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fix: respect BUN_JSC_forceRAMSize in process.constrainedMemory() #25489

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fix: respect BUN_JSC_forceRAMSize in process.constrainedMemory() #25489

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fix: respect BUN_JSC_forceRAMSize in process.constrainedMemory()
KushalMeghani1644 Dec 12, 2025
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KushalMeghani1644 Dec 12, 2025
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1 change: 1 addition & 0 deletions bun.lock
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8 changes: 6 additions & 2 deletions src/bun.js/bindings/BunProcess.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -99,6 +99,8 @@ typedef int mode_t;
#include <JavaScriptCore/IntegrityInlines.h>
#endif

#include <JavaScriptCore/Options.h>

#pragma mark - Node.js Process

#if defined(__APPLE__)
Expand Down Expand Up @@ -1983,7 +1985,8 @@ static JSValue constructReportObjectComplete(VM& vm, Zig::GlobalObject* globalOb
heapSpaces->putDirect(vm, JSC::Identifier::fromString(vm, "shared_large_object_space"_s), JSC::constructEmptyObject(globalObject), 0);
RETURN_IF_EXCEPTION(scope, {});

heap->putDirect(vm, JSC::Identifier::fromString(vm, "totalMemory"_s), JSC::jsNumber(WTF::ramSize()), 0);
size_t ramSize = JSC::Options::forceRAMSize();
heap->putDirect(vm, JSC::Identifier::fromString(vm, "totalMemory"_s), JSC::jsNumber(ramSize ? ramSize : WTF::ramSize()), 0);
heap->putDirect(vm, JSC::Identifier::fromString(vm, "executableMemory"_s), jsNumber(0), 0);
heap->putDirect(vm, JSC::Identifier::fromString(vm, "totalCommittedMemory"_s), jsNumber(0), 0);
heap->putDirect(vm, JSC::Identifier::fromString(vm, "availableMemory"_s), jsNumber(0), 0);
Expand Down Expand Up @@ -3076,7 +3079,8 @@ static Process* getProcessObject(JSC::JSGlobalObject* lexicalGlobalObject, JSVal

JSC_DEFINE_HOST_FUNCTION(Process_functionConstrainedMemory, (JSC::JSGlobalObject * globalObject, JSC::CallFrame* callFrame))
{
return JSValue::encode(jsNumber(WTF::ramSize()));
size_t ramSize = JSC::Options::forceRAMSize();
return JSValue::encode(jsNumber(ramSize ? ramSize : WTF::ramSize()));
}

JSC_DEFINE_HOST_FUNCTION(Process_functionResourceUsage, (JSC::JSGlobalObject * globalObject, JSC::CallFrame* callFrame))
Expand Down
7 changes: 5 additions & 2 deletions src/bun.js/bindings/BunProcessReportObjectWindows.cpp
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Expand Up @@ -14,6 +14,7 @@
#include "JavaScriptCore/JSGlobalObject.h"
#include "JavaScriptCore/TopExceptionScope.h"
#include "JavaScriptCore/VM.h"
#include "JavaScriptCore/Options.h"
#include "wtf/text/WTFString.h"
#include "wtf/text/StringView.h"
#include "wtf/text/ASCIILiteral.h"
Expand Down Expand Up @@ -302,9 +303,11 @@ JSValue constructReportObjectWindows(VM& vm, Zig::GlobalObject* globalObject, Pr
heapSpaces->putDirect(vm, Identifier::fromString(vm, "shared_large_object_space"_s), constructEmptyObject(globalObject), 0);
heapSpaces->putDirect(vm, Identifier::fromString(vm, "trusted_large_object_space"_s), constructEmptyObject(globalObject), 0);

