[vm] Fix HeapProfileSampler::SampleOldSpaceAllocation

When Isolate is just starting up and no TLABs are yet present we were setting interval_to_next_sample_ to -1 which caused every old space allocation to be sampled. This CL properly initializes the interval to sampling_interval_ instead. TEST=vm/cc/DartAPI_HeapSampling_CorrectSamplingIntervalForOldSpaceAllocations Change-Id: Ieb29234379d3afa4716ebdf3591f9fc0cbcaef71 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/311844 Commit-Queue: Slava Egorov <[email protected]> Commit-Queue: Martin Kustermann <[email protected]> Auto-Submit: Slava Egorov <[email protected]> Reviewed-by: Martin Kustermann <[email protected]>
dart-lang · Jun 28, 2023 · 86c3116 · 86c3116
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diff --git a/runtime/vm/dart_api_impl_test.cc b/runtime/vm/dart_api_impl_test.cc
@@ -10868,6 +10868,29 @@ TEST_CASE(DartAPI_HeapSampling_NonTrivialSamplingPeriod) {
   Dart_EnterIsolate(isolate);
   Dart_DisableHeapSampling();
 }
+
+// Check that we set correct sampling interval for old space allocations
+// during initial isolate startup (before the first TLAB is created).
+// This is a regression test for a bug that was causing each old space
+// allocation to be sampled.
+VM_UNIT_TEST_CASE(
+    DartAPI_HeapSampling_CorrectSamplingIntervalForOldSpaceAllocations) {
+  Dart_RegisterHeapSamplingCallback(
+      [](Dart_Isolate isolate, Dart_IsolateGroup isolate_group,
+         const char* cls_name, intptr_t allocation_size) -> void* {
+        // Should not be called because sampling interval is very large.
+        UNREACHABLE();
+        return nullptr;
+      },
+      [](void* data) {
+        // Nothing to do.
+      });
+  Dart_SetHeapSamplingPeriod(1 * GB);
+  Dart_EnableHeapSampling();
+  TestCase::CreateTestIsolate();
+  Dart_DisableHeapSampling();
+  Dart_ShutdownIsolate();
+}
 #endif  // !defined(PRODUCT) || defined(FORCE_INCLUDE_SAMPLING_HEAP_PROFILER)
 
 #if defined(DART_ENABLE_HEAP_SNAPSHOT_WRITER)

diff --git a/runtime/vm/heap/sampler.cc b/runtime/vm/heap/sampler.cc
@@ -248,6 +248,12 @@ void HeapProfileSampler::SampleOldSpaceAllocation(intptr_t allocation_size) {
     interval_to_next_sample_ = tlab_interval;
   }
 
+  // If we don't have a TLAB yet simply initialize interval_to_next_sample_
+  // from the sampling interval.
+  if (interval_to_next_sample_ == kUninitialized) {
+    interval_to_next_sample_ = sampling_interval_;
+  }
+
   // Check the allocation is large enough to trigger a sample. If not, tighten
   // the interval.
   if (allocation_size < interval_to_next_sample_) {