Mercurial > hg > truffle
diff src/share/vm/gc_implementation/concurrentMarkSweep/promotionInfo.hpp @ 1546:a00b51b2dda4
6948539: CMS+UseCompressedOops: placement of cms_free bit interferes with promoted object link
Summary: When using compressed oops, use compressed promoted pointers in b63:b31 of the mark word, so as not to interfere with the CMS "freeness bit" at b7. Updated mark-word layout documentation.
Reviewed-by: minqi, poonam, jmasa, coleenp
author | ysr |
---|---|
date | Mon, 17 May 2010 00:47:28 -0700 |
parents | a8127dc669ba |
children | c18cbe5936b8 |
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--- a/src/share/vm/gc_implementation/concurrentMarkSweep/promotionInfo.hpp Fri May 14 10:28:46 2010 -0700 +++ b/src/share/vm/gc_implementation/concurrentMarkSweep/promotionInfo.hpp Mon May 17 00:47:28 2010 -0700 @@ -1,5 +1,5 @@ /* - * Copyright 2001-2009 Sun Microsystems, Inc. All Rights Reserved. + * Copyright 2010 Sun Microsystems, Inc. All Rights Reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it @@ -32,30 +32,75 @@ displaced_mark = nth_bit(2), // i.e. 0x4 next_mask = ~(right_n_bits(3)) // i.e. ~(0x7) }; - intptr_t _next; + + // Below, we want _narrow_next in the "higher" 32 bit slot, + // whose position will depend on endian-ness of the platform. + // This is so that there is no interference with the + // cms_free_bit occupying bit position 7 (lsb == 0) + // when we are using compressed oops; see FreeChunk::isFree(). + // We cannot move the cms_free_bit down because currently + // biased locking code assumes that age bits are contiguous + // with the lock bits. Even if that assumption were relaxed, + // the least position we could move this bit to would be + // to bit position 3, which would require 16 byte alignment. + typedef struct { +#ifdef VM_LITTLE_ENDIAN + LP64_ONLY(narrowOop _pad;) + narrowOop _narrow_next; +#else + narrowOop _narrow_next; + LP64_ONLY(narrowOop _pad;) +#endif + } Data; + + union { + intptr_t _next; + Data _data; + }; public: inline PromotedObject* next() const { - return (PromotedObject*)(_next & next_mask); + assert(!((FreeChunk*)this)->isFree(), "Error"); + PromotedObject* res; + if (UseCompressedOops) { + // The next pointer is a compressed oop stored in the top 32 bits + res = (PromotedObject*)oopDesc::decode_heap_oop(_data._narrow_next); + } else { + res = (PromotedObject*)(_next & next_mask); + } + assert(oop(res)->is_oop_or_null(true /* ignore mark word */), "Not an oop?"); + return res; } inline void setNext(PromotedObject* x) { - assert(((intptr_t)x & ~next_mask) == 0, - "Conflict in bit usage, " - " or insufficient alignment of objects"); - _next |= (intptr_t)x; + assert(((intptr_t)x & ~next_mask) == 0, "Conflict in bit usage, " + "or insufficient alignment of objects"); + if (UseCompressedOops) { + assert(_data._narrow_next == 0, "Overwrite?"); + _data._narrow_next = oopDesc::encode_heap_oop(oop(x)); + } else { + _next |= (intptr_t)x; + } + assert(!((FreeChunk*)this)->isFree(), "Error"); } inline void setPromotedMark() { _next |= promoted_mask; + assert(!((FreeChunk*)this)->isFree(), "Error"); } inline bool hasPromotedMark() const { + assert(!((FreeChunk*)this)->isFree(), "Error"); return (_next & promoted_mask) == promoted_mask; } inline void setDisplacedMark() { _next |= displaced_mark; + assert(!((FreeChunk*)this)->isFree(), "Error"); } inline bool hasDisplacedMark() const { + assert(!((FreeChunk*)this)->isFree(), "Error"); return (_next & displaced_mark) != 0; } - inline void clearNext() { _next = 0; } + inline void clearNext() { + _next = 0; + assert(!((FreeChunk*)this)->isFree(), "Error"); + } debug_only(void *next_addr() { return (void *) &_next; }) };