From ad62155cb65a9aa0153dbde5be8698b715003473 Mon Sep 17 00:00:00 2001 From: Luke Granger-Brown Date: Thu, 5 Nov 2020 02:29:46 +0000 Subject: [PATCH] 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. --- nixos/modules/config/zram.nix | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/nixos/modules/config/zram.nix b/nixos/modules/config/zram.nix index 341101bc184..1f513b7e4da 100644 --- a/nixos/modules/config/zram.nix +++ b/nixos/modules/config/zram.nix @@ -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}