Default Swap is too low

[CaptainN]

I love Bazzite! But the default swap size is FAR too low. It's only set to a max of 25% of RAM or 4GB (whichever is larger). This caused a LOT of instability on my systems, which had 16GB or 8GB or system RAM - it caused stutters even in gaming (compared with Windows on the same machine).

On my desktop I upgraded the RAM to 32GB to solve the stuttering and instability issues in games, but on my laptops (16GB and 8GB) the results was that just running a few apps for a while (maybe an hour) would produce so much memory pressure that it would crash the entire kernel. It would do so faster on the 8GB machine, obviously. (On my desktop, I set zram to 50% ram, so 16G, but based on some comments in PR #2202 I might lower that to 8G.)

I recommend drastically increasing the swap profile. At least bump it to 50% or 8G. On my 16GB system, I increased zram to ram *1 (and set the compressor to zstd) - and it completely solved the stability issues. On my 8GB system I went for something less conventional, and increased the zram to RAM * 1 (7.5G of zram) with a priority of 100, and added an 8GB disk swap with a priority of 10, since I'm not convinced zram would be enough under any kind of pressure. I'm still testing that laptop, but so far so good. I might eventually add even more disk swap (I'm also questioning RAM * 1 for zram, but trying it for now.)

TLDR: The default swap needs to be higher, and maybe add a disk swap as backup.

BTW, this is like a P1 problem to me - this issue caused hard locks on all three of the systems I run Bazzite on, and 16GB of system RAM isn't so unusual.

[KyleGospo]

Increased to /2, max 4096 from /4, max 4096. This fixes 8GB of ram setups but does not change how 16GB and up devices work.

We will not consider a swap file under any circumstance.

[CaptainN]

What I'm saying though is that I was seeing regular crashes, with kind of normal, web developer-ish type activity. A browser, and editor and some tools. Yes, that's memory intense, but not that much, and it was causing hard locks, just from running out of memory.

I think 4GB of zram just isn't enough on a 16GB machine. I increased it to 8GB, and haven't seen any crashes since. (I'm running a 1 to 1 on the 8GB machine, with 16GB of file swap - though it hasn't laid off to file swap even once yet.)

I think I understand not wanting to go with a swap file, but is there an explanation I can find anywhere, just out of curiosity?

(Switching to zstd may also have helped with my memory pressure.)

[CaptainN]

For what it's worth, CachyOS seems to use a 1:1 ram ratio, and zstd (or at least, they seem to recommend that in their docs).

Source: https://wiki.cachyos.org/features/cachyos_settings/#other-configurations

[CaptainN]

8GB makes sense - potentially even if you have only 8GB total RAM.

Steam OS on Steam Deck now does the following, for what it's worth:

[zram0]
# size at 50% of physical RAM (after discounting memory used by the kernel)
zram-size = ram/2
compression-algorithm = zstd
swap-priority = 100
fs-type = swap

• 50% of 16GB on the Steam Deck (or 15GB with default GPU allocation of 1GB) - so a little less than 8GB
  • The note at the top is in Valve's config, I didn't add it, and it's technically incorrect. It's half of system RAM minus GPU allocation, not kernel usage. That's why you get 7.5GB - if you set GPU allocation to 4GB, you'd get 6GB, etc.
  • IMHO it should just be set to 8GB (4GB is not enough,) when there's enough RAM for it (revised from previous statements.)
• They use zstd - more compression than what bazzite uses by default.
• They also set a file swap equal to total memory, to avoid crashes more completely - but they also set it to a negative priority:

Filename        Type        Size      Used  Priority
/dev/zram0      partition   7582204   0     100
/home/swapfile  file        16777212  0     -2

I know Bazzite devs want to avoid fileswap (without a reason stated) - that intuitively makes sense, but I've had real crashes from running out of memory, on all systems with 16GB of memory or less (3 of them,) and that's a bad look. The defaults inherited from Silverblue are also clearly server derived Red Hat defaults, not workstation class defaults.

[brianx87]

Reconfiguring the zram-generator.conf has fixed my system locking up. My previous algorithm was lz4, everything works great now without locking up using my new settings below.

[zram0] 
compression-algorithm = zstd
zram-size = 8192
swap-priority = 100
fs-type = swap

[CaptainN]

Quick update: The default on Fedora was actually moved up to min(ram, 8192) a while back - in Fedora 34. That seems like the perfect sweet spot for performance and stability.

[zram0] 
zram-size = min(ram, 8192)
compression-algorithm = zstd
swap-priority = 100

Refs:
https://docs.fedoraproject.org/en-US/fedora/f34/release-notes/sysadmin/Distribution/
https://fedoraproject.org/wiki/Changes/Scale_ZRAM_to_full_memory_size
https://discussion.fedoraproject.org/t/make-all-of-ram-be-zram/130286
https://www.phoronix.com/news/Fedora-34-zRAM-Tuning

[Zeglius]

With commit 8467af3, now it uses half physical ram, or 16GB (clamping to the smallest value)

[CaptainN]

That means on a machine with 8GB RAM, it'll only allocate 4GB zram - that's not enough (we will still see crashes), especially when the RAM specs are listed at 8GB minimum on the site. Still, this is an improvement for 16GB+, so that's something. Thanks!

Also, the commit says, "feat: Sync zram setting with SteamOS" - really? That's not what I found (see above), did they change it?