src/hotspot/share/gc/z/zLiveMap.cpp
author pliden
Tue, 12 Jun 2018 17:40:28 +0200
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child 50875 2217b2fc29ea
permissions -rw-r--r--
8204210: Implementation: JEP 333: ZGC: A Scalable Low-Latency Garbage Collector (Experimental) Reviewed-by: pliden, stefank, eosterlund, ehelin, sjohanss, rbackman, coleenp, ihse, jgeorge, lmesnik, rkennke Contributed-by: per.liden@oracle.com, stefan.karlsson@oracle.com, erik.osterlund@oracle.com, mikael.gerdin@oracle.com, kim.barrett@oracle.com, nils.eliasson@oracle.com, rickard.backman@oracle.com, rwestrel@redhat.com, coleen.phillimore@oracle.com, robbin.ehn@oracle.com, gerard.ziemski@oracle.com, hugh.wilkinson@intel.com, sandhya.viswanathan@intel.com, bill.npo.wheeler@intel.com, vinay.k.awasthi@intel.com, yasuenag@gmail.com
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/*
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 * Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 *
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 * This code is free software; you can redistribute it and/or modify it
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 * under the terms of the GNU General Public License version 2 only, as
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 * published by the Free Software Foundation.
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 *
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * version 2 for more details (a copy is included in the LICENSE file that
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 * accompanied this code).
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 *
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 * You should have received a copy of the GNU General Public License version
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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 *
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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * or visit www.oracle.com if you need additional information or have any
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 * questions.
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 */
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#include "precompiled.hpp"
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#include "gc/z/zHeap.inline.hpp"
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#include "gc/z/zLiveMap.inline.hpp"
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#include "gc/z/zStat.hpp"
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#include "gc/z/zThread.hpp"
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#include "logging/log.hpp"
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#include "runtime/atomic.hpp"
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#include "runtime/orderAccess.hpp"
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#include "utilities/debug.hpp"
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static const ZStatCounter ZCounterMarkSeqNumResetContention("Contention", "Mark SeqNum Reset Contention", ZStatUnitOpsPerSecond);
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static const ZStatCounter ZCounterMarkSegmentResetContention("Contention", "Mark Segment Reset Contention", ZStatUnitOpsPerSecond);
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ZLiveMap::ZLiveMap(uint32_t size) :
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    _seqnum(0),
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    _live_objects(0),
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    _live_bytes(0),
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    _segment_live_bits(0),
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    _segment_claim_bits(0),
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    // We need at least one bit per segment.
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    _bitmap(MAX2<size_t>(size, nsegments) * 2),
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    _shift(exact_log2(segment_size())) {}
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void ZLiveMap::reset(size_t index) {
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  const uint32_t seqnum_initializing = (uint32_t)-1;
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  bool contention = false;
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  // Multiple threads can enter here, make sure only one of them
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  // resets the marking information while the others busy wait.
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  for (uint32_t seqnum = _seqnum; seqnum != ZGlobalSeqNum; seqnum = _seqnum) {
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    if ((seqnum != seqnum_initializing) &&
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        (Atomic::cmpxchg(seqnum_initializing, &_seqnum, seqnum) == seqnum)) {
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      // Reset marking information
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      _live_bytes = 0;
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      _live_objects = 0;
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      // Clear segment claimed/live bits
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      segment_live_bits().clear();
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      segment_claim_bits().clear();
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      // Make sure the newly reset marking information is
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      // globally visible before updating the page seqnum.
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      OrderAccess::storestore();
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      // Update seqnum
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      assert(_seqnum == seqnum_initializing, "Invalid");
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      _seqnum = ZGlobalSeqNum;
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      break;
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    }
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    // Mark reset contention
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    if (!contention) {
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      // Count contention once, not every loop
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      ZStatInc(ZCounterMarkSeqNumResetContention);
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      contention = true;
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      log_trace(gc)("Mark seqnum reset contention, thread: " PTR_FORMAT " (%s), map: " PTR_FORMAT ", bit: " SIZE_FORMAT,
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                    ZThread::id(), ZThread::name(), p2i(this), index);
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    }
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  }
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}
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void ZLiveMap::reset_segment(BitMap::idx_t segment) {
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  bool contention = false;
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  if (!claim_segment(segment)) {
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    // Already claimed, wait for live bit to be set
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    while (!is_segment_live(segment)) {
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      // Busy wait. The loadload barrier is needed to make
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      // sure we re-read the live bit every time we loop.
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      OrderAccess::loadload();
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      // Mark reset contention
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      if (!contention) {
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        // Count contention once, not every loop
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        ZStatInc(ZCounterMarkSegmentResetContention);
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        contention = true;
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        log_trace(gc)("Mark segment reset contention, thread: " PTR_FORMAT " (%s), map: " PTR_FORMAT ", segment: " SIZE_FORMAT,
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                      ZThread::id(), ZThread::name(), p2i(this), segment);
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      }
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    }
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    // Segment is live
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    return;
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  }
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  // Segment claimed, clear it
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  const BitMap::idx_t start_index = segment_start(segment);
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  const BitMap::idx_t end_index   = segment_end(segment);
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  if (segment_size() / BitsPerWord >= 32) {
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    _bitmap.clear_large_range(start_index, end_index);
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  } else {
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    _bitmap.clear_range(start_index, end_index);
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  }
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  // Set live bit
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  const bool success = set_segment_live_atomic(segment);
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  assert(success, "Should never fail");
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}