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Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).

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ZRAM is insane (www.kernel.org)

submitted 1 year ago* (last edited 1 year ago) by [email protected] to c/[email protected]

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I got a cheap netbook style laptop for traveling some weeks ago (HP Stream 11" with 4 GB of RAM and a N4120). Didn't expect much more from this hardware than opening a few browser tabs and doing some retro gaming via Steam.

Shared RAM with graphics card means that 3.64 GB of RAM are effectively usable for the OS. This was even too little RAM to open a handful of tabs w/o having tabs being unresponsive for seconds sometimes in a very annoying way. Another thing which made trouble was the Wifi - I guess it went into power saving, was swapped and didn't load fast enough to provide a good experience. (Of course I wasted an hour checking for Wifi drivers/support.)

In short: Even for my low expectations for this laptop it was an underwhelming experience.

First step was to look at my vm.swappiness and set it to 10, which already helped, but still the machine had hiccups and annoying timeouts.

In a last, desperate effort I enabled ZRAM on the laptop... and literally WTF: Saying it is a night and day difference doesn't do the experience justice. Typing this words now on the Stream, which I use exactly the same way as my much more beefy other machines (my next worst computer has 8G of RAM and an Intel Core i3), browsing with 10 open tabs, e-mail client open on another virtual desktop... it is crazy, it makes the Stream fun to use and I use it at home for everything which isn't heavily CPU/IO bound.

What surprised me the most: No hiccups, no timeouts and it even fixed the Wifi issues on this little machine. Didn't expect this would be possible, especially with a N4120 and 3.64 GB of RAM.

In short, my laptop changed from not even reaching my low/realistic expectations to being my favorite technical purchase of the last years, thanks to ZRAM.

Besides making this a ZRAM appreciation post, I really want to spread the word about it. Especially for old hardware and limited RAM situations, IMHO it should be the first thing which comes to mind/is recommended.

Fedora and PopOS use it by default, so it is well tested and should IMHO again, be a default at least for desktop setups.

Give it a try - supposedly it even improved the experience on much more beefy computers for gaming etc.

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[–] chellomere 37 points 1 year ago (10 children)

I'm running ZRAM on my old Netgear ReadyNAS's, which has 512MB or 256MB RAM. It enables them to do a lot more than they otherwise would be able to, running a modern linux distribution.

I've been so satisfied with it that I even started running it on my modern desktop with 32GB RAM, it helps with my tab addiction :)

[–] [email protected] 20 points 1 year ago (9 children)

Rolling out ZRAM to all my boxes right now! 🙃

Do you also tweak other settings for ZRAM? According to ArchWiki PopOS settled for the following settings:

vm.swappiness = 180
vm.watermark_boost_factor = 0
vm.watermark_scale_factor = 125
vm.page-cluster = 0

I am testing this settings right now and cannot say I experience a difference compared to the defaults.

[–] [email protected] 4 points 1 year ago (3 children)

vm.swappiness value should be between 0 and 100 IIRC.

[–] Zadeis 11 points 1 year ago (1 children)

Kernel 5.8 changed this, so the value is from 0 to 200.

https://docs.kernel.org/admin-guide/sysctl/vm.html#swappiness

[–] [email protected] 1 points 1 year ago

Yes. I stand corrected.

So the kernel memory management system wants to free up some RAM... it'll either kick stuff out of the page cache (this is the disk cache), or write some stuff out to swap. vm.swappiness determines "relative I/O cost" of swapping something out versus dropping some disk cache (i.e. how much you think it'll slow the system down.) Total value is 200, so default vm.swappiness=60 means page cache is 140 (200-60). 140/60=2.33, so it considers regular disk I/o to be about 2.33 times the speed of swap. Settings vm.swappiness=100 means swap and disk I/O are equally fast; on modern kernels, in case you had a fast swap system (like some auxillary RAM disk or optane ssds or something) you can even set vm.swappiness over 100 to say 150 to say swap is faster than your regular disk.

https://stackoverflow.com/questions/72544562/what-is-vm-swappiness-a-percentage-of

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