8224817: Implementation of JEP 364: ZGC on macOS

Reviewed-by: pliden, stefank

make/autoconf/hotspot.m4

@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2011, 2018, Oracle and/or its affiliates. All rights reserved.
+# Copyright (c) 2011, 2019, 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
@@ -351,7 +351,8 @@ AC_DEFUN_ONCE([HOTSPOT_SETUP_JVM_FEATURES],
   # Only enable ZGC on supported platforms
   AC_MSG_CHECKING([if zgc can be built])
   if (test "x$OPENJDK_TARGET_OS" = "xlinux" && test "x$OPENJDK_TARGET_CPU" = "xx86_64") || \
-     (test "x$OPENJDK_TARGET_OS" = "xlinux" && test "x$OPENJDK_TARGET_CPU" = "xaarch64"); then
+     (test "x$OPENJDK_TARGET_OS" = "xlinux" && test "x$OPENJDK_TARGET_CPU" = "xaarch64") ||
+     (test "x$OPENJDK_TARGET_OS" = "xmacosx" && test "x$OPENJDK_TARGET_CPU" = "xx86_64"); then
     AC_MSG_RESULT([yes])
   else
     DISABLED_JVM_FEATURES="$DISABLED_JVM_FEATURES zgc"

src/hotspot/os/bsd/gc/z/zBackingFile_bsd.cpp

@@ -0,0 +1,183 @@
+/*
+ * Copyright (c) 2019, 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/zBackingFile_bsd.hpp"
+#include "gc/z/zErrno.hpp"
+#include "gc/z/zGlobals.hpp"
+#include "gc/z/zLargePages.inline.hpp"
+#include "gc/z/zPhysicalMemory.inline.hpp"
+#include "logging/log.hpp"
+#include "runtime/globals.hpp"
+#include "runtime/os.hpp"
+#include "utilities/align.hpp"
+#include "utilities/debug.hpp"
+
+#include <mach/mach.h>
+#include <mach/mach_vm.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+
+static int vm_flags_superpage() {
+  if (!ZLargePages::is_explicit()) {
+    return 0;
+  }
+
+  const int page_size_in_megabytes = ZGranuleSize >> 20;
+  return page_size_in_megabytes << VM_FLAGS_SUPERPAGE_SHIFT;
+}
+
+static ZErrno mremap(uintptr_t from_addr, uintptr_t to_addr, size_t size) {
+  mach_vm_address_t remap_addr = to_addr;
+  vm_prot_t remap_cur_prot;
+  vm_prot_t remap_max_prot;
+
+  // Remap memory to an additional location
+  const kern_return_t res = mach_vm_remap(mach_task_self(),
+                                          &remap_addr,
+                                          size,
+                                          0 /* mask */,
+                                          VM_FLAGS_FIXED | VM_FLAGS_OVERWRITE | vm_flags_superpage(),
+                                          mach_task_self(),
+                                          from_addr,
+                                          FALSE /* copy */,
+                                          &remap_cur_prot,
+                                          &remap_max_prot,
+                                          VM_INHERIT_COPY);
+
+  return (res == KERN_SUCCESS) ? ZErrno(0) : ZErrno(EINVAL);
+}
+
+ZBackingFile::ZBackingFile() :
+    _base(0),
+    _size(0),
+    _initialized(false) {
+
+  // Reserve address space for virtual backing file
+  _base = (uintptr_t)os::reserve_memory(MaxHeapSize);
+  if (_base == 0) {
+    // Failed
+    log_error(gc)("Failed to reserve address space for virtual backing file");
+    return;
+  }
+
+  // Successfully initialized
+  _initialized = true;
+}
+
+bool ZBackingFile::is_initialized() const {
+  return _initialized;
+}
+
+size_t ZBackingFile::size() const {
+  return _size;
+}
+
+bool ZBackingFile::commit_inner(size_t offset, size_t length) {
+  assert(is_aligned(offset, os::vm_page_size()), "Invalid offset");
+  assert(is_aligned(length, os::vm_page_size()), "Invalid length");
+
+  log_trace(gc, heap)("Committing memory: " SIZE_FORMAT "M-" SIZE_FORMAT "M (" SIZE_FORMAT "M)",
+                      offset / M, (offset + length) / M, length / M);
+
+  const uintptr_t addr = _base + offset;
+  const void* const res = mmap((void*)addr, length, PROT_READ | PROT_WRITE, MAP_FIXED | MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+  if (res == MAP_FAILED) {
+    ZErrno err;
+    log_error(gc)("Failed to commit memory (%s)", err.to_string());
+    return false;
+  }
+
+  const size_t end = offset + length;
+  if (end > _size) {
+    // Record new virtual file size
+    _size = end;
+  }
+
+  // Success
+  return true;
+}
+
+size_t ZBackingFile::commit(size_t offset, size_t length) {
+  // Try to commit the whole region
+  if (commit_inner(offset, length)) {
+    // Success
+    return length;
+  }
+
+  // Failed, try to commit as much as possible
+  size_t start = offset;
+  size_t end = offset + length;
+
+  for (;;) {
+    length = align_down((end - start) / 2, ZGranuleSize);
+    if (length == 0) {
+      // Done, don't commit more
+      return start - offset;
+    }
+
+    if (commit_inner(start, length)) {
+      // Success, try commit more
+      start += length;
+    } else {
+      // Failed, try commit less
+      end -= length;
+    }
+  }
+}
+
+size_t ZBackingFile::uncommit(size_t offset, size_t length) {
+  assert(is_aligned(offset, os::vm_page_size()), "Invalid offset");
+  assert(is_aligned(length, os::vm_page_size()), "Invalid length");
+
+  log_trace(gc, heap)("Uncommitting memory: " SIZE_FORMAT "M-" SIZE_FORMAT "M (" SIZE_FORMAT "M)",
+                      offset / M, (offset + length) / M, length / M);
+
+  const uintptr_t start = _base + offset;
+  const void* const res = mmap((void*)start, length, PROT_NONE, MAP_FIXED | MAP_ANONYMOUS | MAP_PRIVATE | MAP_NORESERVE, -1, 0);
+  if (res == MAP_FAILED) {
+    ZErrno err;
+    log_error(gc)("Failed to uncommit memory (%s)", err.to_string());
+    return 0;
+  }
+
+  return length;
+}
+
+void ZBackingFile::map(uintptr_t addr, size_t size, uintptr_t offset) const {
+  const ZErrno err = mremap(_base + offset, addr, size);
+  if (err) {
+    fatal("Failed to remap memory (%s)", err.to_string());
+  }
+}
+
+void ZBackingFile::unmap(uintptr_t addr, size_t size) 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 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;
+    fatal("Failed to map memory (%s)", err.to_string());
+  }
+}

