Make deflate-on-oom optional

Signed-off-by: Santtu Lakkala <santtu.lakkala@unikie.com>

Author: slakkala

lib/runners/cloud-hypervisor.nix

@@ -5,7 +5,7 @@
 
 let
   inherit (pkgs) lib;
-  inherit (microvmConfig) vcpu mem balloonMem user interfaces volumes shares socket devices hugepageMem graphics storeDisk storeOnDisk kernel initrdPath;
+  inherit (microvmConfig) vcpu mem balloonMem deflateOnOOM user interfaces volumes shares socket devices hugepageMem graphics storeDisk storeOnDisk kernel initrdPath;
   inherit (microvmConfig.cloud-hypervisor) extraArgs;
 
   kernelPath = {
@@ -54,8 +54,9 @@ let
 
   balloonOps = opsMapped {
     size = "${toString balloonMem}M";
-    deflate_on_oom = "on";
     free_page_reporting = "on";
+  } // lib.optionalAttrs deflateOnOOM {
+    deflate_on_oom = "on";
   };
 
   tapMultiQueue = vcpu > 1;

lib/runners/qemu.nix

@@ -39,7 +39,7 @@ let
   qemu = overrideQemu (if microvmConfig.cpu == null then
     pkgs.qemu_kvm else pkgs.buildPackages.qemu_full);
 
-  inherit (microvmConfig) hostName cpu vcpu mem balloonMem user interfaces shares socket forwardPorts devices vsock graphics storeOnDisk kernel initrdPath storeDisk;
+  inherit (microvmConfig) hostName cpu vcpu mem balloonMem deflateOnOOM user interfaces shares socket forwardPorts devices vsock graphics storeOnDisk kernel initrdPath storeDisk;
   inherit (microvmConfig.qemu) machine extraArgs serialConsole;
 
   inherit (import ../. { inherit (pkgs) lib; }) withDriveLetters;
@@ -208,7 +208,9 @@ lib.warnIf (mem == 2048) ''
     ] ++
     lib.optionals (user != null) [ "-user" user ] ++
     lib.optionals (socket != null) [ "-qmp" "unix:${socket},server,nowait" ] ++
-    lib.optionals (balloonMem > 0) [ "-device" "virtio-balloon,free-page-reporting=on,id=balloon0,deflate-on-oom=on" ] ++
+    lib.optionals (balloonMem > 0) [
+	 "-device" ("virtio-balloon,free-page-reporting=on,id=balloon0" + lib.optionalString (deflateOnOOM) ",deflate-on-oom=on")
+    ] ++
     builtins.concatMap ({ image, letter, serial, direct, readOnly, ... }:
       [ "-drive"
         "id=vd${letter},format=raw,file=${image},if=none,aio=io_uring,discard=unmap${

nixos-modules/microvm/options.nix

@@ -123,6 +123,15 @@ in
       type = types.int;
     };
 
+    deflateOnOOM = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        Whether to enable automatic balloon deflation on out-of-memory.
+      '';
+    };
+
+
     forwardPorts = mkOption {
       type = types.listOf
         (types.submodule {