1 /*
   2  * Copyright (c) 2013, 2017, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "gc/g1/dirtyCardQueue.hpp"
  27 #include "gc/g1/g1CollectedHeap.inline.hpp"
  28 #include "gc/g1/g1HotCardCache.hpp"
  29 #include "runtime/atomic.hpp"
  30 
  31 G1HotCardCache::G1HotCardCache(G1CollectedHeap *g1h):
  32   _g1h(g1h), _hot_cache(NULL), _use_cache(false), _card_counts(g1h) {}
  33 
  34 void G1HotCardCache::initialize(G1RegionToSpaceMapper* card_counts_storage) {
  35   if (default_use_cache()) {
  36     _use_cache = true;
  37 
  38     _hot_cache_size = (size_t)1 << G1ConcRSLogCacheSize;
  39     _hot_cache = ArrayAllocator<jbyte*>::allocate(_hot_cache_size, mtGC);
  40 
  41     reset_hot_cache_internal();
  42 
  43     // For refining the cards in the hot cache in parallel
  44     _hot_cache_par_chunk_size = ClaimChunkSize;
  45     _hot_cache_par_claimed_idx = 0;
  46 
  47     _card_counts.initialize(card_counts_storage);
  48   }
  49 }
  50 
  51 G1HotCardCache::~G1HotCardCache() {
  52   if (default_use_cache()) {
  53     assert(_hot_cache != NULL, "Logic");
  54     ArrayAllocator<jbyte*>::free(_hot_cache, _hot_cache_size);
  55     _hot_cache = NULL;
  56   }
  57 }
  58 
  59 jbyte* G1HotCardCache::insert(jbyte* card_ptr) {
  60   uint count = _card_counts.add_card_count(card_ptr);
  61   if (!_card_counts.is_hot(count)) {
  62     // The card is not hot so do not store it in the cache;
  63     // return it for immediate refining.
  64     return card_ptr;
  65   }
  66   // Otherwise, the card is hot.
  67   size_t index = Atomic::add(1u, &_hot_cache_idx) - 1;
  68   size_t masked_index = index & (_hot_cache_size - 1);
  69   jbyte* current_ptr = _hot_cache[masked_index];
  70 
  71   // Try to store the new card pointer into the cache. Compare-and-swap to guard
  72   // against the unlikely event of a race resulting in another card pointer to
  73   // have already been written to the cache. In this case we will return
  74   // card_ptr in favor of the other option, which would be starting over. This
  75   // should be OK since card_ptr will likely be the older card already when/if
  76   // this ever happens.
  77   jbyte* previous_ptr = Atomic::cmpxchg(card_ptr,
  78                                         &_hot_cache[masked_index],
  79                                         current_ptr);
  80   return (previous_ptr == current_ptr) ? previous_ptr : card_ptr;
  81 }
  82 
  83 void G1HotCardCache::drain(CardTableEntryClosure* cl, uint worker_i) {
  84   assert(default_use_cache(), "Drain only necessary if we use the hot card cache.");
  85 
  86   assert(_hot_cache != NULL, "Logic");
  87   assert(!use_cache(), "cache should be disabled");
  88 
  89   while (_hot_cache_par_claimed_idx < _hot_cache_size) {
  90     size_t end_idx = Atomic::add(_hot_cache_par_chunk_size,
  91                                  &_hot_cache_par_claimed_idx);
  92     size_t start_idx = end_idx - _hot_cache_par_chunk_size;
  93     // The current worker has successfully claimed the chunk [start_idx..end_idx)
  94     end_idx = MIN2(end_idx, _hot_cache_size);
  95     for (size_t i = start_idx; i < end_idx; i++) {
  96       jbyte* card_ptr = _hot_cache[i];
  97       if (card_ptr != NULL) {
  98         bool result = cl->do_card_ptr(card_ptr, worker_i);
  99         assert(result, "Closure should always return true");
 100       } else {
 101         break;
 102       }
 103     }
 104   }
 105 
 106   // The existing entries in the hot card cache, which were just refined
 107   // above, are discarded prior to re-enabling the cache near the end of the GC.
 108 }
 109 
 110 void G1HotCardCache::reset_card_counts(HeapRegion* hr) {
 111   _card_counts.clear_region(hr);
 112 }
 113 
 114 void G1HotCardCache::reset_card_counts() {
 115   _card_counts.clear_all();
 116 }