS to 2 GB of memory and 1 GB of swap. Granted, it doesn't try to
compile things like Firefox and Thunderbird, thus Rust.
And those people who wrote your guidelines?
I just looked again, and Red Hat has lowered their recommendation from
what I remember from a few years ago.
Link - Table 15.1. Recommended System Swap Space
-
https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/storage_administration_guide/ch-swapspace#tb-recommended-system-swap-space
RAM ≤ 2 GB = swap should be 2 times the amount of RAM
2 < RAM ≤ 8 GB = swap should be equal to the amount of RAM
8 < RAM ≤ 64 GB = swap should be at least 4 GB
64 < RAM = swap should be at least 4 GB
Are they the same clueless people who believe the twice ram rule is
pure fiction?
I don't consider Red Hat's official statement to be "clueless".
Seeing as how their rules include "twice the RAM" in the first
condition, I don't think they thought it was pure fiction.
(As I said, it is *historical* *fact*).
I question the validity of that statement.
And why should I believe people who tell me the rule no longer
applies, if they can't tell me WHY it no longer applies? I'd love
to be enlightened - why can't anybody do that?
I'm not saying you should believe people.
My opinion is that the 2 x RAM no longer applies because systems don't
utilize swap space. As such it's a waste of disk space to dedicate 2 x
RAM to swap.
Look at the output of free. Or better, run sysstat / SAR and watch swap
usage. How much does your system use? How much disk space to you want
to dedicate to something that's likely hardly being touched.
Do what you want.
But be prepared to put the shoe on the other foot and explain why you
think that you should have 2 x RAM on each disk.
