--- a/hotspot/src/share/vm/gc/g1/g1OopClosures.inline.hpp	Tue Apr 05 09:05:19 2016 +0200
+++ b/hotspot/src/share/vm/gc/g1/g1OopClosures.inline.hpp	Tue Apr 05 11:22:20 2016 +0200
@@ -176,13 +176,22 @@
 #endif // ASSERT
 
   assert(_from != NULL, "from region must be non-NULL");
-  assert(_from->is_in_reserved(p), "p is not in from");
+  assert(_from->is_in_reserved(p) ||
+         (_from->is_humongous() &&
+          _g1->heap_region_containing(p)->is_humongous() &&
+          _from->humongous_start_region() == _g1->heap_region_containing(p)->humongous_start_region()),
+         "p " PTR_FORMAT " is not in the same region %u or part of the correct humongous object starting at region %u.",
+         p2i(p), _from->hrm_index(), _from->humongous_start_region()->hrm_index());
 
   HeapRegion* to = _g1->heap_region_containing(obj);
   if (_from == to) {
     // Normally this closure should only be called with cross-region references.
     // But since Java threads are manipulating the references concurrently and we
     // reload the values things may have changed.
+    // Also this check lets slip through references from a humongous continues region
+    // to its humongous start region, as they are in different regions, and adds a
+    // remembered set entry. This is benign (apart from memory usage), as we never
+    // try to either evacuate or eager reclaim these kind of regions.
     return;
   }
 

--- a/hotspot/test/TEST.groups	Tue Apr 05 09:05:19 2016 +0200
+++ b/hotspot/test/TEST.groups	Tue Apr 05 11:22:20 2016 +0200
@@ -249,6 +249,7 @@
 #
 needs_g1gc = \
   compiler/regalloc/C1ObjectSpillInLogicOp.java \
+  gc/TestHumongousReferenceObject.java \
   gc/TestSmallHeap.java \
   gc/TestSystemGC.java \
   gc/arguments/TestAlignmentToUseLargePages.java \

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/test/gc/TestHumongousReferenceObject.java	Tue Apr 05 11:22:20 2016 +0200
@@ -0,0 +1,354 @@
+/*
+ * Copyright (c) 2016, 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
+ * under the terms of the GNU General License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+import jdk.internal.vm.annotation.Contended;
+
+/*
+ * @test
+ * @summary Test that verifies that iteration over large, plain Java objects, that potentially cross region boundaries on G1, with references in them works.
+ * @requires vm.gc == "null"
+ * @bug 8151499
+ * @modules java.base/jdk.internal.vm.annotation
+ * @run main/othervm -XX:+EnableContended -XX:-RestrictContended -Xmx1g -XX:+UseParallelGC -XX:ContendedPaddingWidth=8192 TestHumongousReferenceObject
+ * @run main/othervm -XX:+EnableContended -XX:-RestrictContended -Xmx1g -XX:+UseG1GC -XX:G1HeapRegionSize=1M -XX:ContendedPaddingWidth=8192 TestHumongousReferenceObject
+ * @run main/othervm -XX:+EnableContended -XX:-RestrictContended -Xmx1g -XX:+UseG1GC -XX:G1HeapRegionSize=2M -XX:ContendedPaddingWidth=8192 TestHumongousReferenceObject
+ * @run main/othervm -XX:+EnableContended -XX:-RestrictContended -Xmx1g -XX:+UseG1GC -XX:G1HeapRegionSize=4M -XX:ContendedPaddingWidth=8192 TestHumongousReferenceObject
+ * @run main/othervm -XX:+EnableContended -XX:-RestrictContended -Xmx1g -XX:+UseG1GC -XX:G1HeapRegionSize=8M -XX:ContendedPaddingWidth=8192 TestHumongousReferenceObject
+ */
+public class TestHumongousReferenceObject {
+
+    /*
+      Due to 300 fields with 8K @Contended padding around each field, it takes 2.4M bytes per instance.
+      With small G1 regions, it is bound to cross regions. G1 should properly (card) mark the object nevertheless.
+      With 1G heap, it is enough to allocate ~400 of these objects to provoke at least one GC.