src/hotspot/os/bsd/gc/z/zBackingFile_bsd.hpp

@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 2019, 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.
+ */
+
+#ifndef OS_BSD_GC_Z_ZBACKINGFILE_BSD_HPP
+#define OS_BSD_GC_Z_ZBACKINGFILE_BSD_HPP
+
+#include "memory/allocation.hpp"
+
+class ZPhysicalMemory;
+
+// On macOS, we use a virtual backing file. It is represented by a reserved virtual
+// address space, in which we commit physical memory using the mach_vm_map() API.
+// The multi-mapping API simply remaps these addresses using mach_vm_remap() into
+// the different heap views. This works as-if there was a backing file, it's just
+// that the file is represented with memory mappings instead.
+
+class ZBackingFile {
+private:
+  uintptr_t _base;
+  size_t    _size;
+  bool      _initialized;
+
+  bool commit_inner(size_t offset, size_t length);
+
+public:
+  ZBackingFile();
+
+  bool is_initialized() const;
+
+  size_t size() const;
+
+  size_t commit(size_t offset, size_t length);
+  size_t uncommit(size_t offset, size_t length);
+
+  void map(uintptr_t addr, size_t size, uintptr_t offset) const;
+  void unmap(uintptr_t addr, size_t size) const;
+};
+
+#endif // OS_BSD_GC_Z_ZBACKINGFILE_BSD_HPP

src/hotspot/os/bsd/gc/z/zLargePages_bsd.cpp

@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2019, 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/zLargePages.hpp"
+#include "runtime/globals.hpp"
+
+void ZLargePages::initialize_platform() {
+  if (UseLargePages) {
+    _state = Explicit;
+  } else {
+    _state = Disabled;
+  }
+}

