[NO QA] perf: Increase initial Hermes heap size for faster startup and delay Young-Gen GC

patches/react-native/details.md

@@ -196,3 +196,17 @@
 - Upstream PR/issue: There won't be any upstream changes. We need to get rid of InteractionManager
 - E/App issue: https://github.com/Expensify/App/issues/71913
 - PR introducing patch: https://github.com/Expensify/App/pull/69535
+
+### [react-native+0.81.4+026+perf-increase-initial-heap-size.patch](react-native+0.81.4+026+perf-increase-initial-heap-size.patch)
+
+- Reason: This patch increases the initial heap size of the Hermes runtime. This allows us to disable Hermes Young-Gen Garbage Collection (GC) in a separate patch, which improves initial TTI and app startup time.
+- Upstream PR/issue: This is not intended to be upstreamed, since this is a low-level fix very specific to the Expensify app's requirements.
+- E/App issue: [#76859](https://github.com/Expensify/App/issues/76859)
+- PR introducing patch: [#76154](https://github.com/Expensify/App/pull/76154)
+
+### [react-native+0.81.4+027+perf-disable-hermes-young-gc-before-tti-reached.patch](react-native+0.81.4+027+perf-disable-hermes-young-gc-before-tti-reached.patch)
+
+- Reason: This patch disables Hermes Young-Gen Garbage Collection (GC), which improves initial TTI and app startup time, by delaying GC for early allocated memory to the first Old-Gen GC run. 
+- Upstream PR/issue: This is not intended to be upstreamed, since this is a low-level fix very specific to the Expensify app's requirements.
+- E/App issue: [#76859](https://github.com/Expensify/App/issues/76859)
+- PR introducing patch: [#76154](https://github.com/Expensify/App/pull/76154)

patches/react-native/react-native+0.81.4+026+perf-increase-initial-heap-size.patch

@@ -0,0 +1,13 @@
+diff --git a/node_modules/react-native/ReactCommon/react/runtime/hermes/HermesInstance.cpp b/node_modules/react-native/ReactCommon/react/runtime/hermes/HermesInstance.cpp
+index d09f3a7..9018067 100644
+--- a/node_modules/react-native/ReactCommon/react/runtime/hermes/HermesInstance.cpp
++++ b/node_modules/react-native/ReactCommon/react/runtime/hermes/HermesInstance.cpp
+@@ -126,6 +126,8 @@ std::unique_ptr<JSRuntime> HermesInstance::createJSRuntime(
+   assert(msgQueueThread != nullptr);
+
+   auto gcConfig = ::hermes::vm::GCConfig::Builder()
++                      .withInitHeapSize(150ll * 1024 * 1024)
++                      .withShouldReleaseUnused(::hermes::vm::kReleaseUnusedNone)
+                       // Default to 3GB
+                       .withMaxHeapSize(3072 << 20)
+                       .withName("RNBridgeless");

patches/react-native/react-native+0.81.4+027+perf-disable-hermes-young-gc-before-tti-reached.patch

@@ -0,0 +1,17 @@
+diff --git a/node_modules/react-native/ReactCommon/react/runtime/hermes/HermesInstance.cpp b/node_modules/react-native/ReactCommon/react/runtime/hermes/HermesInstance.cpp
+index 9018067..405a36f 100644
+--- a/node_modules/react-native/ReactCommon/react/runtime/hermes/HermesInstance.cpp
++++ b/node_modules/react-native/ReactCommon/react/runtime/hermes/HermesInstance.cpp
+@@ -132,7 +132,11 @@ std::unique_ptr<JSRuntime> HermesInstance::createJSRuntime(
+                       .withMaxHeapSize(3072 << 20)
+                       .withName("RNBridgeless");
+
+-  if (allocInOldGenBeforeTTI) {
++  // By enabling the `allocInOldGenBeforeTTI` flag, we prevent
++  // Hermes from running Young-Gen GC before TTI,
++  // which saves around 150-200ms on initial load.
++  // Once Old-Gen GC is triggered, it will enable Young-Gen GC again.
++  if (/*allocInOldGenBeforeTTI*/ true) {
+     // For the next two arguments: avoid GC before TTI
+     // by initializing the runtime to allocate directly
+     // in the old generation, but revert to normal