src/share/vm/runtime/os.cpp

rev 7180 : 8067469: G1 ignores AlwaysPreTouch
Summary: Factor out pretouch code of the various virtual space management classes and use them everywhere including in G1.
Reviewed-by: stefank, ehelin, dholmes
rev 7181 : 8049864: TestParallelHeapSizeFlags fails with unexpected heap size
Reviewed-by: sjohanss, jmasa
rev 7183 : 8066875: VirtualSpace does not use large pages
Reviewed-by: stefank, tschatzl, anoll, thartmann

@@ -1313,26 +1313,36 @@
   // The very lower end of the stack
   address stack_limit = thread->stack_base() - thread->stack_size();
   return (sp > (stack_limit + reserved_area));
 }
 
-size_t os::page_size_for_region(size_t region_size, size_t min_pages) {
+size_t os::page_size_for_region(size_t region_size, size_t min_pages, bool must_be_aligned) {
   assert(min_pages > 0, "sanity");
   if (UseLargePages) {
     const size_t max_page_size = region_size / min_pages;
 
     for (size_t i = 0; _page_sizes[i] != 0; ++i) {
       const size_t page_size = _page_sizes[i];
-      if (page_size <= max_page_size && is_size_aligned(region_size, page_size)) {
+      if (page_size <= max_page_size) {
+        if (!must_be_aligned || is_size_aligned(region_size, page_size)) {
         return page_size;
       }
     }
   }
+  }
 
   return vm_page_size();
 }
 
+size_t os::page_size_for_region_aligned(size_t region_size, size_t min_pages) {
+  return page_size_for_region(region_size, min_pages, true);
+}
+
+size_t os::page_size_for_region_unaligned(size_t region_size, size_t min_pages) {
+  return page_size_for_region(region_size, min_pages, false);
+}
+
 #ifndef PRODUCT
 void os::trace_page_sizes(const char* str, const size_t* page_sizes, int count)
 {
   if (TracePageSizes) {
     tty->print("%s: ", str);

@@ -1577,21 +1587,21 @@
     return os::vm_page_size();
   }
 
   static size_t large_page_size() {
     const size_t large_page_size_example = 4 * M;
-    return os::page_size_for_region(large_page_size_example, 1);
+    return os::page_size_for_region_aligned(large_page_size_example, 1);
   }
 
-  static void test_page_size_for_region() {
+  static void test_page_size_for_region_aligned() {
     if (UseLargePages) {
       const size_t small_page = small_page_size();
       const size_t large_page = large_page_size();
 
       if (large_page > small_page) {
         size_t num_small_pages_in_large = large_page / small_page;
-        size_t page = os::page_size_for_region(large_page, num_small_pages_in_large);
+        size_t page = os::page_size_for_region_aligned(large_page, num_small_pages_in_large);
 
         assert_eq(page, small_page);
       }
     }
   }

@@ -1600,25 +1610,57 @@
     if (UseLargePages) {
       const size_t small_page = small_page_size();
       const size_t large_page = large_page_size();
       if (large_page > small_page) {
         const size_t unaligned_region = large_page + 17;
-        size_t page = os::page_size_for_region(unaligned_region, 1);
+        size_t page = os::page_size_for_region_aligned(unaligned_region, 1);
         assert_eq(page, small_page);
 
         const size_t num_pages = 5;
         const size_t aligned_region = large_page * num_pages;
-        page = os::page_size_for_region(aligned_region, num_pages);
+        page = os::page_size_for_region_aligned(aligned_region, num_pages);
         assert_eq(page, large_page);
       }
     }
   }
 
+  static void test_page_size_for_region_unaligned() {
+    if (UseLargePages) {
+      // Given exact page size, should return that page size.
+      for (size_t i = 0; os::_page_sizes[i] != 0; i++) {
+        size_t expected = os::_page_sizes[i];
+        size_t actual = os::page_size_for_region_unaligned(expected, 1);
+        assert_eq(expected, actual);
+      }
+
+      // Given slightly larger size than a page size, return the page size.
+      for (size_t i = 0; os::_page_sizes[i] != 0; i++) {
+        size_t expected = os::_page_sizes[i];
+        size_t actual = os::page_size_for_region_unaligned(expected + 17, 1);
+        assert_eq(expected, actual);
+      }
+
+      // Given a slightly smaller size than a page size,
+      // return the next smaller page size.
+      if (os::_page_sizes[1] > os::_page_sizes[0]) {
+        size_t expected = os::_page_sizes[0];
+        size_t actual = os::page_size_for_region_unaligned(os::_page_sizes[1] - 17, 1);
+        assert_eq(actual, expected);
+      }
+
+      // Return small page size for values less than a small page.
+      size_t small_page = small_page_size();
+      size_t actual = os::page_size_for_region_unaligned(small_page - 17, 1);
+      assert_eq(small_page, actual);
+    }
+  }
+
  public:
   static void run_tests() {
-    test_page_size_for_region();
+    test_page_size_for_region_aligned();
     test_page_size_for_region_alignment();
+    test_page_size_for_region_unaligned();
   }
 };
 
 void TestOS_test() {
   TestOS::run_tests();