+     */
+
+    static volatile Object instance;
+
+    public static void main(String[] args) {
+        for (int c = 0; c < 400; c++) {
+            instance = new TestHumongousReferenceObject();
+        }
+    }
+
+    @Contended Integer int_1 = new Integer(1);
+    @Contended Integer int_2 = new Integer(2);
+    @Contended Integer int_3 = new Integer(3);
+    @Contended Integer int_4 = new Integer(4);
+    @Contended Integer int_5 = new Integer(5);
+    @Contended Integer int_6 = new Integer(6);
+    @Contended Integer int_7 = new Integer(7);
+    @Contended Integer int_8 = new Integer(8);
+    @Contended Integer int_9 = new Integer(9);
+    @Contended Integer int_10 = new Integer(10);
+    @Contended Integer int_11 = new Integer(11);
+    @Contended Integer int_12 = new Integer(12);
+    @Contended Integer int_13 = new Integer(13);
+    @Contended Integer int_14 = new Integer(14);
+    @Contended Integer int_15 = new Integer(15);
+    @Contended Integer int_16 = new Integer(16);
+    @Contended Integer int_17 = new Integer(17);
+    @Contended Integer int_18 = new Integer(18);
+    @Contended Integer int_19 = new Integer(19);
+    @Contended Integer int_20 = new Integer(20);
+    @Contended Integer int_21 = new Integer(21);
+    @Contended Integer int_22 = new Integer(22);
+    @Contended Integer int_23 = new Integer(23);
+    @Contended Integer int_24 = new Integer(24);
+    @Contended Integer int_25 = new Integer(25);
+    @Contended Integer int_26 = new Integer(26);
+    @Contended Integer int_27 = new Integer(27);
+    @Contended Integer int_28 = new Integer(28);
+    @Contended Integer int_29 = new Integer(29);
+    @Contended Integer int_30 = new Integer(30);
+    @Contended Integer int_31 = new Integer(31);
+    @Contended Integer int_32 = new Integer(32);
+    @Contended Integer int_33 = new Integer(33);
+    @Contended Integer int_34 = new Integer(34);
+    @Contended Integer int_35 = new Integer(35);
+    @Contended Integer int_36 = new Integer(36);
+    @Contended Integer int_37 = new Integer(37);
+    @Contended Integer int_38 = new Integer(38);
+    @Contended Integer int_39 = new Integer(39);
+    @Contended Integer int_40 = new Integer(40);
+    @Contended Integer int_41 = new Integer(41);
+    @Contended Integer int_42 = new Integer(42);
+    @Contended Integer int_43 = new Integer(43);
+    @Contended Integer int_44 = new Integer(44);
+    @Contended Integer int_45 = new Integer(45);
+    @Contended Integer int_46 = new Integer(46);
+    @Contended Integer int_47 = new Integer(47);
+    @Contended Integer int_48 = new Integer(48);
+    @Contended Integer int_49 = new Integer(49);
+    @Contended Integer int_50 = new Integer(50);
+    @Contended Integer int_51 = new Integer(51);
+    @Contended Integer int_52 = new Integer(52);
+    @Contended Integer int_53 = new Integer(53);
+    @Contended Integer int_54 = new Integer(54);
+    @Contended Integer int_55 = new Integer(55);
+    @Contended Integer int_56 = new Integer(56);
+    @Contended Integer int_57 = new Integer(57);
+    @Contended Integer int_58 = new Integer(58);
+    @Contended Integer int_59 = new Integer(59);
+    @Contended Integer int_60 = new Integer(60);
+    @Contended Integer int_61 = new Integer(61);
+    @Contended Integer int_62 = new Integer(62);
+    @Contended Integer int_63 = new Integer(63);
+    @Contended Integer int_64 = new Integer(64);
+    @Contended Integer int_65 = new Integer(65);
+    @Contended Integer int_66 = new Integer(66);
+    @Contended Integer int_67 = new Integer(67);
+    @Contended Integer int_68 = new Integer(68);
+    @Contended Integer int_69 = new Integer(69);
+    @Contended Integer int_70 = new Integer(70);
+    @Contended Integer int_71 = new Integer(71);
+    @Contended Integer int_72 = new Integer(72);
+    @Contended Integer int_73 = new Integer(73);
+    @Contended Integer int_74 = new Integer(74);
