nixos/profiles/zramSwap.nix

   1 # Warning(perf): using zswap is almost always better, see:
   2 # https://chrisdown.name/2026/03/24/zswap-vs-zram-when-to-use-what.html
   3 { lib, ... }:
   4 with lib;
   5 {
   6   zramSwap = {
   7     enable = true;
   8     algorithm = mkDefault "zstd";
   9     # There is little point creating a zram greater
  10     # than twice the size of memory.
  11     memoryPercent = mkDefault 150;
  12     # Linux supports multithreaded compression for 1 device since 3.15.
  13     # See https://lkml.org/lkml/2014/2/28/404 for details.
  14     swapDevices = mkDefault 1;
  15   };
  16
  17   boot.kernel.sysctl = {
  18     # Increase cache pressure, which increases the tendency of the kernel to
  19     # reclaim memory used for caching of directory and inode objects. You will use
  20     # less memory over a longer period of time. The performance hit is negated by
  21     # the downside of swapping sooner.
  22     "vm.vfs_cache_pressure" = mkDefault 500;
  23
  24     # Increasing how aggressively the kernel will swap memory pages since we are
  25     # using ZRAM first.
  26     "vm.swappiness" = mkDefault 100;
  27
  28     # Background processes will start writing right away when it hits the 1% limit
  29     "vm.dirty_background_ratio" = mkDefault 1;
  30
  31     # The system won’t force synchronous I/O until it gets to 50% dirty_ratio.
  32     "vm.dirty_ratio" = mkDefault 50;
  33   };
  34 }