Solaris/OpenBSD/FreeBSD: [heap] Uncommit unused large object page memory.

Port d61a5c37

Original commit message:

    As a first step I uncommit the memory on the main thread. Also
    to measure impact and stability of that optimization. In a
    follow-up CL, the uncommitting should be moved on the concurrent thread.

R=jochen@chromium.org, hpayer@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2245703002
Cr-Commit-Position: refs/heads/master@{#38654}

AUTHORS

@@ -89,6 +89,7 @@ Matthew Sporleder <msporleder@gmail.com>
 Maxim Mossienko <maxim.mossienko@gmail.com>
 Michael Lutz <michi@icosahedron.de>
 Michael Smith <mike@w3.org>
+Michaël Zasso <mic.besace@gmail.com>
 Mike Gilbert <floppymaster@gmail.com>
 Mike Pennisi <mike@mikepennisi.com>
 Milton Chiang <milton.chiang@mediatek.com>

src/base/platform/platform-freebsd.cc

@@ -246,6 +246,10 @@ bool VirtualMemory::UncommitRegion(void* base, size_t size) {
               kMmapFdOffset) != MAP_FAILED;
 }
 
+bool VirtualMemory::ReleasePartialRegion(void* base, size_t size,
+                                         void* free_start, size_t free_size) {
+  return munmap(free_start, free_size) == 0;
+}
 
 bool VirtualMemory::ReleaseRegion(void* base, size_t size) {
   return munmap(base, size) == 0;

src/base/platform/platform-openbsd.cc

@@ -277,6 +277,10 @@ bool VirtualMemory::UncommitRegion(void* base, size_t size) {
               kMmapFdOffset) != MAP_FAILED;
 }
 
+bool VirtualMemory::ReleasePartialRegion(void* base, size_t size,
+                                         void* free_start, size_t free_size) {
+  return munmap(free_start, free_size) == 0;
+}
 
 bool VirtualMemory::ReleaseRegion(void* base, size_t size) {
   return munmap(base, size) == 0;

src/base/platform/platform-solaris.cc

@@ -198,6 +198,10 @@ bool VirtualMemory::UncommitRegion(void* base, size_t size) {
               kMmapFdOffset) != MAP_FAILED;
 }
 
+bool VirtualMemory::ReleasePartialRegion(void* base, size_t size,
+                                         void* free_start, size_t free_size) {
+  return munmap(free_start, free_size) == 0;
+}
 
 bool VirtualMemory::ReleaseRegion(void* base, size_t size) {
   return munmap(base, size) == 0;