PCScan: Remove compile-time guard

These days PCScan and its bitmaps are lazily committed after startup.
Since bitmaps are not committed until PCScan is enabled, there is no
need for having a separate compile-time flag to avoid paying for used
memory.

Bug: 11297512
Change-Id: I9226a718be6309bc43de5f9f67e7c84e223eacbd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2539198
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Bartek Nowierski <bartekn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827925}

base/allocator/partition_allocator/partition_alloc_features.cc

@@ -20,12 +20,10 @@ const Feature kPartitionAllocGigaCage{"PartitionAllocGigaCage32bit",
                                       FEATURE_DISABLED_BY_DEFAULT};
 #endif
 
-#if ALLOW_ENABLING_PCSCAN
 // If enabled, PCScan is turned on by default for all partitions that don't
 // disable it explicitly.
 const Feature kPartitionAllocPCScan{"PartitionAllocPCScan",
                                     FEATURE_DISABLED_BY_DEFAULT};
-#endif
 
 }  // namespace features
 }  // namespace base

base/allocator/partition_allocator/partition_alloc_features.h

@@ -19,8 +19,6 @@
 #include <VersionHelpers.h>
 #endif
 
-#define ALLOW_ENABLING_PCSCAN 0
-
 namespace base {
 
 struct Feature;
@@ -63,9 +61,9 @@ ALWAYS_INLINE bool IsPartitionAllocGigaCageEnabled() {
 }
 
 ALWAYS_INLINE bool IsPartitionAllocPCScanEnabled() {
-#if !defined(PA_HAS_64_BITS_POINTERS) || !ALLOW_ENABLING_PCSCAN
+#if !defined(PA_HAS_64_BITS_POINTERS)
   return false;
-#endif
+#endif  // !PA_HAS_64_BITS_POINTERS
   // TODO(bikineev): Calling this function can allocate which can cause
   // reentrancy for the 'PA as malloc' configuration.
   return FeatureList::IsEnabled(kPartitionAllocPCScan);

base/allocator/partition_allocator/partition_root.cc

@@ -369,11 +369,7 @@ void PartitionRoot<thread_safe>::Init(PartitionOptions opts) {
   // the beginning of the slot.
   allow_extras = (opts.alignment != PartitionOptions::Alignment::kAlignedAlloc);
 
-#if ALLOW_ENABLING_PCSCAN
   scannable = (opts.pcscan != PartitionOptions::PCScan::kAlwaysDisabled);
-#else
-  scannable = false;
-#endif
   // Concurrent freeing in PCScan can only safely work on thread-safe
   // partitions.
   if (thread_safe &&

base/allocator/partition_allocator/pcscan_unittest.cc

@@ -9,8 +9,6 @@
 #include "base/allocator/partition_allocator/partition_alloc.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
-#if ALLOW_ENABLING_PCSCAN
-
 namespace base {
 namespace internal {
 
@@ -307,6 +305,4 @@ TEST_F(PCScanTest, DanglingInnerReference) {
 }  // namespace internal
 }  // namespace base
 
-#endif
-
 #endif  // defined(MEMORY_TOOL_REPLACES_ALLOCATOR)