+    @Contended Integer int_75 = new Integer(75);
+    @Contended Integer int_76 = new Integer(76);
+    @Contended Integer int_77 = new Integer(77);
+    @Contended Integer int_78 = new Integer(78);
+    @Contended Integer int_79 = new Integer(79);
+    @Contended Integer int_80 = new Integer(80);
+    @Contended Integer int_81 = new Integer(81);
+    @Contended Integer int_82 = new Integer(82);
+    @Contended Integer int_83 = new Integer(83);
+    @Contended Integer int_84 = new Integer(84);
+    @Contended Integer int_85 = new Integer(85);
+    @Contended Integer int_86 = new Integer(86);
+    @Contended Integer int_87 = new Integer(87);
+    @Contended Integer int_88 = new Integer(88);
+    @Contended Integer int_89 = new Integer(89);
+    @Contended Integer int_90 = new Integer(90);
+    @Contended Integer int_91 = new Integer(91);
+    @Contended Integer int_92 = new Integer(92);
+    @Contended Integer int_93 = new Integer(93);
+    @Contended Integer int_94 = new Integer(94);
+    @Contended Integer int_95 = new Integer(95);
+    @Contended Integer int_96 = new Integer(96);
+    @Contended Integer int_97 = new Integer(97);
+    @Contended Integer int_98 = new Integer(98);
+    @Contended Integer int_99 = new Integer(99);
+    @Contended Integer int_100 = new Integer(100);
+    @Contended Integer int_101 = new Integer(101);
+    @Contended Integer int_102 = new Integer(102);
+    @Contended Integer int_103 = new Integer(103);
+    @Contended Integer int_104 = new Integer(104);
+    @Contended Integer int_105 = new Integer(105);
+    @Contended Integer int_106 = new Integer(106);
+    @Contended Integer int_107 = new Integer(107);
+    @Contended Integer int_108 = new Integer(108);
+    @Contended Integer int_109 = new Integer(109);
+    @Contended Integer int_110 = new Integer(110);
+    @Contended Integer int_111 = new Integer(111);
+    @Contended Integer int_112 = new Integer(112);
+    @Contended Integer int_113 = new Integer(113);
+    @Contended Integer int_114 = new Integer(114);
+    @Contended Integer int_115 = new Integer(115);
+    @Contended Integer int_116 = new Integer(116);
+    @Contended Integer int_117 = new Integer(117);
+    @Contended Integer int_118 = new Integer(118);
+    @Contended Integer int_119 = new Integer(119);
+    @Contended Integer int_120 = new Integer(120);
+    @Contended Integer int_121 = new Integer(121);
+    @Contended Integer int_122 = new Integer(122);
+    @Contended Integer int_123 = new Integer(123);
+    @Contended Integer int_124 = new Integer(124);
+    @Contended Integer int_125 = new Integer(125);
+    @Contended Integer int_126 = new Integer(126);
+    @Contended Integer int_127 = new Integer(127);
+    @Contended Integer int_128 = new Integer(128);
+    @Contended Integer int_129 = new Integer(129);
+    @Contended Integer int_130 = new Integer(130);
+    @Contended Integer int_131 = new Integer(131);
+    @Contended Integer int_132 = new Integer(132);
+    @Contended Integer int_133 = new Integer(133);
+    @Contended Integer int_134 = new Integer(134);
+    @Contended Integer int_135 = new Integer(135);
+    @Contended Integer int_136 = new Integer(136);
+    @Contended Integer int_137 = new Integer(137);
+    @Contended Integer int_138 = new Integer(138);
+    @Contended Integer int_139 = new Integer(139);
+    @Contended Integer int_140 = new Integer(140);
+    @Contended Integer int_141 = new Integer(141);
+    @Contended Integer int_142 = new Integer(142);
+    @Contended Integer int_143 = new Integer(143);
+    @Contended Integer int_144 = new Integer(144);
+    @Contended Integer int_145 = new Integer(145);
+    @Contended Integer int_146 = new Integer(146);
+    @Contended Integer int_147 = new Integer(147);
+    @Contended Integer int_148 = new Integer(148);
+    @Contended Integer int_149 = new Integer(149);
+    @Contended Integer int_150 = new Integer(150);
