1 /*
   2  * Copyright (c) 2013, 2019, 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/g1CardTableEntryClosure.hpp"
  27 #include "gc/g1/g1CollectedHeap.inline.hpp"
  28 #include "gc/g1/g1DirtyCardQueue.hpp"
  29 #include "gc/g1/g1HotCardCache.hpp"
  30 #include "runtime/atomic.hpp"
  31 
  32 G1HotCardCache::G1HotCardCache(G1CollectedHeap *g1h):
  33   _g1h(g1h), _use_cache(false), _card_counts(g1h),
  34   _hot_cache(NULL), _hot_cache_size(0), _hot_cache_par_chunk_size(0),
  35   _hot_cache_idx(0), _hot_cache_par_claimed_idx(0)
  36 {}
  37 
  38 void G1HotCardCache::initialize(G1RegionToSpaceMapper* card_counts_storage) {
  39   if (default_use_cache()) {
  40     _use_cache = true;
  41 
  42     _hot_cache_size = (size_t)1 << G1ConcRSLogCacheSize;
  43     _hot_cache = ArrayAllocator<CardValue*>::allocate(_hot_cache_size, mtGC);
  44 
  45     reset_hot_cache_internal();
  46 
  47     // For refining the cards in the hot cache in parallel
  48     _hot_cache_par_chunk_size = ClaimChunkSize;
  49     _hot_cache_par_claimed_idx = 0;
  50 
  51     _card_counts.initialize(card_counts_storage);
  52   }
  53 }
  54 
  55 G1HotCardCache::~G1HotCardCache() {
  56   if (default_use_cache()) {
  57     assert(_hot_cache != NULL, "Logic");
  58     ArrayAllocator<CardValue*>::free(_hot_cache, _hot_cache_size);
  59     _hot_cache = NULL;
  60   }
  61 }
  62 
  63 CardTable::CardValue* G1HotCardCache::insert(CardValue* card_ptr) {
  64   uint count = _card_counts.add_card_count(card_ptr);
  65   if (!_card_counts.is_hot(count)) {
  66     // The card is not hot so do not store it in the cache;
  67     // return it for immediate refining.
  68     return card_ptr;
  69   }
  70   // Otherwise, the card is hot.
  71   size_t index = Atomic::add(&_hot_cache_idx, 1u) - 1;
  72   size_t masked_index = index & (_hot_cache_size - 1);
  73   CardValue* current_ptr = _hot_cache[masked_index];
  74 
  75   // Try to store the new card pointer into the cache. Compare-and-swap to guard
  76   // against the unlikely event of a race resulting in another card pointer to
  77   // have already been written to the cache. In this case we will return
  78   // card_ptr in favor of the other option, which would be starting over. This
  79   // should be OK since card_ptr will likely be the older card already when/if
  80   // this ever happens.
  81   CardValue* previous_ptr = Atomic::cmpxchg(card_ptr,
  82                                             &_hot_cache[masked_index],
  83                                             current_ptr);
  84   return (previous_ptr == current_ptr) ? previous_ptr : card_ptr;
  85 }
  86 
  87 void G1HotCardCache::drain(G1CardTableEntryClosure* cl, uint worker_id) {
  88   assert(default_use_cache(), "Drain only necessary if we use the hot card cache.");
  89 
  90   assert(_hot_cache != NULL, "Logic");
  91   assert(!use_cache(), "cache should be disabled");
  92 
  93   while (_hot_cache_par_claimed_idx < _hot_cache_size) {
  94     size_t end_idx = Atomic::add(&_hot_cache_par_claimed_idx,
  95                                  _hot_cache_par_chunk_size);
  96     size_t start_idx = end_idx - _hot_cache_par_chunk_size;
  97     // The current worker has successfully claimed the chunk [start_idx..end_idx)
  98     end_idx = MIN2(end_idx, _hot_cache_size);
  99     for (size_t i = start_idx; i < end_idx; i++) {
 100       CardValue* card_ptr = _hot_cache[i];
 101       if (card_ptr != NULL) {
 102         cl->do_card_ptr(card_ptr, worker_id);
 103       } else {
 104         break;
 105       }
 106     }
 107   }
 108 
 109   // The existing entries in the hot card cache, which were just refined
 110   // above, are discarded prior to re-enabling the cache near the end of the GC.
 111 }
 112 
 113 void G1HotCardCache::reset_card_counts(HeapRegion* hr) {
 114   _card_counts.clear_region(hr);
 115 }
--- EOF ---