src/hotspot/share/gc/z/zMarkStack.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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

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

#include <sys/mman.h>
#include <sys/types.h>

ZMarkStackSpace::ZMarkStackSpace() :
    _expand_lock(),
    _top(0),
    _end(0) {
  assert(ZMarkStacksMax >= ZMarkStackSpaceExpandSize, "ZMarkStacksMax too small");
  assert(ZMarkStacksMax <= ZMarkStackSpaceSize, "ZMarkStacksMax too large");

  // Reserve address space
  const void* res = mmap((void*)ZMarkStackSpaceStart, ZMarkStackSpaceSize,
                         PROT_NONE, MAP_ANONYMOUS|MAP_PRIVATE|MAP_NORESERVE, -1, 0);
  if (res != (void*)ZMarkStackSpaceStart) {
    log_error(gc, marking)("Failed to reserve address space for marking stacks");
    return;
  }

  // Successfully initialized
  _top = _end = ZMarkStackSpaceStart;
}

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

bool ZMarkStackSpace::expand() {
  const size_t max = ZMarkStackSpaceStart + ZMarkStacksMax;
  if (_end + ZMarkStackSpaceExpandSize > max) {
    // Expansion limit reached
    return false;
  }

  void* const res = mmap((void*)_end, ZMarkStackSpaceExpandSize,
                         PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE|MAP_FIXED, -1, 0);
  if (res == MAP_FAILED) {
    ZErrno err;
    log_error(gc, marking)("Failed to map memory for marking stacks (%s)", err.to_string());
    return false;
  }

  return true;
}

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

  for (;;) {
    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 locker(&_expand_lock);

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

  // Expand stack space
  if (!expand()) {
    // We currently can't handle the situation where we
    // are running out of mark stack space.
    fatal("Mark stack overflow (allocated " SIZE_FORMAT "M, size " SIZE_FORMAT "M, max " SIZE_FORMAT "M),"
          " use -XX:ZMarkStacksMax=? to increase this limit",
          (_end - ZMarkStackSpaceStart) / M, size / M, ZMarkStacksMax / M);
    return 0;
  }

  log_debug(gc, marking)("Expanding mark stack space: " SIZE_FORMAT "M->" SIZE_FORMAT "M",
                         (_end - ZMarkStackSpaceStart) / M,
                         (_end - ZMarkStackSpaceStart + ZMarkStackSpaceExpandSize) / M);

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

  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);
}

ZMarkStripe::ZMarkStripe() :
    _published(),
    _overflowed() {}

ZMarkStripeSet::ZMarkStripeSet() :
    _nstripes(0),
    _nstripes_mask(0),
    _stripes() {}

void ZMarkStripeSet::set_nstripes(size_t nstripes) {
  assert(is_power_of_2(nstripes), "Must be a power of two");
  assert(is_power_of_2(ZMarkStripesMax), "Must be a power of two");
  assert(nstripes >= 1, "Invalid number of stripes");
  assert(nstripes <= ZMarkStripesMax, "Invalid number of stripes");

  _nstripes = nstripes;
  _nstripes_mask = nstripes - 1;

  log_debug(gc, marking)("Using " SIZE_FORMAT " mark stripes", _nstripes);
}

bool ZMarkStripeSet::is_empty() const {
  for (size_t i = 0; i < _nstripes; i++) {
    if (!_stripes[i].is_empty()) {
      return false;
    }
  }

  return true;
}

ZMarkStripe* ZMarkStripeSet::stripe_for_worker(uint nworkers, uint worker_id) {
  const size_t spillover_limit = (nworkers / _nstripes) * _nstripes;
  size_t index;

  if (worker_id < spillover_limit) {
    // Not a spillover worker, use natural stripe
    index = worker_id & _nstripes_mask;
  } else {
    // Distribute spillover workers evenly across stripes
    const size_t spillover_nworkers = nworkers - spillover_limit;
    const size_t spillover_worker_id = worker_id - spillover_limit;
    const double spillover_chunk = (double)_nstripes / (double)spillover_nworkers;
    index = spillover_worker_id * spillover_chunk;
  }

