chromeos_hugepage: mlock in the area covered by huge pages

We are putting our most used text into a region that can be backed by
huge pages, however we can lose those pages when we encounter memory
pressure, so we should be locking them into place to avoid that.

R=llozano@chromium.org

Bug: 913700
Change-Id: If9ae32ae046a21d5bf7af4e43624323b3429d9f8
Reviewed-on: https://chromium-review.googlesource.com/c/1371206Reviewed-by: George Burgess <gbiv@chromium.org>
Commit-Queue: Sonny Rao <sonnyrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615724}

chromeos/hugepage_text/hugepage_text.cc

@@ -9,6 +9,8 @@
 
 #include <link.h>
 #include <sys/mman.h>
+#include <sys/resource.h>
+#include <sys/time.h>
 
 #include "base/bit_cast.h"
 #include "base/logging.h"
@@ -61,6 +63,10 @@ static void* GetTransparentHugepageMapping(const size_t hsize) {
     munmap(haddr, hsize);
     return NULL;
   }
+
+  if (mlock(haddr, hsize)) {
+    PLOG(INFO) << "Mlocking text pages failed";
+  }
   return haddr;
 }