--- old/src/share/vm/gc_implementation/parallelScavenge/generationSizer.cpp	2015-03-26 10:24:09.734936719 +0100
+++ new/src/share/vm/gc_implementation/parallelScavenge/generationSizer.cpp	2015-03-26 10:24:09.660934589 +0100
@@ -66,9 +66,10 @@
 
 void GenerationSizer::initialize_size_info() {
   trace_gen_sizes("ps heap raw");
-  const size_t page_sz = os::page_size_for_region(_min_heap_byte_size,
-                                                  _max_heap_byte_size,
-                                                  8);
+  const size_t max_page_sz = os::page_size_for_region(_max_heap_byte_size, 8);
+  const size_t min_pages = 4; // 1 for eden + 1 for each survivor + 1 for old
+  const size_t min_page_sz = os::page_size_for_region(_min_heap_byte_size, min_pages);
+  const size_t page_sz = MIN2(max_page_sz, min_page_sz);
 
   // Can a page size be something else than a power of two?
   assert(is_power_of_2((intptr_t)page_sz), "must be a power of 2");
--- old/src/share/vm/gc_implementation/parallelScavenge/parMarkBitMap.cpp	2015-03-26 10:24:10.231951025 +0100
+++ new/src/share/vm/gc_implementation/parallelScavenge/parMarkBitMap.cpp	2015-03-26 10:24:10.156948866 +0100
@@ -55,7 +55,7 @@
 
   const size_t words = bits / BitsPerWord;
   const size_t raw_bytes = words * sizeof(idx_t);
-  const size_t page_sz = os::page_size_for_region(raw_bytes, raw_bytes, 10);
+  const size_t page_sz = os::page_size_for_region(raw_bytes, 10);
   const size_t granularity = os::vm_allocation_granularity();
   _reserved_byte_size = align_size_up(raw_bytes, MAX2(page_sz, granularity));
 
--- old/src/share/vm/gc_implementation/parallelScavenge/psParallelCompact.cpp	2015-03-26 10:24:10.640962798 +0100
+++ new/src/share/vm/gc_implementation/parallelScavenge/psParallelCompact.cpp	2015-03-26 10:24:10.559960466 +0100
@@ -401,7 +401,7 @@
 ParallelCompactData::create_vspace(size_t count, size_t element_size)
 {
   const size_t raw_bytes = count * element_size;
-  const size_t page_sz = os::page_size_for_region(raw_bytes, raw_bytes, 10);
+  const size_t page_sz = os::page_size_for_region(raw_bytes, 10);
   const size_t granularity = os::vm_allocation_granularity();
   _reserved_byte_size = align_size_up(raw_bytes, MAX2(page_sz, granularity));
 
--- old/src/share/vm/memory/heap.cpp	2015-03-26 10:24:11.067975089 +0100
+++ new/src/share/vm/memory/heap.cpp	2015-03-26 10:24:10.997973074 +0100
@@ -97,9 +97,13 @@
   _log2_segment_size = exact_log2(segment_size);
 
   // Reserve and initialize space for _memory.
-  const size_t page_size = os::can_execute_large_page_memory() ?
-          os::page_size_for_region(committed_size, reserved_size, 8) :
-          os::vm_page_size();
+  size_t page_size = os::vm_page_size();
+  if (os::can_execute_large_page_memory()) {
+    const size_t min_pages = 8;
+    page_size = MIN2(os::page_size_for_region(committed_size, min_pages),
+                     os::page_size_for_region(reserved_size, min_pages));
+  }
+
   const size_t granularity = os::vm_allocation_granularity();
   const size_t r_align = MAX2(page_size, granularity);
   const size_t r_size = align_size_up(reserved_size, r_align);
--- old/src/share/vm/prims/jni.cpp	2015-03-26 10:24:11.465986546 +0100
+++ new/src/share/vm/prims/jni.cpp	2015-03-26 10:24:11.384984214 +0100
@@ -5071,6 +5071,7 @@
   unit_test_function_call
 
 // Forward declaration
+void TestOS_test();
 void TestReservedSpace_test();
 void TestReserveMemorySpecial_test();
 void TestVirtualSpace_test();
@@ -5092,6 +5093,7 @@
 void execute_internal_vm_tests() {
   if (ExecuteInternalVMTests) {
     tty->print_cr("Running internal VM tests");
+    run_unit_test(TestOS_test());
     run_unit_test(TestReservedSpace_test());
     run_unit_test(TestReserveMemorySpecial_test());
     run_unit_test(TestVirtualSpace_test());
--- old/src/share/vm/runtime/os.cpp	2015-03-26 10:24:11.931999959 +0100
+++ new/src/share/vm/runtime/os.cpp	2015-03-26 10:24:11.854997743 +0100
@@ -1315,24 +1315,15 @@
   return (sp > (stack_limit + reserved_area));
 }
 