  assert(index < _nstripes, "Invalid index");
  return &_stripes[index];
}

ZMarkThreadLocalStacks::ZMarkThreadLocalStacks() :
    _magazine(NULL) {
  for (size_t i = 0; i < ZMarkStripesMax; i++) {
    _stacks[i] = NULL;
  }
}

bool ZMarkThreadLocalStacks::is_empty(const ZMarkStripeSet* stripes) const {
  for (size_t i = 0; i < stripes->nstripes(); i++) {
    ZMarkStack* const stack = _stacks[i];
    if (stack != NULL) {
      return false;
    }
  }

  return true;
}

ZMarkStack* ZMarkThreadLocalStacks::allocate_stack(ZMarkStackAllocator* allocator) {
  if (_magazine == NULL) {
    // Allocate new magazine
    _magazine = allocator->alloc_magazine();
    if (_magazine == NULL) {
      return NULL;
    }
  }

  ZMarkStack* stack = NULL;

  if (!_magazine->pop(stack)) {
    // Magazine is empty, convert magazine into a new stack
    _magazine->~ZMarkStackMagazine();
    stack = new ((void*)_magazine) ZMarkStack();
    _magazine = NULL;
  }

  return stack;
}

void ZMarkThreadLocalStacks::free_stack(ZMarkStackAllocator* allocator, ZMarkStack* stack) {
  for (;;) {
    if (_magazine == NULL) {
      // Convert stack into a new magazine
      stack->~ZMarkStack();
      _magazine = new ((void*)stack) ZMarkStackMagazine();
      return;
    }

    if (_magazine->push(stack)) {
      // Success
      return;
    }

    // Free and uninstall full magazine
    allocator->free_magazine(_magazine);
    _magazine = NULL;
  }
}

bool ZMarkThreadLocalStacks::push_slow(ZMarkStackAllocator* allocator,
                                       ZMarkStripe* stripe,
                                       ZMarkStack** stackp,
                                       ZMarkStackEntry entry,
                                       bool publish) {
  ZMarkStack* stack = *stackp;

  for (;;) {
    if (stack == NULL) {
      // Allocate and install new stack
      *stackp = stack = allocate_stack(allocator);
      if (stack == NULL) {
        // Out of mark stack memory
        return false;
      }
    }

    if (stack->push(entry)) {
      // Success
      return true;
    }

    // Publish/Overflow and uninstall stack
    stripe->publish_stack(stack, publish);
    *stackp = stack = NULL;
  }
}

bool ZMarkThreadLocalStacks::pop_slow(ZMarkStackAllocator* allocator,
                                      ZMarkStripe* stripe,
                                      ZMarkStack** stackp,
                                      ZMarkStackEntry& entry) {
  ZMarkStack* stack = *stackp;

  for (;;) {
    if (stack == NULL) {
      // Try steal and install stack
      *stackp = stack = stripe->steal_stack();
      if (stack == NULL) {
        // Nothing to steal
        return false;
      }
    }

    if (stack->pop(entry)) {
      // Success
      return true;
    }

    // Free and uninstall stack
    free_stack(allocator, stack);
    *stackp = stack = NULL;
  }
}

bool ZMarkThreadLocalStacks::flush(ZMarkStackAllocator* allocator, ZMarkStripeSet* stripes) {
  bool flushed = false;

  // Flush all stacks
  for (size_t i = 0; i < stripes->nstripes(); i++) {
    ZMarkStripe* const stripe = stripes->stripe_at(i);
    ZMarkStack** const stackp = &_stacks[i];
    ZMarkStack* const stack = *stackp;
    if (stack == NULL) {
      continue;
    }

    // Free/Publish and uninstall stack
    if (stack->is_empty()) {
      free_stack(allocator, stack);
    } else {
      stripe->publish_stack(stack);
      flushed = true;
    }
    *stackp = NULL;
  }

  return flushed;
}

void ZMarkThreadLocalStacks::free(ZMarkStackAllocator* allocator) {
  // Free and uninstall magazine
  if (_magazine != NULL) {
    allocator->free_magazine(_magazine);
    _magazine = NULL;
  }
}