src/hotspot/share/gc/z/zMarkStackAllocator.cpp

/*
 * Copyright (c) 2016, 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
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 */

#include "precompiled.hpp"
#include "gc/z/zLock.inline.hpp"
#include "gc/z/zMarkStack.inline.hpp"
#include "gc/z/zMarkStackAllocator.hpp"
#include "logging/log.hpp"
#include "runtime/atomic.hpp"
#include "runtime/os.hpp"
#include "utilities/debug.hpp"

uintptr_t ZMarkStackSpaceStart;

ZMarkStackSpace::ZMarkStackSpace() :
    _expand_lock(),
    _start(0),
    _top(0),
    _end(0) {
  assert(ZMarkStackSpaceLimit >= ZMarkStackSpaceExpandSize, "ZMarkStackSpaceLimit too small");

  // Reserve address space
  const size_t size = ZMarkStackSpaceLimit;
  const size_t alignment = (size_t)os::vm_allocation_granularity();
  const uintptr_t addr = (uintptr_t)os::reserve_memory(size, NULL, alignment, mtGC);
  if (addr == 0) {
    log_error(gc, marking)("Failed to reserve address space for mark stacks");
    return;
  }

  // Successfully initialized
  _start = _top = _end = addr;

  // Register mark stack space start
  ZMarkStackSpaceStart = _start;
}

bool ZMarkStackSpace::is_initialized() const {
  return _start != 0;
}

uintptr_t ZMarkStackSpace::alloc_space(size_t size) {
  uintptr_t top = Atomic::load(&_top);

  for (;;) {
    const uintptr_t end = Atomic::load(&_end);
    const uintptr_t new_top = top + size;
    if (new_top > end) {
      // Not enough space left
      return 0;
    }

    const uintptr_t prev_top = Atomic::cmpxchg(new_top, &_top, top);
    if (prev_top == top) {
      // Success
      return top;
    }

    // Retry
    top = prev_top;
  }
}

uintptr_t ZMarkStackSpace::expand_and_alloc_space(size_t size) {
  ZLocker<ZLock> locker(&_expand_lock);

  // Retry allocation before expanding
  uintptr_t addr = alloc_space(size);
  if (addr != 0) {
    return addr;
  }

  // Check expansion limit
  const size_t expand_size = ZMarkStackSpaceExpandSize;
  const size_t old_size = _end - _start;
  const size_t new_size = old_size + expand_size;
  if (new_size > ZMarkStackSpaceLimit) {
    // Expansion limit reached. This is a fatal error since we
    // currently can't recover from running out of mark stack space.
    fatal("Mark stack space exhausted. Use -XX:ZMarkStackSpaceLimit=<size> to increase the "
          "maximum number of bytes allocated for mark stacks. Current limit is " SIZE_FORMAT "M.",
          ZMarkStackSpaceLimit / M);
  }

  log_debug(gc, marking)("Expanding mark stack space: " SIZE_FORMAT "M->" SIZE_FORMAT "M",
                         old_size / M, new_size / M);

  // Expand
  os::commit_memory_or_exit((char*)_end, expand_size, false /* executable */, "Mark stack space");

  // Increment top before end to make sure another
  // thread can't steal out newly expanded space.
  addr = Atomic::add(size, &_top) - size;
  Atomic::add(expand_size, &_end);

  return addr;
}

uintptr_t ZMarkStackSpace::alloc(size_t size) {
  const uintptr_t addr = alloc_space(size);
  if (addr != 0) {
    return addr;
  }

  return expand_and_alloc_space(size);
}

ZMarkStackAllocator::ZMarkStackAllocator() :
    _freelist(),
    _space() {
  guarantee(sizeof(ZMarkStack) == ZMarkStackSize, "Size mismatch");
  guarantee(sizeof(ZMarkStackMagazine) <= ZMarkStackSize, "Size mismatch");

  // Prime free list to avoid an immediate space
  // expansion when marking starts.
  if (_space.is_initialized()) {
    prime_freelist();
  }
}

bool ZMarkStackAllocator::is_initialized() const {
  return _space.is_initialized();
}

void ZMarkStackAllocator::prime_freelist() {
  for (size_t size = 0; size < ZMarkStackSpaceExpandSize; size += ZMarkStackMagazineSize) {
    const uintptr_t addr = _space.alloc(ZMarkStackMagazineSize);
    ZMarkStackMagazine* const magazine = create_magazine_from_space(addr, ZMarkStackMagazineSize);
    free_magazine(magazine);
  }
}

ZMarkStackMagazine* ZMarkStackAllocator::create_magazine_from_space(uintptr_t addr, size_t size) {
  assert(is_aligned(size, ZMarkStackSize), "Invalid size");

  // Use first stack as magazine
  ZMarkStackMagazine* const magazine = new ((void*)addr) ZMarkStackMagazine();
  for (size_t i = ZMarkStackSize; i < size; i += ZMarkStackSize) {
    ZMarkStack* const stack = new ((void*)(addr + i)) ZMarkStack();
    const bool success = magazine->push(stack);
    assert(success, "Magazine should never get full");
  }

  return magazine;
}

ZMarkStackMagazine* ZMarkStackAllocator::alloc_magazine() {
  // Try allocating from the free list first
  ZMarkStackMagazine* const magazine = _freelist.pop_atomic();
  if (magazine != NULL) {
    return magazine;
  }

  // Allocate new magazine
  const uintptr_t addr = _space.alloc(ZMarkStackMagazineSize);
  if (addr == 0) {
    return NULL;
  }

  return create_magazine_from_space(addr, ZMarkStackMagazineSize);
}

void ZMarkStackAllocator::free_magazine(ZMarkStackMagazine* magazine) {
  _freelist.push_atomic(magazine);
}