[prussian]

With zram, I can just use zram-generator[0] and it does everything for me and I don't even need to set anything up, other than installing the systemd generator, which on some distros, it's installed by default. Is there anything equivalent for zswap? Otherwise, I'm not surprised most people are just using zram, even if sub-optimal.

[0]: https://crates.io/crates/zram-generator

[ac29]

Zswap is enabled by default in Arch. Wont do anything without a backing disk swap though

[bilegeek]

Kernel arguments are the primary method: https://wiki.archlinux.org/title/Zswap#Using_kernel_boot_par...

Snag: I had issues getting it to use zstd at boot. Not sure if it's a bug or some peculiarity with Debian. Ended up compiling my own kernel for other reasons, and was finally able to get zstd by default, but otherwise I'd have to make/add it to a startup script.

[networked]

I had the same issue with LZ4. I found a thread about it on the Linux Mint Debian Edition forum and posted my fix there: https://forums.linuxmint.com/viewtopic.php?p=2767087#p276708....

In short: add the kernel modules and update GRUB as usual, then install sysfsutils and add the following line at the end of `/etc/sysfs.conf`:

  module/zswap/parameters/compressor = lz4
  # For zstd:
  #module/zswap/parameters/compressor = zstd

Perhaps some kernel change between Linux 6.8 and 6.12 caused the old approach to no longer work.

[alfanick]

This should've been a bash script...

[seba_dos1]

It's a handy tool, but it doesn't even give you a reasonable zram size by default and doesn't touch other things like page-cluster, so "I don't even need to set anything up" applies only if you don't mind it being quite far from optimal.

[melvyn2]

  echo 1 > /sys/module/zswap/parameters/enabled

It's in TFA.

[prussian]

enabling != configuring. Are you saying this is all that's necessary, assuming an existing swap device exists? That should be made clearer.

Edit: To be extra clear. When I was researching this, I ended up going with zram only because:

* It is the default for Fedora.

* zramctl gives me live statistics of used and compressed size.

* The zswap doc didn't help my confusion on how backing devices work (I guess they're any swapon'd device?)

[stdbrouw]

It doesn't really need any config on most distros, no.

That said, if you want it to behave at its best when OOM, it does help to tweak vm.swappiness, vm.watermark_scale_factor, vm.min_free_kbytes, vm.page-cluster and a couple of other parameters.

See e.g.

https://makedebianfunagainandlearnhowtodoothercoolstufftoo.c...

https://documentation.suse.com/sles/15-SP7/html/SLES-all/cha...

I don't know of any good statistics script for zswap, I use the script below as a custom waybar module:

  #!/bin/bash
  stored_pages="$(cat /sys/kernel/debug/zswap/stored_pages)"
  pool_total_size="$(cat /sys/kernel/debug/zswap/pool_total_size)"
  compressed_size_mib="$((pool_total_size / 1024 / 1024))"
  compressed_size_gib="$((pool_total_size / 1024 / 1024 / 1024))"
  compressed_size_mib_remainder="$((compressed_size_mib * 10 / 1024 - compressed_size_gib * 10))"
  uncompressed_size="$((stored_pages * 4096))"
  uncompressed_size_mib="$((uncompressed_size / 1024 / 1024))"
  uncompressed_size_gib="$((uncompressed_size / 1024 / 1024 / 1024))"
  uncompressed_size_mib_remainder="$((uncompressed_size_mib * 10 / 1024 - uncompressed_size_gib * 10))"
  ratio="$((100 * uncompressed_size / (pool_total_size + 1)))"
  echo "$compressed_size_gib.$compressed_size_mib_remainder"