AIX: [Memory] Use madvise on POSIX to allow OS to reclaim memory.

Port 2cbfa244

Original Commit Message:

  [Memory] Use madvise on POSIX to allow OS to reclaim memory.

  - Use madvise when setting no permissions on memory.
  - Move platform specific mmap flag calculations to a helper fn.

  Bug: chromium:756050,chromium:788341
  Change-Id: I7d420a0abee9656a57fb0317301322da2fd7d7b5
  Reviewed-on: https://chromium-review.googlesource.com/790932


Change-Id: I5f7957066d0be96bd429b3d55c9293ffb996750c
Reviewed-on: https://chromium-review.googlesource.com/804554Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49961}

src/base/platform/platform-posix.cc

@@ -137,6 +137,8 @@ int ReclaimInaccessibleMemory(void* address, size_t size) {
   // marks the pages with the reusable bit, which allows both Activity Monitor
   // and memory-infra to correctly track the pages.
   int ret = madvise(address, size, MADV_FREE_REUSABLE);
+#elif defined(_AIX)
+  int ret = madvise(reinterpret_cast<caddr_t>(address), size, MADV_FREE);
 #else
   int ret = madvise(address, size, MADV_FREE);
 #endif
@@ -144,7 +146,11 @@ int ReclaimInaccessibleMemory(void* address, size_t size) {
     // 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.
+#if defined(_AIX)
+    ret = madvise(reinterpret_cast<caddr_t>(address), size, MADV_DONTNEED);
+#else
     ret = madvise(address, size, MADV_DONTNEED);
+#endif
   }
   return ret;
 }