--- /dev/null	2018-04-03 12:55:20.301839954 +0200
+++ new/src/hotspot/os_cpu/linux_x86/gc/z/zPhysicalMemoryBacking_linux_x86.cpp	2018-06-01 22:30:13.736720932 +0200
@@ -0,0 +1,238 @@
+/*
+ * Copyright (c) 2015, 2018, 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.
+ */
+
+#include "precompiled.hpp"
+#include "gc/z/zAddress.inline.hpp"
+#include "gc/z/zBackingFile_linux_x86.hpp"
+#include "gc/z/zErrno.hpp"
+#include "gc/z/zFlags.hpp"
+#include "gc/z/zLargePages.inline.hpp"
+#include "gc/z/zMemory.hpp"
+#include "gc/z/zNUMA.hpp"
+#include "gc/z/zPhysicalMemory.inline.hpp"
+#include "gc/z/zPhysicalMemoryBacking_linux_x86.hpp"
+#include "logging/log.hpp"
+#include "runtime/os.hpp"
+#include "utilities/align.hpp"
+#include "utilities/debug.hpp"
+
+#include <stdio.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+
+// Support for building on older Linux systems
+#ifndef MADV_HUGEPAGE
+#define MADV_HUGEPAGE                        14
+#endif
+
+// Proc file entry for max map mount
+#define ZFILENAME_PROC_MAX_MAP_COUNT         "/proc/sys/vm/max_map_count"
+
+ZPhysicalMemoryBacking::ZPhysicalMemoryBacking(size_t max_capacity, size_t granule_size) :
+    _manager(),
+    _file(),
+    _granule_size(granule_size) {
+
+  // Check and warn if max map count seems too low
+  check_max_map_count(max_capacity, granule_size);
+}
+
+void ZPhysicalMemoryBacking::check_max_map_count(size_t max_capacity, size_t granule_size) const {
+  const char* const filename = ZFILENAME_PROC_MAX_MAP_COUNT;
+  FILE* const file = fopen(filename, "r");
+  if (file == NULL) {
+    // Failed to open file, skip check
+    log_debug(gc)("Failed to open %s", filename);
+    return;
+  }
+
+  size_t actual_max_map_count = 0;
+  const int result = fscanf(file, SIZE_FORMAT, &actual_max_map_count);
+  fclose(file);
+  if (result != 1) {
+    // Failed to read file, skip check
+    log_debug(gc)("Failed to read %s", filename);
+    return;
+  }
+
+  // The required max map count is impossible to calculate exactly since subsystems
+  // other than ZGC are also creating memory mappings, and we have no control over that.
+  // However, ZGC tends to create the most mappings and dominate the total count.
+  // In the worst cases, ZGC will map each granule three times, i.e. once per heap view.
+  // We speculate that we need another 20% to allow for non-ZGC subsystems to map memory.
+  const size_t required_max_map_count = (max_capacity / granule_size) * 3 * 1.2;
+  if (actual_max_map_count < required_max_map_count) {
+    log_warning(gc)("The system limit on number of memory mappings "
+                    "per process might be too low for the given");
+    log_warning(gc)("Java heap size (" SIZE_FORMAT "M). Please "
+                    "adjust %s to allow for at least", max_capacity / M, filename);
+    log_warning(gc)(SIZE_FORMAT " mappings (current limit is " SIZE_FORMAT "). "
+                    "Continuing execution with the current limit could",
+                    required_max_map_count, actual_max_map_count);
+    log_warning(gc)("lead to a fatal error down the line, due to failed "
+                    "attempts to map memory.");
+  }
+}
+
+bool ZPhysicalMemoryBacking::is_initialized() const {
+  return _file.is_initialized();
+}
+
+bool ZPhysicalMemoryBacking::expand(size_t from, size_t to) {
+  const size_t size = to - from;
+
+  // Expand
+  if (!_file.expand(from, size)) {
+    return false;
+  }
+
+  // Add expanded space to free list
+  _manager.free(from, size);
+
+  return true;
+}
+
+ZPhysicalMemory ZPhysicalMemoryBacking::alloc(size_t size) {
+  assert(is_aligned(size, _granule_size), "Invalid size");
+
+  ZPhysicalMemory pmem;
+
+  // Allocate segments
+  for (size_t allocated = 0; allocated < size; allocated += _granule_size) {
+    const uintptr_t start = _manager.alloc_from_front(_granule_size);
+    assert(start != UINTPTR_MAX, "Allocation should never fail");
+    pmem.add_segment(ZPhysicalMemorySegment(start, _granule_size));
+  }
+
+  return pmem;
+}
+
