Re: [gentoo-user] 32GB RAM and Swap

[François-Xavier Carton]

On Sat, May 02, 2020 at 10:12:08PM +0800, William Kenworthy wrote:
> I am afraid this is an ".. it depends" question.
>

Yes, I agree.

> If you work with large images or data sets, swap can be really handy. 
> If you are doing a little programming, web browsing, reading email you
> will *probably* be ok, but why risk it?
>

Risk what? Having the OOM killer kill the problematic process? Depending
on your usage, this might be the best. Personally I prefer that to a
system that is stuck. I never had to force reboot on a system without
swap, whereas with swap I had to reboot most of the times swap was used.
Also it's super annoying when your system freezes because of a
background process swapping (eg. an emerge world update) while your
doing something else.

I've been running a 8GB system for a year, before that a 4GB system.
Both without swap. It's been fine so far. I did have processes killed
(eg. firefox compiling), but at least I can continue to use my system
without being interrupted by a freeze. It's a lot less frustrating to
have to resume a killed compilation than to deal with a frozen system.

> I have a 32gb ram in a master server for an mfs filesystem - it normally
> sits at about 5GB of ram - however it can go well over 32Gb into swap at
> times - the first machine I tried it with only had 4gb ram and crashed
> when it filled the ram, and 8g swap taking the test file system with it
> - its now production so I am not going to risk it by underprovisioning
> swap.  My 32Gb desktop is not using any swap at the moment ... but it
> has used it at times. 
>
> So, yes its quite likely you wont use swap - but if you do something
> that needs it, it can help avoid a very messy crash.
>
> Swap is slow, but if you actually need it - its probably critical that
> you have it!  Unless you are really short of disk space, treat it as
> insurance :)
>
> Look into using swapfiles instead of partitions for flexibility, and the
> sysctl values of "vm.swappiness" and "vm.vfs_cache_pressure" to manage
> swap usage (you can set to not use swap until it really has to - some
> have seen the kernel being too eager to swap out causing slowdowns,
> though you can make it go in the other direction and "thrash" when it
> actually needs to use swap if you go to far.  The default kernel swap
> mechanism isn't really that bad!
>

Swapfiles are great, because you can only add them when you need and
remove them when you're done. I sometimes use them when emerging large
stuff when I have other big processes in memory.

> So yes, most of my machines don't need swap *right now* and swap looks
> like its not being used so it could be removed, but I cant guarantee
> that they never will, and having years of experience using swap I
> recommend that its better to be cautious and survive :)

My systems usually survive (are not forcibly rebooted) better when there
is no swap. But I agree that in the end, it depends on the usage.