Use sysctlbyname() to get kernel page size.

base/trace_event/process_memory_dump.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_TRACE_EVENT_PROCESS_MEMORY_DUMP_H_
 #define BASE_TRACE_EVENT_PROCESS_MEMORY_DUMP_H_
 
 #include <stddef.h>
 
 #include <unordered_map>
 #include <vector>
 
 #include "base/base_export.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_vector.h"
 #include "base/trace_event/memory_allocator_dump.h"
 #include "base/trace_event/memory_allocator_dump_guid.h"
 #include "base/trace_event/memory_dump_session_state.h"
 #include "base/trace_event/process_memory_maps.h"
 #include "base/trace_event/process_memory_totals.h"
 #include "build/build_config.h"
 
 // Define COUNT_RESIDENT_BYTES_SUPPORTED if platform supports counting of the
 // resident memory.
-// TODO(crbug.com/542671): COUNT_RESIDENT_BYTES_SUPPORTED is disabled on iOS
-// as it cause memory corruption on iOS 9.0+ devices.
-#if (defined(OS_POSIX) && !defined(OS_NACL) && !defined(OS_IOS)) || \
-    defined(OS_WIN)
+#if (defined(OS_POSIX) && !defined(OS_NACL)) || defined(OS_WIN)
 #define COUNT_RESIDENT_BYTES_SUPPORTED
 #endif
 
 namespace base {
 namespace trace_event {
 
 class MemoryDumpManager;
 class MemoryDumpSessionState;
 class TracedValue;
 
 // ProcessMemoryDump is as a strongly typed container which holds the dumps
 // produced by the MemoryDumpProvider(s) for a specific process.
 class BASE_EXPORT ProcessMemoryDump {
  public:
   struct MemoryAllocatorDumpEdge {
     MemoryAllocatorDumpGuid source;
     MemoryAllocatorDumpGuid target;
     int importance;
     const char* type;
   };
 
   // Maps allocator dumps absolute names (allocator_name/heap/subheap) to
   // MemoryAllocatorDump instances.
   using AllocatorDumpsMap =
       std::unordered_map<std::string, scoped_ptr<MemoryAllocatorDump>>;
 
   using HeapDumpsMap = std::unordered_map<std::string, scoped_ptr<TracedValue>>;
 
 #if defined(COUNT_RESIDENT_BYTES_SUPPORTED)
+  // Returns the number of bytes in a kernel memory page. Some platforms may
+  // have a different value for kernel page sizes from user page sizes. It is
+  // important to use kernel memory page sizes for resident bytes calculation.
+  // In most cases, the two are the same.
+  static size_t GetSystemPageSize();
+
   // Returns the total bytes resident for a virtual address range, with given
   // |start_address| and |mapped_size|. |mapped_size| is specified in bytes. The
   // value returned is valid only if the given range is currently mmapped by the
   // process. The |start_address| must be page-aligned.
   static size_t CountResidentBytes(void* start_address, size_t mapped_size);
 #endif
 
   ProcessMemoryDump(const scoped_refptr<MemoryDumpSessionState>& session_state);
   ~ProcessMemoryDump();
 
@@ skipping 120 matching lines @@
   // Keeps track of relationships between MemoryAllocatorDump(s).
   std::vector<MemoryAllocatorDumpEdge> allocator_dumps_edges_;
 
   DISALLOW_COPY_AND_ASSIGN(ProcessMemoryDump);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_PROCESS_MEMORY_DUMP_H_