[zone] Fix peak memory accounting

When switching from atomicops to std::atomic, I introduced a bug that
makes us miss the actual peak memory consumption, and only report the
second-highest memory usage in each zone.
This CL fixes that.

R=petermarshall@chromium.org

Bug: chromium:939724
Change-Id: I3db8eeb9719eb026cf6b4a9690c702cbc4c11bd9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1541227Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60505}

src/zone/accounting-allocator.cc

@@ -18,7 +18,7 @@ Segment* AccountingAllocator::AllocateSegment(size_t bytes) {
   if (memory == nullptr) return nullptr;
 
   size_t current =
-      current_memory_usage_.fetch_add(bytes, std::memory_order_relaxed);
+      current_memory_usage_.fetch_add(bytes, std::memory_order_relaxed) + bytes;
   size_t max = max_memory_usage_.load(std::memory_order_relaxed);
   while (current > max && !max_memory_usage_.compare_exchange_weak(
                               max, current, std::memory_order_relaxed)) {

test/cctest/test-allocation.cc

@@ -105,6 +105,34 @@ TEST(AccountingAllocatorOOM) {
   CHECK_EQ(result == nullptr, platform.oom_callback_called);
 }
 
+TEST(AccountingAllocatorCurrentAndMax) {
+  AllocationPlatform platform;
+  v8::internal::AccountingAllocator allocator;
+  static constexpr size_t kAllocationSizes[] = {51, 231, 27};
+  std::vector<v8::internal::Segment*> segments;
+  CHECK_EQ(0, allocator.GetCurrentMemoryUsage());
+  CHECK_EQ(0, allocator.GetMaxMemoryUsage());
+  size_t expected_current = 0;
+  size_t expected_max = 0;
+  for (size_t size : kAllocationSizes) {
+    segments.push_back(allocator.AllocateSegment(size));
+    CHECK_NOT_NULL(segments.back());
+    CHECK_EQ(size, segments.back()->total_size());
+    expected_current += size;
+    if (expected_current > expected_max) expected_max = expected_current;
+    CHECK_EQ(expected_current, allocator.GetCurrentMemoryUsage());
+    CHECK_EQ(expected_max, allocator.GetMaxMemoryUsage());
+  }
+  for (auto* segment : segments) {
+    expected_current -= segment->total_size();
+    allocator.ReturnSegment(segment);
+    CHECK_EQ(expected_current, allocator.GetCurrentMemoryUsage());
+  }
+  CHECK_EQ(expected_max, allocator.GetMaxMemoryUsage());
+  CHECK_EQ(0, allocator.GetCurrentMemoryUsage());
+  CHECK(!platform.oom_callback_called);
+}
+
 TEST(MallocedOperatorNewOOM) {
   AllocationPlatform platform;
   CHECK(!platform.oom_callback_called);