src/hotspot/os/bsd/gc/z/zNUMA_bsd.cpp

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2019, 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/zNUMA.hpp"
+
+void ZNUMA::initialize_platform() {
+  _enabled = false;
+}
+
+uint32_t ZNUMA::count() {
+  return 1;
+}
+
+uint32_t ZNUMA::id() {
+  return 0;
+}
+
+uint32_t ZNUMA::memory_id(uintptr_t addr) {
+  // NUMA support not enabled, assume everything belongs to node zero
+  return 0;
+}

src/hotspot/os/bsd/gc/z/zPhysicalMemoryBacking_bsd.cpp

@@ -0,0 +1,212 @@
+/*
+ * Copyright (c) 2019, 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/zGlobals.hpp"
+#include "gc/z/zLargePages.inline.hpp"
+#include "gc/z/zPhysicalMemory.inline.hpp"
+#include "gc/z/zPhysicalMemoryBacking_bsd.hpp"
+#include "runtime/globals.hpp"
+#include "runtime/init.hpp"
+#include "runtime/os.hpp"
+#include "utilities/align.hpp"
+#include "utilities/debug.hpp"
+
+bool ZPhysicalMemoryBacking::is_initialized() const {
+  return _file.is_initialized();
+}
+
+void ZPhysicalMemoryBacking::warn_commit_limits(size_t max) const {
+  // Does nothing
+}
+
+bool ZPhysicalMemoryBacking::supports_uncommit() {
+  assert(!is_init_completed(), "Invalid state");
+  assert(_file.size() >= ZGranuleSize, "Invalid size");
+
+  // Test if uncommit is supported by uncommitting and then re-committing a granule
+  return commit(uncommit(ZGranuleSize)) == ZGranuleSize;
+}
+
+size_t ZPhysicalMemoryBacking::commit(size_t size) {
+  size_t committed = 0;
+
+  // Fill holes in the backing file
+  while (committed < size) {
+    size_t allocated = 0;
+    const size_t remaining = size - committed;
+    const uintptr_t start = _uncommitted.alloc_from_front_at_most(remaining, &allocated);
+    if (start == UINTPTR_MAX) {
+      // No holes to commit
+      break;
+    }
+
+    // Try commit hole
+    const size_t filled = _file.commit(start, allocated);
+    if (filled > 0) {
+      // Successful or partialy successful
+      _committed.free(start, filled);
+      committed += filled;
+    }
+    if (filled < allocated) {
+      // Failed or partialy failed
+      _uncommitted.free(start + filled, allocated - filled);
+      return committed;
+    }
+  }
+
+  // Expand backing file
+  if (committed < size) {
+    const size_t remaining = size - committed;
+    const uintptr_t start = _file.size();
+    const size_t expanded = _file.commit(start, remaining);
+    if (expanded > 0) {
+      // Successful or partialy successful
+      _committed.free(start, expanded);
+      committed += expanded;
+    }
+  }
+
+  return committed;
+}
+
+size_t ZPhysicalMemoryBacking::uncommit(size_t size) {
+  size_t uncommitted = 0;
+
+  // Punch holes in backing file
+  while (uncommitted < size) {
+    size_t allocated = 0;
+    const size_t remaining = size - uncommitted;
+    const uintptr_t start = _committed.alloc_from_back_at_most(remaining, &allocated);
+    assert(start != UINTPTR_MAX, "Allocation should never fail");
+
+    // Try punch hole
+    const size_t punched = _file.uncommit(start, allocated);
+    if (punched > 0) {
+      // Successful or partialy successful
+      _uncommitted.free(start, punched);
+      uncommitted += punched;
+    }
+    if (punched < allocated) {
+      // Failed or partialy failed
+      _committed.free(start + punched, allocated - punched);
+      return uncommitted;
+    }
+  }
+
+  return uncommitted;
+}
+
+ZPhysicalMemory ZPhysicalMemoryBacking::alloc(size_t size) {
+  assert(is_aligned(size, ZGranuleSize), "Invalid size");
+
+  ZPhysicalMemory pmem;
+
+  // Allocate segments
+  for (size_t allocated = 0; allocated < size; allocated += ZGranuleSize) {
+    const uintptr_t start = _committed.alloc_from_front(ZGranuleSize);
+    assert(start != UINTPTR_MAX, "Allocation should never fail");
+    pmem.add_segment(ZPhysicalMemorySegment(start, ZGranuleSize));
+  }
+
+  return pmem;
+}
+
+void ZPhysicalMemoryBacking::free(const ZPhysicalMemory& pmem) {
+  const size_t nsegments = pmem.nsegments();
+
+  // Free segments
+  for (size_t i = 0; i < nsegments; i++) {
+    const ZPhysicalMemorySegment& segment = pmem.segment(i);
+    _committed.free(segment.start(), segment.size());
+  }
+}
+
+void ZPhysicalMemoryBacking::pretouch_view(uintptr_t addr, size_t size) const {
+  const size_t page_size = ZLargePages::is_explicit() ? ZGranuleSize : os::vm_page_size();
+  os::pretouch_memory((void*)addr, (void*)(addr + size), page_size);
+}
+
+void ZPhysicalMemoryBacking::map_view(const ZPhysicalMemory& pmem, uintptr_t addr, bool pretouch) const {
+  const size_t nsegments = pmem.nsegments();
+  size_t size = 0;
+
+  // Map segments
+  for (size_t i = 0; i < nsegments; i++) {
+    const ZPhysicalMemorySegment& segment = pmem.segment(i);
+    const uintptr_t segment_addr = addr + size;
+    _file.map(segment_addr, segment.size(), segment.start());
+    size += segment.size();
+  }
+
+  // Pre-touch memory
+  if (pretouch) {
+    pretouch_view(addr, size);
+  }
+}
+
+void ZPhysicalMemoryBacking::unmap_view(const ZPhysicalMemory& pmem, uintptr_t addr) const {
+  _file.unmap(addr, pmem.size());
+}
+
+uintptr_t ZPhysicalMemoryBacking::nmt_address(uintptr_t offset) const {
+  // From an NMT point of view we treat the first heap view (marked0) as committed
+  return ZAddress::marked0(offset);
+}
+
+void ZPhysicalMemoryBacking::map(const ZPhysicalMemory& pmem, uintptr_t offset) const {
+  if (ZVerifyViews) {
+    // Map good view
+    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(const ZPhysicalMemory& pmem, uintptr_t offset) const {
+  if (ZVerifyViews) {
+    // Unmap good view
+    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::debug_map(const ZPhysicalMemory& pmem, uintptr_t offset) const {
+  // Map good view
+  assert(ZVerifyViews, "Should be enabled");
+  map_view(pmem, ZAddress::good(offset), false /* pretouch */);
+}
+
+void ZPhysicalMemoryBacking::debug_unmap(const ZPhysicalMemory& pmem, uintptr_t offset) const {
+  // Unmap good view
+  assert(ZVerifyViews, "Should be enabled");
+  unmap_view(pmem, ZAddress::good(offset));
+}

