1 /*
   2  * Copyright (c) 2013, 2015, 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 "gc/g1/g1RemSet.hpp"
  30 #include "runtime/atomic.inline.hpp"
  31 
  32 G1HotCardCache::G1HotCardCache(G1CollectedHeap *g1h):
  33   _g1h(g1h), _hot_cache(NULL), _use_cache(false), _card_counts(g1h) {}
  34 
  35 void G1HotCardCache::initialize(G1RegionToSpaceMapper* card_counts_storage) {
  36   if (default_use_cache()) {
  37     _use_cache = true;
  38 
  39     _hot_cache_size = (size_t)1 << G1ConcRSLogCacheSize;
  40     _hot_cache = _hot_cache_memory.allocate(_hot_cache_size);
  41 
  42     reset_hot_cache_internal();
  43 
  44     // For refining the cards in the hot cache in parallel
  45     _hot_cache_par_chunk_size = ClaimChunkSize;
  46     _hot_cache_par_claimed_idx = 0;
  47 
  48     _card_counts.initialize(card_counts_storage);
  49   }
  50 }
  51 
  52 G1HotCardCache::~G1HotCardCache() {
  53   if (default_use_cache()) {
  54     assert(_hot_cache != NULL, "Logic");
  55     _hot_cache_memory.free();
  56     _hot_cache = NULL;
  57   }
  58 }
  59 
  60 jbyte* G1HotCardCache::insert(jbyte* card_ptr) {
  61   uint count = _card_counts.add_card_count(card_ptr);
  62   if (!_card_counts.is_hot(count)) {
  63     // The card is not hot so do not store it in the cache;
  64     // return it for immediate refining.
  65     return card_ptr;
  66   }
  67   // Otherwise, the card is hot.
  68   size_t index = Atomic::add(1, &_hot_cache_idx) - 1;
  69   size_t masked_index = index & (_hot_cache_size - 1);
  70   jbyte* current_ptr = _hot_cache[masked_index];
  71 
  72   // Try to store the new card pointer into the cache. Compare-and-swap to guard
  73   // against the unlikely event of a race resulting in another card pointer to
  74   // have already been written to the cache. In this case we will return
  75   // card_ptr in favor of the other option, which would be starting over. This
  76   // should be OK since card_ptr will likely be the older card already when/if
  77   // this ever happens.
  78   jbyte* previous_ptr = (jbyte*)Atomic::cmpxchg_ptr(card_ptr,
  79                                                     &_hot_cache[masked_index],
  80                                                     current_ptr);
  81   return (previous_ptr == current_ptr) ? previous_ptr : card_ptr;
  82 }
  83 
  84 void G1HotCardCache::drain(uint worker_i,
  85                            G1RemSet* g1rs,
  86                            DirtyCardQueue* into_cset_dcq) {
  87   if (!default_use_cache()) {
  88     assert(_hot_cache == NULL, "Logic");
  89     return;
  90   }
  91 
  92   assert(_hot_cache != NULL, "Logic");
  93   assert(!use_cache(), "cache should be disabled");
  94 
  95   while (_hot_cache_par_claimed_idx < _hot_cache_size) {
  96     size_t end_idx = Atomic::add(_hot_cache_par_chunk_size,
  97                                  &_hot_cache_par_claimed_idx);
  98     size_t start_idx = end_idx - _hot_cache_par_chunk_size;
  99     // The current worker has successfully claimed the chunk [start_idx..end_idx)
 100     end_idx = MIN2(end_idx, _hot_cache_size);
 101     for (size_t i = start_idx; i < end_idx; i++) {
 102       jbyte* card_ptr = _hot_cache[i];
 103       if (card_ptr != NULL) {
 104         if (g1rs->refine_card(card_ptr, worker_i, true)) {
 105           // The part of the heap spanned by the card contains references
 106           // that point into the current collection set.
 107           // We need to record the card pointer in the DirtyCardQueueSet
 108           // that we use for such cards.
 109           //
 110           // The only time we care about recording cards that contain
 111           // references that point into the collection set is during
 112           // RSet updating while within an evacuation pause.
 113           // In this case worker_i should be the id of a GC worker thread
 114           assert(SafepointSynchronize::is_at_safepoint(), "Should be at a safepoint");
 115           assert(worker_i < ParallelGCThreads,
 116                  err_msg("incorrect worker id: %u", worker_i));
 117 
 118           into_cset_dcq->enqueue(card_ptr);
 119         }
 120       } else {
 121         break;
 122       }
 123     }
 124   }
 125 
 126   // The existing entries in the hot card cache, which were just refined
 127   // above, are discarded prior to re-enabling the cache near the end of the GC.
 128 }
 129 
 130 void G1HotCardCache::reset_card_counts(HeapRegion* hr) {
 131   _card_counts.clear_region(hr);
 132 }
 133 
 134 void G1HotCardCache::reset_card_counts() {
 135   _card_counts.clear_all();
 136 }