Allow customizing the scaling threshold with an environment variable

src/environment.ts

@@ -37,6 +37,12 @@ export enum EnvVar {
 
   ODASA_TRACER_CONFIGURATION = "ODASA_TRACER_CONFIGURATION",
 
+  /**
+   * What percentage of the total amount of RAM over 8 GB that the Action should reserve for the
+   * system.
+   */
+  SCALING_RESERVED_RAM_PERCENTAGE = "CODEQL_ACTION_SCALING_RESERVED_RAM_PERCENTAGE",
+
   /** Whether to suppress the warning if the current CLI will soon be unsupported. */
   SUPPRESS_DEPRECATED_SOON_WARNING = "CODEQL_ACTION_SUPPRESS_DEPRECATED_SOON_WARNING",
 

src/util.test.ts

@@ -4,6 +4,7 @@ import path from "path";
 
 import test from "ava";
 
+import { EnvVar } from "./environment";
 import { getRunnerLogger } from "./logging";
 import { getRecordingLogger, LoggedMessage, setupTests } from "./testing-utils";
 import * as util from "./util";
@@ -62,6 +63,14 @@ const GET_MEMORY_FLAG_TESTS = [
     expectedMemoryValue: 62.5 * 1024,
     expectedMemoryValueWithScaling: 61132, // Math.floor(1024 * (64 - 1.5 - 0.05 * (64 - 8)))
   },
+  {
+    input: undefined,
+    totalMemoryMb: 64 * 1024,
+    platform: "linux",
+    expectedMemoryValue: 63 * 1024,
+    expectedMemoryValueWithScaling: 58777, // Math.floor(1024 * (64 - 1 - 0.1 * (64 - 8)))
+    reservedPercentageValue: "10",
+  },
 ];
 
 for (const {
@@ -70,13 +79,20 @@ for (const {
   platform,
   expectedMemoryValue,
   expectedMemoryValueWithScaling,
+  reservedPercentageValue,
 } of GET_MEMORY_FLAG_TESTS) {
   test(
     `Memory flag value is ${expectedMemoryValue} without scaling and ${expectedMemoryValueWithScaling} with scaling ` +
       `for ${
         input ?? "no user input"
-      } on ${platform} with ${totalMemoryMb} MB total system RAM`,
+      } on ${platform} with ${totalMemoryMb} MB total system RAM${
+        reservedPercentageValue
+          ? ` and reserved percentage env var set to ${reservedPercentageValue}`
+          : ""
+      }`,
     async (t) => {
+      process.env[EnvVar.SCALING_RESERVED_RAM_PERCENTAGE] =
+        reservedPercentageValue || undefined;
       for (const withScaling of [true, false]) {
         const flag = util.getMemoryFlagValueForPlatform(
           input,

src/util.ts

@@ -37,6 +37,11 @@ export const DEFAULT_DEBUG_ARTIFACT_NAME = "debug-artifacts";
  */
 export const DEFAULT_DEBUG_DATABASE_NAME = "db";
 
+/**
+ * The default fraction of the total RAM above 8 GB that should be reserved for the system.
+ */
+const DEFAULT_RESERVED_RAM_SCALING_FACTOR = 0.05;
+
 export interface SarifFile {
   version?: string | null;
   runs: SarifRun[];
@@ -161,15 +166,28 @@ function getSystemReservedMemoryMegaBytes(
   const fixedAmount = 1024 * (platform === "win32" ? 1.5 : 1);
 
   if (isScalingReservedRamEnabled) {
-    // Reserve an additional 5% of the amount of memory above 8 GB, since the amount used by the
-    // kernel for page tables scales with the size of physical memory.
-    const scaledAmount = 0.05 * Math.max(totalMemoryMegaBytes - 8 * 1024, 0);
+    // Reserve an additional percentage of the amount of memory above 8 GB, since the amount used by
+    // the kernel for page tables scales with the size of physical memory.
+    const scaledAmount =
+      getReservedRamScaleFactor() *
+      Math.max(totalMemoryMegaBytes - 8 * 1024, 0);
     return fixedAmount + scaledAmount;
   } else {
     return fixedAmount;
   }
 }
 
+function getReservedRamScaleFactor(): number {
+  const envVar = Number.parseInt(
+    process.env[EnvVar.SCALING_RESERVED_RAM_PERCENTAGE] || "",
+    10,
+  );
+  if (envVar < 0 || envVar > 100 || Number.isNaN(envVar)) {
+    return DEFAULT_RESERVED_RAM_SCALING_FACTOR;
+  }
+  return envVar / 100;
+}
+
 /**
  * Get the value of the codeql `--ram` flag as configured by the `ram` input.
  * If no value was specified, the total available memory will be used minus a