+    @Contended Integer int_151 = new Integer(151);
+    @Contended Integer int_152 = new Integer(152);
+    @Contended Integer int_153 = new Integer(153);
+    @Contended Integer int_154 = new Integer(154);
+    @Contended Integer int_155 = new Integer(155);
+    @Contended Integer int_156 = new Integer(156);
+    @Contended Integer int_157 = new Integer(157);
+    @Contended Integer int_158 = new Integer(158);
+    @Contended Integer int_159 = new Integer(159);
+    @Contended Integer int_160 = new Integer(160);
+    @Contended Integer int_161 = new Integer(161);
+    @Contended Integer int_162 = new Integer(162);
+    @Contended Integer int_163 = new Integer(163);
+    @Contended Integer int_164 = new Integer(164);
+    @Contended Integer int_165 = new Integer(165);
+    @Contended Integer int_166 = new Integer(166);
+    @Contended Integer int_167 = new Integer(167);
+    @Contended Integer int_168 = new Integer(168);
+    @Contended Integer int_169 = new Integer(169);
+    @Contended Integer int_170 = new Integer(170);
+    @Contended Integer int_171 = new Integer(171);
+    @Contended Integer int_172 = new Integer(172);
+    @Contended Integer int_173 = new Integer(173);
+    @Contended Integer int_174 = new Integer(174);
+    @Contended Integer int_175 = new Integer(175);
+    @Contended Integer int_176 = new Integer(176);
+    @Contended Integer int_177 = new Integer(177);
+    @Contended Integer int_178 = new Integer(178);
+    @Contended Integer int_179 = new Integer(179);
+    @Contended Integer int_180 = new Integer(180);
+    @Contended Integer int_181 = new Integer(181);
+    @Contended Integer int_182 = new Integer(182);
+    @Contended Integer int_183 = new Integer(183);
+    @Contended Integer int_184 = new Integer(184);
+    @Contended Integer int_185 = new Integer(185);
+    @Contended Integer int_186 = new Integer(186);
+    @Contended Integer int_187 = new Integer(187);
+    @Contended Integer int_188 = new Integer(188);
+    @Contended Integer int_189 = new Integer(189);
+    @Contended Integer int_190 = new Integer(190);
+    @Contended Integer int_191 = new Integer(191);
+    @Contended Integer int_192 = new Integer(192);
+    @Contended Integer int_193 = new Integer(193);
+    @Contended Integer int_194 = new Integer(194);
+    @Contended Integer int_195 = new Integer(195);
+    @Contended Integer int_196 = new Integer(196);
+    @Contended Integer int_197 = new Integer(197);
+    @Contended Integer int_198 = new Integer(198);
+    @Contended Integer int_199 = new Integer(199);
+    @Contended Integer int_200 = new Integer(200);
+    @Contended Integer int_201 = new Integer(201);
+    @Contended Integer int_202 = new Integer(202);
+    @Contended Integer int_203 = new Integer(203);
+    @Contended Integer int_204 = new Integer(204);
+    @Contended Integer int_205 = new Integer(205);
+    @Contended Integer int_206 = new Integer(206);
+    @Contended Integer int_207 = new Integer(207);
+    @Contended Integer int_208 = new Integer(208);
+    @Contended Integer int_209 = new Integer(209);
+    @Contended Integer int_210 = new Integer(210);
+    @Contended Integer int_211 = new Integer(211);
+    @Contended Integer int_212 = new Integer(212);
+    @Contended Integer int_213 = new Integer(213);
+    @Contended Integer int_214 = new Integer(214);
+    @Contended Integer int_215 = new Integer(215);
+    @Contended Integer int_216 = new Integer(216);
+    @Contended Integer int_217 = new Integer(217);
+    @Contended Integer int_218 = new Integer(218);
+    @Contended Integer int_219 = new Integer(219);
+    @Contended Integer int_220 = new Integer(220);
+    @Contended Integer int_221 = new Integer(221);
+    @Contended Integer int_222 = new Integer(222);
+    @Contended Integer int_223 = new Integer(223);
+    @Contended Integer int_224 = new Integer(224);
+    @Contended Integer int_225 = new Integer(225);
