the conversion procedure is simple:
- find all things that look like options, ie calls to either `mkOption`
or `lib.mkOption` that take an attrset. remember the attrset as the
option
- for all options, find a `description` attribute who's value is not a
call to `mdDoc` or `lib.mdDoc`
- textually convert the entire value of the attribute to MD with a few
simple regexes (the set from mdize-module.sh)
- if the change produced a change in the manual output, discard
- if the change kept the manual unchanged, add some text to the
description to make sure we've actually found an option. if the
manual changes this time, keep the converted description
this procedure converts 80% of nixos options to markdown. around 2000
options remain to be inspected, but most of those fail the "does not
change the manual output check": currently the MD conversion process
does not faithfully convert docbook tags like <code> and <package>, so
any option using such tags will not be converted at all.
This allows capping the total amount of memory that will be used for
zram-swap, in addition to the percentage-based calculation, which is
useful when blanket-applying a configuration to many machines.
This is based off the strategy used by Fedora for their rollout of
zram-swap-by-default in Fedora 33
(https://fedoraproject.org/wiki/Changes/SwapOnZRAM), which caps the
maximum amount of memory used for zram at 4GiB.
In future it might be good to port this to the systemd zram-generator,
instead of using this separate infrastructure.
This creates a dependency cycle when used with boot.tmpOnTmpfs:
basic.target <- tmp.mount <- swap.target <- zram-init-dev0 <- basic.target
This same fix is done already for tmp.mount
Fixes https://github.com/NixOS/nixpkgs/issues/47474
- add `zramSwap.algorithm` option, which allows to change compressor
declaratively. zstd as default
- add `zramSwap.swapDevices` option, which allows to define how many zram
devices will be used as swap. Rest devices can be managed freely
- simpler floating calculations
- fix udev race condition
- some documentation changes
- replaced `/sys/block/zram*` handling with `zramctl`, because I had occasional
"Device is busy" error (looks like zram has to be configured in predefined order)
- added `memoryPercent` and `algorithm` as restart triggers. I think, it was
a bug that changing `memoryPercent` in configuration wasn't applied immediately.
- removed a bind to .swap device. While it looks natural (when swap device goes
off, so should zram device), it wasn't implemented properly. This caused problems
with swapon/swapoff:
```
$ cat /proc/swaps
Filename Type Size Used Priority
/dev/zram0 partition 8166024 0 -2
/var/swapfile file 5119996 5120 1
$ sudo swapoff -a
$ sudo swapon -a
swapon: /dev/zram0: read swap header failed
$ cat /proc/swaps
Filename Type Size Used Priority
/var/swapfile file 5119996 0 1
```
This allows you to use the Linux kernel's built-in compressed memory as
swap space functionality.
It is recommended to enable only for kernel 3.14 (which is when zram came out of
the staging drivers area) or higher.
