Fri, 10 Oct 2014 15:51:58 +0200
8059758: Footprint regressions with JDK-8038423
Summary: Changes in JDK-8038423 always initialize (zero out) virtual memory used for auxiliary data structures. This causes a footprint regression for G1 in startup benchmarks. This is because they do not touch that memory at all, so the operating system does not actually commit these pages. The fix is to, if the initialization value of the data structures matches the default value of just committed memory (=0), do not do anything.
Reviewed-by: jwilhelm, brutisso
1 /*
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25 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1HOTCARDCACHE_HPP
26 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1HOTCARDCACHE_HPP
28 #include "gc_implementation/g1/g1_globals.hpp"
29 #include "gc_implementation/g1/g1CardCounts.hpp"
30 #include "memory/allocation.hpp"
31 #include "runtime/safepoint.hpp"
32 #include "runtime/thread.inline.hpp"
33 #include "utilities/globalDefinitions.hpp"
35 class DirtyCardQueue;
36 class G1CollectedHeap;
37 class G1RemSet;
38 class HeapRegion;
40 // An evicting cache of cards that have been logged by the G1 post
41 // write barrier. Placing a card in the cache delays the refinement
42 // of the card until the card is evicted, or the cache is drained
43 // during the next evacuation pause.
44 //
45 // The first thing the G1 post write barrier does is to check whether
46 // the card containing the updated pointer is already dirty and, if
47 // so, skips the remaining code in the barrier.
48 //
49 // Delaying the refinement of a card will make the card fail the
50 // first is_dirty check in the write barrier, skipping the remainder
51 // of the write barrier.
52 //
53 // This can significantly reduce the overhead of the write barrier
54 // code, increasing throughput.
56 class G1HotCardCache: public CHeapObj<mtGC> {
57 G1CollectedHeap* _g1h;
59 // The card cache table
60 jbyte** _hot_cache;
62 int _hot_cache_size;
63 int _n_hot;
64 int _hot_cache_idx;
66 int _hot_cache_par_chunk_size;
67 volatile int _hot_cache_par_claimed_idx;
69 bool _use_cache;
71 G1CardCounts _card_counts;
73 bool default_use_cache() const {
74 return (G1ConcRSLogCacheSize > 0);
75 }
77 public:
78 G1HotCardCache(G1CollectedHeap* g1h);
79 ~G1HotCardCache();
81 void initialize(G1RegionToSpaceMapper* card_counts_storage);
83 bool use_cache() { return _use_cache; }
85 void set_use_cache(bool b) {
86 _use_cache = (b ? default_use_cache() : false);
87 }
89 // Returns the card to be refined or NULL.
90 //
91 // Increments the count for given the card. if the card is not 'hot',
92 // it is returned for immediate refining. Otherwise the card is
93 // added to the hot card cache.
94 // If there is enough room in the hot card cache for the card we're
95 // adding, NULL is returned and no further action in needed.
96 // If we evict a card from the cache to make room for the new card,
97 // the evicted card is then returned for refinement.
98 jbyte* insert(jbyte* card_ptr);
100 // Refine the cards that have delayed as a result of
101 // being in the cache.
102 void drain(uint worker_i, G1RemSet* g1rs, DirtyCardQueue* into_cset_dcq);
104 // Set up for parallel processing of the cards in the hot cache
105 void reset_hot_cache_claimed_index() {
106 _hot_cache_par_claimed_idx = 0;
107 }
109 // Resets the hot card cache and discards the entries.
110 void reset_hot_cache() {
111 assert(SafepointSynchronize::is_at_safepoint(), "Should be at a safepoint");
112 assert(Thread::current()->is_VM_thread(), "Current thread should be the VMthread");
113 _hot_cache_idx = 0; _n_hot = 0;
114 }
116 bool hot_cache_is_empty() { return _n_hot == 0; }
118 // Zeros the values in the card counts table for entire committed heap
119 void reset_card_counts();
121 // Zeros the values in the card counts table for the given region
122 void reset_card_counts(HeapRegion* hr);
123 };
125 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1HOTCARDCACHE_HPP