-size_t os::page_size_for_region(size_t region_min_size, size_t region_max_size,
-                                uint min_pages)
-{
+size_t os::page_size_for_region(size_t region_size, size_t min_pages) {
   assert(min_pages > 0, "sanity");
   if (UseLargePages) {
-    const size_t max_page_size = region_max_size / min_pages;
-
-    for (unsigned int i = 0; _page_sizes[i] != 0; ++i) {
-      const size_t sz = _page_sizes[i];
-      const size_t mask = sz - 1;
-      if ((region_min_size & mask) == 0 && (region_max_size & mask) == 0) {
-        // The largest page size with no fragmentation.
-        return sz;
-      }
+    const size_t max_page_size = region_size / min_pages;
 
-      if (sz <= max_page_size) {
-        // The largest page size that satisfies the min_pages requirement.
-        return sz;
+    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)) {
+        return page_size;
       }
     }
   }
@@ -1574,3 +1565,63 @@
   return result;
 }
 #endif
+
+/////////////// Unit tests ///////////////
+
+#ifndef PRODUCT
+
+#define assert_eq(a,b) assert(a == b, err_msg(SIZE_FORMAT " != " SIZE_FORMAT, a, b))
+
+class TestOS : AllStatic {
+  static size_t small_page_size() {
+    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);
+  }
+
+  static void test_page_size_for_region() {
+    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);
+
+        assert_eq(page, small_page);
+      }
+    }
+  }
+
+  static void test_page_size_for_region_alignment() {
+    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);
+        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);
+        assert_eq(page, large_page);
+      }
+    }
+  }
+
+ public:
+  static void run_tests() {
+    test_page_size_for_region();
+    test_page_size_for_region_alignment();
+  }
+};
+
+void TestOS_test() {
+  TestOS::run_tests();
+}
+
+#endif // PRODUCT
--- old/src/share/vm/runtime/os.hpp	2015-03-26 10:24:15.922114811 +0100
+++ new/src/share/vm/runtime/os.hpp	2015-03-26 10:24:15.840112451 +0100
@@ -265,19 +265,11 @@
   // Return the default page size.
   static int    vm_page_size();
 
-  // Return the page size to use for a region of memory.  The min_pages argument
-  // is a hint intended to limit fragmentation; it says the returned page size
-  // should be <= region_max_size / min_pages.  Because min_pages is a hint,
-  // this routine may return a size larger than region_max_size / min_pages.
-  //
-  // The current implementation ignores min_pages if a larger page size is an
-  // exact multiple of both region_min_size and region_max_size.  This allows
-  // larger pages to be used when doing so would not cause fragmentation; in
-  // particular, a single page can be used when region_min_size ==
-  // region_max_size == a supported page size.
-  static size_t page_size_for_region(size_t region_min_size,
-                                     size_t region_max_size,
-                                     uint min_pages);
+  // Returns the page size to use for a region of memory.
+  // region_size / min_pages will always be greater than or equal to the
+  // returned value.
+  static size_t page_size_for_region(size_t region_size, size_t min_pages);
+
   // Return the largest page size that can be used
   static size_t max_page_size() {
     // The _page_sizes array is sorted in descending order.
--- old/src/share/vm/runtime/virtualspace.cpp	2015-03-26 10:24:16.368127649 +0100
+++ new/src/share/vm/runtime/virtualspace.cpp	2015-03-26 10:24:16.288125346 +0100
@@ -53,7 +53,7 @@
 }
 
 ReservedSpace::ReservedSpace(size_t size) {
-  size_t page_size = os::page_size_for_region(size, size, 1);
+  size_t page_size = os::page_size_for_region(size, 1);
   bool large_pages = page_size != (size_t)os::vm_page_size();
   // Don't force the alignment to be large page aligned,
   // since that will waste memory.
@@ -372,7 +372,7 @@
 
 
 bool VirtualSpace::initialize(ReservedSpace rs, size_t committed_size) {
-  const size_t max_commit_granularity = os::page_size_for_region(rs.size(), rs.size(), 1);
+  const size_t max_commit_granularity = os::page_size_for_region(rs.size(), 1);
   return initialize_with_granularity(rs, committed_size, max_commit_granularity);
 }
 
@@ -995,7 +995,7 @@
     case Disable:
       return vs.initialize_with_granularity(rs, 0, os::vm_page_size());
     case Commit:
-      return vs.initialize_with_granularity(rs, 0, os::page_size_for_region(rs.size(), rs.size(), 1));
+      return vs.initialize_with_granularity(rs, 0, os::page_size_for_region(rs.size(), 1));
     }
   }