+    @Contended Integer int_226 = new Integer(226);
+    @Contended Integer int_227 = new Integer(227);
+    @Contended Integer int_228 = new Integer(228);
+    @Contended Integer int_229 = new Integer(229);
+    @Contended Integer int_230 = new Integer(230);
+    @Contended Integer int_231 = new Integer(231);
+    @Contended Integer int_232 = new Integer(232);
+    @Contended Integer int_233 = new Integer(233);
+    @Contended Integer int_234 = new Integer(234);
+    @Contended Integer int_235 = new Integer(235);
+    @Contended Integer int_236 = new Integer(236);
+    @Contended Integer int_237 = new Integer(237);
+    @Contended Integer int_238 = new Integer(238);
+    @Contended Integer int_239 = new Integer(239);
+    @Contended Integer int_240 = new Integer(240);
+    @Contended Integer int_241 = new Integer(241);
+    @Contended Integer int_242 = new Integer(242);
+    @Contended Integer int_243 = new Integer(243);
+    @Contended Integer int_244 = new Integer(244);
+    @Contended Integer int_245 = new Integer(245);
+    @Contended Integer int_246 = new Integer(246);
+    @Contended Integer int_247 = new Integer(247);
+    @Contended Integer int_248 = new Integer(248);
+    @Contended Integer int_249 = new Integer(249);
+    @Contended Integer int_250 = new Integer(250);
+    @Contended Integer int_251 = new Integer(251);
+    @Contended Integer int_252 = new Integer(252);
+    @Contended Integer int_253 = new Integer(253);
+    @Contended Integer int_254 = new Integer(254);
+    @Contended Integer int_255 = new Integer(255);
+    @Contended Integer int_256 = new Integer(256);
+    @Contended Integer int_257 = new Integer(257);
+    @Contended Integer int_258 = new Integer(258);
+    @Contended Integer int_259 = new Integer(259);
+    @Contended Integer int_260 = new Integer(260);
+    @Contended Integer int_261 = new Integer(261);
+    @Contended Integer int_262 = new Integer(262);
+    @Contended Integer int_263 = new Integer(263);
+    @Contended Integer int_264 = new Integer(264);
+    @Contended Integer int_265 = new Integer(265);
+    @Contended Integer int_266 = new Integer(266);
+    @Contended Integer int_267 = new Integer(267);
+    @Contended Integer int_268 = new Integer(268);
+    @Contended Integer int_269 = new Integer(269);
+    @Contended Integer int_270 = new Integer(270);
+    @Contended Integer int_271 = new Integer(271);
+    @Contended Integer int_272 = new Integer(272);
+    @Contended Integer int_273 = new Integer(273);
+    @Contended Integer int_274 = new Integer(274);
+    @Contended Integer int_275 = new Integer(275);
+    @Contended Integer int_276 = new Integer(276);
+    @Contended Integer int_277 = new Integer(277);
+    @Contended Integer int_278 = new Integer(278);
+    @Contended Integer int_279 = new Integer(279);
+    @Contended Integer int_280 = new Integer(280);
+    @Contended Integer int_281 = new Integer(281);
+    @Contended Integer int_282 = new Integer(282);
+    @Contended Integer int_283 = new Integer(283);
+    @Contended Integer int_284 = new Integer(284);
+    @Contended Integer int_285 = new Integer(285);
+    @Contended Integer int_286 = new Integer(286);
+    @Contended Integer int_287 = new Integer(287);
+    @Contended Integer int_288 = new Integer(288);
+    @Contended Integer int_289 = new Integer(289);
+    @Contended Integer int_290 = new Integer(290);
+    @Contended Integer int_291 = new Integer(291);
+    @Contended Integer int_292 = new Integer(292);
+    @Contended Integer int_293 = new Integer(293);
+    @Contended Integer int_294 = new Integer(294);
+    @Contended Integer int_295 = new Integer(295);
+    @Contended Integer int_296 = new Integer(296);
+    @Contended Integer int_297 = new Integer(297);
+    @Contended Integer int_298 = new Integer(298);
+    @Contended Integer int_299 = new Integer(299);
+    @Contended Integer int_300 = new Integer(300);
+}