Mercurial > hg > graal-jvmci-8
comparison src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp @ 1027:39b01ab7035a
6888898: CMS: ReduceInitialCardMarks unsafe in the presence of cms precleaning
6889757: G1: enable card mark elision for initializing writes from compiled code (ReduceInitialCardMarks)
Summary: Defer the (compiler-elided) card-mark upon a slow-path allocation until after the store and before the next subsequent safepoint; G1 now answers yes to can_elide_tlab_write_barriers().
Reviewed-by: jcoomes, kvn, never
author | ysr |
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date | Fri, 16 Oct 2009 02:05:46 -0700 |
parents | 2c79770d1f6e |
children | ed52bcc32739 |
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1025:1ee412f7fec9 | 1027:39b01ab7035a |
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990 virtual size_t unsafe_max_tlab_alloc(Thread* thr) const; | 990 virtual size_t unsafe_max_tlab_alloc(Thread* thr) const; |
991 virtual HeapWord* allocate_new_tlab(size_t size); | 991 virtual HeapWord* allocate_new_tlab(size_t size); |
992 | 992 |
993 // Can a compiler initialize a new object without store barriers? | 993 // Can a compiler initialize a new object without store barriers? |
994 // This permission only extends from the creation of a new object | 994 // This permission only extends from the creation of a new object |
995 // via a TLAB up to the first subsequent safepoint. | 995 // via a TLAB up to the first subsequent safepoint. If such permission |
996 // is granted for this heap type, the compiler promises to call | |
997 // defer_store_barrier() below on any slow path allocation of | |
998 // a new object for which such initializing store barriers will | |
999 // have been elided. G1, like CMS, allows this, but should be | |
1000 // ready to provide a compensating write barrier as necessary | |
1001 // if that storage came out of a non-young region. The efficiency | |
1002 // of this implementation depends crucially on being able to | |
1003 // answer very efficiently in constant time whether a piece of | |
1004 // storage in the heap comes from a young region or not. | |
1005 // See ReduceInitialCardMarks. | |
996 virtual bool can_elide_tlab_store_barriers() const { | 1006 virtual bool can_elide_tlab_store_barriers() const { |
997 // Since G1's TLAB's may, on occasion, come from non-young regions | 1007 return true; |
998 // as well. (Is there a flag controlling that? XXX) | 1008 } |
999 return false; | 1009 |
1010 bool is_in_young(oop obj) { | |
1011 HeapRegion* hr = heap_region_containing(obj); | |
1012 return hr != NULL && hr->is_young(); | |
1013 } | |
1014 | |
1015 // We don't need barriers for initializing stores to objects | |
1016 // in the young gen: for the SATB pre-barrier, there is no | |
1017 // pre-value that needs to be remembered; for the remembered-set | |
1018 // update logging post-barrier, we don't maintain remembered set | |
1019 // information for young gen objects. Note that non-generational | |
1020 // G1 does not have any "young" objects, should not elide | |
1021 // the rs logging barrier and so should always answer false below. | |
1022 // However, non-generational G1 (-XX:-G1Gen) appears to have | |
1023 // bit-rotted so was not tested below. | |
1024 virtual bool can_elide_initializing_store_barrier(oop new_obj) { | |
1025 assert(G1Gen || !is_in_young(new_obj), | |
1026 "Non-generational G1 should never return true below"); | |
1027 return is_in_young(new_obj); | |
1000 } | 1028 } |
1001 | 1029 |
1002 // Can a compiler elide a store barrier when it writes | 1030 // Can a compiler elide a store barrier when it writes |
1003 // a permanent oop into the heap? Applies when the compiler | 1031 // a permanent oop into the heap? Applies when the compiler |
1004 // is storing x to the heap, where x->is_perm() is true. | 1032 // is storing x to the heap, where x->is_perm() is true. |