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https://github.com/ryan4yin/nix-config.git
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Ryan Yin
4b7375c077
The zram module was auto-imported on all hosts via base scanPaths, and its swappiness=180/page-cluster=0 tunings leaked onto hosts that disabled zram (e.g. idols-ai with a disk swapfile, pushing cold anon pages to disk swap). Wrap the whole module in modules.zram.enable (default true); idols-ai now turns off zram and its tunings with a single switch.
69 lines
3.0 KiB
Nix
69 lines
3.0 KiB
Nix
{
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lib,
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config,
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...
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}:
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let
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cfg = config.modules.zram;
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in
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{
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options.modules.zram.enable =
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lib.mkEnableOption ''
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zram in-memory swap device plus kernel sysctl tunings for it.
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The sysctl tunings (swappiness=180 etc.) are designed for in-memory swap
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devices only; they are gated behind this switch so that hosts which
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disable zram (e.g. using a disk swapfile instead) also revert to the
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kernel default swappiness instead of leaking zram tunings onto disk swap.
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Enabled by default; hosts that want disk-only swap should set it to false.
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''
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// {
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default = true;
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};
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config = lib.mkIf cfg.enable {
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# Enable in-memory compressed devices and swap space provided by the zram kernel module.
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# By enable this, we can store more data in memory instead of fallback to disk-based swap devices directly,
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# and thus improve I/O performance when we have a lot of memory.
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#
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# https://www.kernel.org/doc/Documentation/blockdev/zram.txt
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zramSwap = {
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enable = true;
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# one of "lzo", "lz4", "zstd"
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algorithm = lib.mkDefault "zstd";
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# Priority of the zram swap devices.
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# It should be a number higher than the priority of your disk-based swap devices
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# (so that the system will fill the zram swap devices before falling back to disk swap).
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priority = lib.mkDefault 100;
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# Maximum total amount of memory that can be stored in the zram swap devices (as a percentage of your total memory).
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# Defaults to 1/2 of your total RAM. Run zramctl to check how good memory is compressed.
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# This doesn't define how much memory will be used by the zram swap devices.
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memoryPercent = lib.mkDefault 50;
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};
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# Optimizing swap on zram
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boot.kernel.sysctl = {
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# vm.swappiness - Controls kernel preference for swapping (range: 0-200, default: 60)
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# For in-memory swap devices like zram/zswap, values above 100 are recommended.
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"vm.swappiness" = lib.mkDefault 180;
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# vm.watermark_boost_factor - Controls aggressiveness of memory reclaim (default: 15000)
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# Setting to 0 disables watermark boost, preventing premature memory reclamation.
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# This allows fuller memory utilization before the kernel starts reclaiming.
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"vm.watermark_boost_factor" = lib.mkDefault 0;
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# vm.watermark_scale_factor - Controls kswapd wakeup frequency (range: 1-1000, default: 10)
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# A higher value triggers background memory reclamation earlier (at 12.5% memory pressure).
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# Value 125 means kswapd becomes active when free memory drops below 1/125 of total memory,
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# balancing memory more proactively to prevent sudden swap storms at high swappiness values.
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"vm.watermark_scale_factor" = lib.mkDefault 125;
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# vm.page-cluster - Controls swap readahead (range: 0-6, default: 3)
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# 0 means read only 1 page (2^0) at a time, disabling readahead.
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# For low-latency devices like zram, readahead hurts performance by fetching unnecessary data.
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"vm.page-cluster" = lib.mkDefault 0;
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};
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};
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}
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