PartitionAlloc: PCScan: Perform scan only when quarantine is not empty.

Bug: 11297512
Change-Id: I7bf329df83e8ae0185578cc0bf1b68090a937b4e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2547323Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828955}

base/allocator/partition_allocator/partition_root.cc

@@ -610,7 +610,7 @@ template <bool thread_safe>
 void PartitionRoot<thread_safe>::PurgeMemory(int flags) {
   // TODO(chromium:1129751): Change to LIKELY once PCScan is enabled by default.
   if (UNLIKELY(pcscan)) {
-    pcscan->PerformScan(
+    pcscan->PerformScanIfNeeded(
         internal::PCScan<thread_safe>::InvocationMode::kBlocking);
   }
 

base/allocator/partition_allocator/pcscan.cc

@@ -484,6 +484,13 @@ void PCScan<thread_safe>::PerformScan(InvocationMode invocation_mode) {
   }
 }
 
+template <bool thread_safe>
+void PCScan<thread_safe>::PerformScanIfNeeded(InvocationMode invocation_mode) {
+  // Perform PCScan only if quarantine is not empty.
+  if (quarantine_data_.size())
+    PerformScan(invocation_mode);
+}
+
 template class PCScan<ThreadSafe>;
 template class PCScan<NotThreadSafe>;
 

base/allocator/partition_allocator/pcscan.h

@@ -53,7 +53,7 @@ class BASE_EXPORT PCScan final {
 
   ALWAYS_INLINE void MoveToQuarantine(void* ptr, SlotSpan* slot_span);
 
-  void PerformScan(InvocationMode invocation_mode);
+  void PerformScanIfNeeded(InvocationMode invocation_mode);
 
  private:
   class PCScanTask;
@@ -82,6 +82,8 @@ class BASE_EXPORT PCScan final {
     size_t last_size_ = 0;
   };
 
+  void PerformScan(InvocationMode invocation_mode);
+
   Root* root_;
   QuarantineData quarantine_data_;
   std::atomic<bool> in_progress_{false};