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