--- old/src/hotspot/os/linux/gc/z/zPhysicalMemoryBacking_linux.cpp	2020-02-19 09:04:35.041524037 +0100
+++ new/src/hotspot/os/linux/gc/z/zPhysicalMemoryBacking_linux.cpp	2020-02-19 09:04:34.708517305 +0100
@@ -137,16 +137,12 @@
   _block_size = buf.f_bsize;
   _available = buf.f_bavail * _block_size;
 
-  // Make sure we're on a supported filesystem
-  if (!is_tmpfs() && !is_hugetlbfs()) {
-    log_error(gc)("Backing file must be located on a %s or a %s filesystem",
-                  ZFILESYSTEM_TMPFS, ZFILESYSTEM_HUGETLBFS);
-    return;
-  }
+  log_info(gc, init)("Backing Filesystem: %s (0x" UINT64_FORMAT_X ")",
+                     is_tmpfs() ? ZFILESYSTEM_TMPFS : is_hugetlbfs() ? ZFILESYSTEM_HUGETLBFS : "other", _filesystem);
 
   // Make sure the filesystem type matches requested large page type
   if (ZLargePages::is_transparent() && !is_tmpfs()) {
-    log_error(gc)("-XX:+UseTransparentHugePages can only be enable when using a %s filesystem",
+    log_error(gc)("-XX:+UseTransparentHugePages can only be enabled when using a %s filesystem",
                   ZFILESYSTEM_TMPFS);
     return;
   }
@@ -169,10 +165,22 @@
     return;
   }
 
-  const size_t expected_block_size = is_tmpfs() ? os::vm_page_size() : os::large_page_size();
-  if (expected_block_size != _block_size) {
+  if (ZLargePages::is_explicit() && os::large_page_size() != ZGranuleSize) {
+    log_error(gc)("Incompatible large page size configured " SIZE_FORMAT " (expected " SIZE_FORMAT ")",
+                  os::large_page_size(), ZGranuleSize);
+    return;
+  }
+
+  // Make sure the filesystem block size is compatible
+  if (ZGranuleSize % _block_size != 0) {
+    log_error(gc)("Filesystem backing the heap has incompatible block size (" SIZE_FORMAT ")",
+                  _block_size);
+    return;
+  }
+
+  if (is_hugetlbfs() && _block_size != ZGranuleSize) {
     log_error(gc)("%s filesystem has unexpected block size " SIZE_FORMAT " (expected " SIZE_FORMAT ")",
-                  is_tmpfs() ? ZFILESYSTEM_TMPFS : ZFILESYSTEM_HUGETLBFS, _block_size, expected_block_size);
+                  ZFILESYSTEM_HUGETLBFS, _block_size, ZGranuleSize);
     return;
   }
 
@@ -195,7 +203,7 @@
     return -1;
   }
 
-  log_info(gc, init)("Heap backed by file: /memfd:%s", filename);
+  log_info(gc, init)("Backing File: /memfd:%s", filename);
 
   return fd;
 }
@@ -231,7 +239,7 @@
       return -1;
     }
 
-    log_info(gc, init)("Heap backed by file: %s/#" UINT64_FORMAT, mountpoint.get(), (uint64_t)stat_buf.st_ino);
+    log_info(gc, init)("Backing File: %s/#" UINT64_FORMAT, mountpoint.get(), (uint64_t)stat_buf.st_ino);
 
     return fd_anon;
   }
@@ -257,7 +265,7 @@
     return -1;
   }
 
-  log_info(gc, init)("Heap backed by file: %s", filename);
+  log_info(gc, init)("Backing File: %s", filename);
 
   return fd;
 }
--- /dev/null	2020-01-07 09:26:22.747784373 +0100
+++ new/test/hotspot/jtreg/gc/z/TestAllocateHeapAt.java	2020-02-19 09:04:35.160526442 +0100
@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2020, 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 Public 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 Public 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 Public 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.
+ */
+
+package gc.z;
+
+/*
+ * @test TestAllocateHeapAt
+ * @requires vm.gc.Z & os.family == "linux" & !vm.graal.enabled
+ * @summary Test ZGC with -XX:AllocateHeapAt
+ * @library /test/lib
+ * @run main/othervm gc.z.TestAllocateHeapAt . true
+ * @run main/othervm gc.z.TestAllocateHeapAt non-existing-directory false
+ */
+
+import jdk.test.lib.process.ProcessTools;
+
+public class TestAllocateHeapAt {
+    public static void main(String[] args) throws Exception {
+        final String directory = args[0];
+        final boolean exists = Boolean.parseBoolean(args[1]);
+        final String backingFile = "Backing File: " + directory;
+        final String failedToCreateFile = "Failed to create file " + directory;
+
+        ProcessTools.executeProcess(ProcessTools.createJavaProcessBuilder(new String[] {
+                "-XX:+UnlockExperimentalVMOptions",
+                "-XX:+UseZGC",
+                "-Xlog:gc*",
+                "-Xms32M",
+                "-Xmx32M",
+                "-XX:AllocateHeapAt=" + directory,
+                "-version" }))
+            .shouldContain(exists ? backingFile : failedToCreateFile)
+            .shouldNotContain(exists ? failedToCreateFile : backingFile)
+            .shouldHaveExitValue(exists ? 0 : 1);
+    }
+}