7040485: Use transparent huge page on linux by default

Summary: Turn on UseLargePages by default but try only HugeTLBFS method if it is not explicitly specified on the command line.
Reviewed-by: ysr

src/os/linux/vm/globals_linux.hpp

 /*
- * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2005, 2011, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -47,7 +47,7 @@
 // Defines Linux-specific default values. The flags are available on all
 // platforms, but they may have different default values on other platforms.
 //
-define_pd_global(bool, UseLargePages, false);
+define_pd_global(bool, UseLargePages, true);
 define_pd_global(bool, UseLargePagesIndividualAllocation, false);
 define_pd_global(bool, UseOSErrorReporting, false);
 define_pd_global(bool, UseThreadPriorities, true) ;

src/os/linux/vm/os_linux.cpp

@@ -2914,16 +2914,21 @@ static void set_coredump_filter(void) {
 
 static size_t _large_page_size = 0;
 
-bool os::large_page_init() {
+void os::large_page_init() {
   if (!UseLargePages) {
     UseHugeTLBFS = false;
     UseSHM = false;
-    return false;
+    return;
   }
 
   if (FLAG_IS_DEFAULT(UseHugeTLBFS) && FLAG_IS_DEFAULT(UseSHM)) {
-    // Our user has not expressed a preference, so we'll try both.
-    UseHugeTLBFS = UseSHM = true;
+    // If UseLargePages is specified on the command line try both methods,
+    // if it's default, then try only HugeTLBFS.
+    if (FLAG_IS_DEFAULT(UseLargePages)) {
+      UseHugeTLBFS = true;
+    } else {
+      UseHugeTLBFS = UseSHM = true;
+    }
   }
 
   if (LargePageSizeInBytes) {
@@ -2978,7 +2983,6 @@ bool os::large_page_init() {
     _page_sizes[1] = default_page_size;
     _page_sizes[2] = 0;
   }
-
   UseHugeTLBFS = UseHugeTLBFS &&
                  Linux::hugetlbfs_sanity_check(warn_on_failure, _large_page_size);
 
@@ -2988,12 +2992,6 @@ bool os::large_page_init() {
   UseLargePages = UseHugeTLBFS || UseSHM;
 
   set_coredump_filter();
-
-  // Large page support is available on 2.6 or newer kernel, some vendors
-  // (e.g. Redhat) have backported it to their 2.4 based distributions.
-  // We optimistically assume the support is available. If later it turns out
-  // not true, VM will automatically switch to use regular page size.
-  return true;
 }
 
 #ifndef SHM_HUGETLB
@@ -4118,7 +4116,7 @@ jint os::init_2(void)
 #endif
   }
 
-  FLAG_SET_DEFAULT(UseLargePages, os::large_page_init());
+  os::large_page_init();
 
   // initialize suspend/resume support - must do this before signal_sets_init()
   if (SR_initialize() != 0) {

src/os/solaris/vm/os_solaris.cpp

@@ -3336,11 +3336,11 @@ bool os::Solaris::mpss_sanity_check(bool warn, size_t * page_size) {
   return true;
 }
 
-bool os::large_page_init() {
+void os::large_page_init() {
   if (!UseLargePages) {
     UseISM = false;
     UseMPSS = false;
-    return false;
+    return;
   }
 
   // print a warning if any large page related flag is specified on command line
@@ -3361,7 +3361,6 @@ bool os::large_page_init() {
             Solaris::mpss_sanity_check(warn_on_failure, &_large_page_size);
 
   UseLargePages = UseISM || UseMPSS;
-  return UseLargePages;
 }
 
 bool os::Solaris::set_mpss_range(caddr_t start, size_t bytes, size_t align) {
@@ -4992,7 +4991,7 @@ jint os::init_2(void) {
 #endif
 }
 
-  FLAG_SET_DEFAULT(UseLargePages, os::large_page_init());
+  os::large_page_init();
 
   // Check minimum allowable stack size for thread creation and to initialize
   // the java system classes, including StackOverflowError - depends on page

src/os/windows/vm/os_windows.cpp

@@ -2762,8 +2762,8 @@ static void cleanup_after_large_page_init() {
   _hToken = NULL;
 }
 
-bool os::large_page_init() {
-  if (!UseLargePages) return false;
+void os::large_page_init() {
+  if (!UseLargePages) return;
 
   // print a warning if any large page related flag is specified on command line
   bool warn_on_failure = !FLAG_IS_DEFAULT(UseLargePages) ||
@@ -2808,7 +2808,7 @@ bool os::large_page_init() {
   }
 
   cleanup_after_large_page_init();
-  return success;
+  UseLargePages = success;
 }
 
 // On win32, one cannot release just a part of reserved memory, it's an
@@ -3561,7 +3561,7 @@ jint os::init_2(void) {
 #endif
 }
 
-  FLAG_SET_DEFAULT(UseLargePages, os::large_page_init());
+  os::large_page_init();
 
   // Setup Windows Exceptions
 

src/share/vm/runtime/os.hpp

@@ -274,7 +274,7 @@ class os: AllStatic {
   static char*  reserve_memory_special(size_t size, char* addr = NULL,
                 bool executable = false);
   static bool   release_memory_special(char* addr, size_t bytes);
-  static bool   large_page_init();
+  static void   large_page_init();
   static size_t large_page_size();
   static bool   can_commit_large_page_memory();
   static bool   can_execute_large_page_memory();