Use MADV_FREE_REUSABLE instead of MADV_FREE in partition alloc for macOS.

base/allocator/partition_allocator/page_allocator.cc

 // Copyright (c) 2013 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.
 
 #include "base/allocator/partition_allocator/page_allocator.h"
 
 #include <limits.h>
 
 #include <atomic>
 
@@ skipping 198 matching lines @@
 #if defined(OS_POSIX)
   return !mprotect(address, length, PROT_READ | PROT_WRITE);
 #else
   return !!VirtualAlloc(address, length, MEM_COMMIT, PAGE_READWRITE);
 #endif
 }
 
 void DecommitSystemPages(void* address, size_t length) {
   DCHECK(!(length & kSystemPageOffsetMask));
 #if defined(OS_POSIX)
+#if defined(OS_MACOSX)
+  // On macOS, MADV_FREE_REUSABLE has comparable behavior to MADV_FREE, but also
+  // marks the pages with the reusable bit, which allows both Activity Monitor
+  // and memory-infra to correctly track the pages.
+  int ret = madvise(address, length, MADV_FREE_REUSABLE);
+#else
   int ret = madvise(address, length, MADV_FREE);
+#endif
   if (ret != 0 && errno == EINVAL) {
     // MADV_FREE only works on Linux 4.5+ . If request failed,
     // retry with older MADV_DONTNEED . Note that MADV_FREE
     // being defined at compile time doesn't imply runtime support.
     ret = madvise(address, length, MADV_DONTNEED);
   }
   CHECK(!ret);
 #else
   SetSystemPagesInaccessible(address, length);
 #endif
@@ skipping 40 matching lines @@
     CHECK(ret);
   }
 #endif
 }
 
 uint32_t GetAllocPageErrorCode() {
   return s_allocPageErrorCode;
 }
 
 }  // namespace base