heap->putDirect(vm, Identifier::fromString(vm, "totalMemory"_s), jsNumber(WTF::ramSize()), 0);
const auto forcedRAMSize = JSC::Options::forceRAMSize();
const auto reportedRAMSize = forcedRAMSize ? forcedRAMSize : WTF::ramSize();
heap->putDirect(vm, Identifier::fromString(vm, "totalMemory"_s), jsNumber(reportedRAMSize), 0);
heap->putDirect(vm, Identifier::fromString(vm, "usedMemory"_s), jsNumber(vm.heap.size()), 0);
heap->putDirect(vm, Identifier::fromString(vm, "memoryLimit"_s), jsNumber(WTF::ramSize()), 0);
heap->putDirect(vm, Identifier::fromString(vm, "memoryLimit"_s), jsNumber(reportedRAMSize), 0);
heap->putDirect(vm, Identifier::fromString(vm, "heapSpaces"_s), heapSpaces, 0);

report->putDirect(vm, Identifier::fromString(vm, "javascriptHeap"_s), heap, 0);
Expand Down
26 changes: 26 additions & 0 deletions test/js/node/process/process.test.js
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Expand Up @@ -762,6 +762,32 @@ describe.concurrent(() => {
expect(process.constrainedMemory() >= 0).toBe(true);
});

it("process.constrainedMemory() respects BUN_JSC_forceRAMSize", async () => {
const forcedSize = 500_000_000;

await using proc = Bun.spawn({
cmd: [bunExe(), "-e", "console.log(process.constrainedMemory())"],
env: {
...bunEnv,
BUN_JSC_forceRAMSize: String(forcedSize),
},
stdout: "pipe",
stderr: "pipe",
});

const [stdout, stderr, exitCode] = await Promise.all([
new Response(proc.stdout).text(),
new Response(proc.stderr).text(),
proc.exited,
]);

expect(stderr).toBe("");
expect(exitCode).toBe(0);

const reportedSize = parseInt(stdout.trim(), 10);
expect(reportedSize).toBe(forcedSize);
});
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@coderabbitai coderabbitai bot Dec 12, 2025

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🧹 Nitpick | 🔵 Trivial

Good coverage for BUN_JSC_forceRAMSize → process.constrainedMemory().
Uses bunExe/bunEnv and isolates the behavior well.

If this test ever flakes in CI due to incidental stderr output, consider relaxing:

-    expect(stderr).toBe("");
+    expect(stderr).toBeEmpty();

(Or assert it doesn’t contain "error:" rather than being strictly empty.)

📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
it("process.constrainedMemory() respects BUN_JSC_forceRAMSize", async () => {
const forcedSize = 500_000_000;
await using proc = Bun.spawn({
cmd: [bunExe(), "-e", "console.log(process.constrainedMemory())"],
env: {
...bunEnv,
BUN_JSC_forceRAMSize: String(forcedSize),
},
stdout: "pipe",
stderr: "pipe",
});
const [stdout, stderr, exitCode] = await Promise.all([
new Response(proc.stdout).text(),
new Response(proc.stderr).text(),
proc.exited,
]);
expect(stderr).toBe("");
expect(exitCode).toBe(0);
const reportedSize = parseInt(stdout.trim(), 10);
expect(reportedSize).toBe(forcedSize);
});
it("process.constrainedMemory() respects BUN_JSC_forceRAMSize", async () => {
const forcedSize = 500_000_000;
await using proc = Bun.spawn({
cmd: [bunExe(), "-e", "console.log(process.constrainedMemory())"],
env: {
...bunEnv,
BUN_JSC_forceRAMSize: String(forcedSize),
},
stdout: "pipe",
stderr: "pipe",
});
const [stdout, stderr, exitCode] = await Promise.all([
new Response(proc.stdout).text(),
new Response(proc.stderr).text(),
proc.exited,
]);
expect(stderr).not.toContain("error:");
expect(exitCode).toBe(0);
const reportedSize = parseInt(stdout.trim(), 10);
expect(reportedSize).toBe(forcedSize);
});
🤖 Prompt for AI Agents 
In test/js/node/process/process.test.js around lines 763 to 787, the test
currently asserts stderr is exactly empty which can cause flakes if incidental
non-error output appears; change the assertion to be resilient by checking
stderr does not include the substring "error:" (e.g., replace
expect(stderr).toBe("") with expect(stderr).not.toContain("error:") after
trimming) so the test still fails on real errors but tolerates benign stderr
noise.


it("process.report", () => {
// TODO: write better tests
JSON.stringify(process.report.getReport(), null, 2);
Expand Down