src/hotspot/os/bsd/gc/z/zPhysicalMemoryBacking_bsd.hpp

@@ -0,0 +1,63 @@
+/*
+ * Copyright (c) 2019, 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.
+ */
+
+#ifndef OS_BSD_GC_Z_ZPHYSICALMEMORYBACKING_BSD_HPP
+#define OS_BSD_GC_Z_ZPHYSICALMEMORYBACKING_BSD_HPP
+
+#include "gc/z/zBackingFile_bsd.hpp"
+#include "gc/z/zMemory.hpp"
+
+class ZPhysicalMemory;
+
+class ZPhysicalMemoryBacking {
+private:
+  ZBackingFile   _file;
+  ZMemoryManager _committed;
+  ZMemoryManager _uncommitted;
+
+  void pretouch_view(uintptr_t addr, size_t size) const;
+  void map_view(const ZPhysicalMemory& pmem, uintptr_t addr, bool pretouch) const;
+  void unmap_view(const ZPhysicalMemory& pmem, uintptr_t addr) const;
+
+public:
+  bool is_initialized() const;
+
+  void warn_commit_limits(size_t max) const;
+  bool supports_uncommit();
+
+  size_t commit(size_t size);
+  size_t uncommit(size_t size);
+
+  ZPhysicalMemory alloc(size_t size);
+  void free(const ZPhysicalMemory& pmem);
+
+  uintptr_t nmt_address(uintptr_t offset) const;
+
+  void map(const ZPhysicalMemory& pmem, uintptr_t offset) const;
+  void unmap(const ZPhysicalMemory& pmem, uintptr_t offset) const;
+
+  void debug_map(const ZPhysicalMemory& pmem, uintptr_t offset) const;
+  void debug_unmap(const ZPhysicalMemory& pmem, uintptr_t offset) const;
+};
+
+#endif // OS_BSD_GC_Z_ZPHYSICALMEMORYBACKING_BSD_HPP