heap: Force incremental marking in C++ only workloads

... when above a certain minimum threshold. This is to guard against
memory running away in scenarios where the JS heap is empty and
there's only high throughput C++ allocations that don't allow for a
memory reducer GC to kick in.

This logic should be revisited after Oilpan's young generation
collector is implemented which may allow switching to a more efficient
shrinking strategy for initial heap setup.

Bug: chromium:1029379, chromium:1300028, chromium:1300492
Change-Id: I93924fc2fe77d6226c29358d3afb1cc9d6fbf3b1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3484319Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79255}

src/heap/heap.cc

@@ -5576,9 +5576,28 @@ Heap::IncrementalMarkingLimit Heap::IncrementalMarkingLimitReached() {
         !old_generation_size_configured_ && gc_count_ == 0) {
       // At this point the embedder memory is above the activation
       // threshold. No GC happened so far and it's thus unlikely to get a
-      // configured heap any time soon. Start a memory reducer in this case
-      // which will wait until the allocation rate is low to trigger garbage
-      // collection.
+      // configured heap any time soon.
+      //
+      // TODO(chromium:1029379): Revisit initial heap configuration when Oilpan
+      // run minor GCs as that would allow using a shrinking logic similar to
+      // V8.
+      if (global_memory_available) {
+        const size_t embedder_allocated_memory =
+            global_memory_available.value() - old_generation_space_available;
+        constexpr size_t kEmbedderMemoryThresholdToForceIncrementalGC =
+            32u * MB;
+        if (embedder_allocated_memory >
+            kEmbedderMemoryThresholdToForceIncrementalGC) {
+          // If we didn't get a garbage collection within allocating
+          // `kEmbedderMemoryThresholdToForceIncrementalGC` of memory this means
+          // that the embedder is still in high allocation rate. We cannot
+          // expect it to run idle soon but need to configure the heap somehow.
+          return IncrementalMarkingLimit::kHardLimit;
+        }
+      }
+      // Start a memory reducer in case the hard limit for embedder allocated
+      // memory has not been hit yet which will wait until the allocation rate
+      // is low to trigger garbage collection.
       return IncrementalMarkingLimit::kFallbackForEmbedderLimit;
     }
     return IncrementalMarkingLimit::kNoLimit;