+void ZPhysicalMemoryBacking::free(ZPhysicalMemory pmem) {
+  const size_t nsegments = pmem.nsegments();
+
+  // Free segments
+  for (size_t i = 0; i < nsegments; i++) {
+    const ZPhysicalMemorySegment segment = pmem.segment(i);
+    _manager.free(segment.start(), segment.size());
+  }
+}
+
+void ZPhysicalMemoryBacking::map_failed(ZErrno err) const {
+  if (err == ENOMEM) {
+    fatal("Failed to map memory. Please check the system limit on number of "
+          "memory mappings allowed per process (see %s)", ZFILENAME_PROC_MAX_MAP_COUNT);
+  } else {
+    fatal("Failed to map memory (%s)", err.to_string());
+  }
+}
+
+void ZPhysicalMemoryBacking::advise_view(uintptr_t addr, size_t size) const {
+  if (madvise((void*)addr, size, MADV_HUGEPAGE) == -1) {
+    ZErrno err;
+    log_error(gc)("Failed to advise use of transparent huge pages (%s)", err.to_string());
+  }
+}
+
+void ZPhysicalMemoryBacking::pretouch_view(uintptr_t addr, size_t size) const {
+  const size_t page_size = ZLargePages::is_explicit() ? os::large_page_size() : os::vm_page_size();
+  os::pretouch_memory((void*)addr, (void*)(addr + size), page_size);
+}
+
+void ZPhysicalMemoryBacking::map_view(ZPhysicalMemory pmem, uintptr_t addr, bool pretouch) const {
+  const size_t nsegments = pmem.nsegments();
+
+  // Map segments
+  for (size_t i = 0; i < nsegments; i++) {
+    const ZPhysicalMemorySegment segment = pmem.segment(i);
+    const size_t size = segment.size();
+    const void* const res = mmap((void*)addr, size, PROT_READ|PROT_WRITE, MAP_FIXED|MAP_SHARED, _file.fd(), segment.start());
+    if (res == MAP_FAILED) {
+      ZErrno err;
+      map_failed(err);
+    }
+
+    // Advise on use of transparent huge pages before touching it
+    if (ZLargePages::is_transparent()) {
+      advise_view(addr, size);
+    }
+
+    // NUMA interleave memory before touching it
+    ZNUMA::memory_interleave(addr, size);
+
+    if (pretouch) {
+      pretouch_view(addr, size);
+    }
+
+    addr += size;
+  }
+}
+
+void ZPhysicalMemoryBacking::unmap_view(ZPhysicalMemory pmem, uintptr_t addr) const {
+  // Note that we must keep the address space reservation intact and just detach
+  // the backing memory. For this reason we map a new anonymous, non-accessible
+  // and non-reserved page over the mapping instead of actually unmapping.
+  const size_t size = pmem.size();
+  const void* const res = mmap((void*)addr, size, PROT_NONE, MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE|MAP_NORESERVE, -1, 0);
+  if (res == MAP_FAILED) {
+    ZErrno err;
+    map_failed(err);
+  }
+}
+
+uintptr_t ZPhysicalMemoryBacking::nmt_address(uintptr_t offset) const {
+  // From an NMT point of view we treat the first heap mapping (marked0) as committed
+  return ZAddress::marked0(offset);
+}
+
+void ZPhysicalMemoryBacking::map(ZPhysicalMemory pmem, uintptr_t offset) const {
+  if (ZUnmapBadViews) {
+    // Only map the good view, for debugging only
+    map_view(pmem, ZAddress::good(offset), AlwaysPreTouch);
+  } else {
+    // Map all views
+    map_view(pmem, ZAddress::marked0(offset), AlwaysPreTouch);
+    map_view(pmem, ZAddress::marked1(offset), AlwaysPreTouch);
+    map_view(pmem, ZAddress::remapped(offset), AlwaysPreTouch);
+  }
+}
+
+void ZPhysicalMemoryBacking::unmap(ZPhysicalMemory pmem, uintptr_t offset) const {
+  if (ZUnmapBadViews) {
+    // Only map the good view, for debugging only
+    unmap_view(pmem, ZAddress::good(offset));
+  } else {
+    // Unmap all views
+    unmap_view(pmem, ZAddress::marked0(offset));
+    unmap_view(pmem, ZAddress::marked1(offset));
+    unmap_view(pmem, ZAddress::remapped(offset));
+  }
+}
+
+void ZPhysicalMemoryBacking::flip(ZPhysicalMemory pmem, uintptr_t offset) const {
+  assert(ZUnmapBadViews, "Should be enabled");
+  const uintptr_t addr_good = ZAddress::good(offset);
+  const uintptr_t addr_bad = ZAddress::is_marked(ZAddressGoodMask) ? ZAddress::remapped(offset) : ZAddress::marked(offset);
+  // Map/Unmap views
+  map_view(pmem, addr_good, false /* pretouch */);
+  unmap_view(pmem, addr_bad);
+}