nixos/zram: add zramSwap.memoryMax option

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 commit is contained in:
Luke Granger-Brown 2020-11-05 02:29:46 +00:00
parent db63be9c91
commit ad62155cb6

View File

@ -80,6 +80,15 @@ in
'';
};
memoryMax = mkOption {
default = null;
type = with types; nullOr int;
description = ''
Maximum total amount of memory (in bytes) that can be used by the zram
swap devices.
'';
};
priority = mkOption {
default = 5;
type = types.int;
@ -146,7 +155,12 @@ in
# Calculate memory to use for zram
mem=$(${pkgs.gawk}/bin/awk '/MemTotal: / {
print int($2*${toString cfg.memoryPercent}/100.0/${toString devicesCount}*1024)
value=int($2*${toString cfg.memoryPercent}/100.0/${toString devicesCount}*1024);
${lib.optionalString (cfg.memoryMax != null) ''
memory_max=int(${toString cfg.memoryMax}/${toString devicesCount});
if (value > memory_max) { value = memory_max }
''}
print value
}' /proc/meminfo)
${pkgs.util-linux}/sbin/zramctl --size $mem --algorithm ${cfg.algorithm} /dev/${dev}