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6687581: Make CMS work with compressed oops

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Make FreeChunk read markword instead of LSB in _klass pointer to indicate that it's a FreeChunk for compressed oops.

Reviewed-by: ysr, jmasa
This commit is contained in:
Coleen Phillimore 2008-06-09 11:51:19 -04:00
parent 4cce21039e
commit a2d6036a4d
13 changed files with 315 additions and 160 deletions
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82
hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/freeBlockDictionary.hpp
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@ -22,88 +22,6 @@
*
*/
//
// Free block maintenance for Concurrent Mark Sweep Generation
//
// The main data structure for free blocks are
// . an indexed array of small free blocks, and
// . a dictionary of large free blocks
//
// No virtuals in FreeChunk (don't want any vtables).
// A FreeChunk is merely a chunk that can be in a doubly linked list
// and has a size field. NOTE: FreeChunks are distinguished from allocated
// objects in two ways (by the sweeper). The second word (prev) has the
// LSB set to indicate a free chunk; allocated objects' klass() pointers
// don't have their LSB set. The corresponding bit in the CMSBitMap is
// set when the chunk is allocated. There are also blocks that "look free"
// but are not part of the free list and should not be coalesced into larger
// free blocks. These free blocks have their two LSB's set.
class FreeChunk VALUE_OBJ_CLASS_SPEC {
friend class VMStructs;
FreeChunk* _next;
FreeChunk* _prev;
size_t _size;
public:
NOT_PRODUCT(static const size_t header_size();)
// Returns "true" if the "wrd", which is required to be the second word
// of a block, indicates that the block represents a free chunk.
static bool secondWordIndicatesFreeChunk(intptr_t wrd) {
return (wrd & 0x1) == 0x1;
}
bool isFree() const {
return secondWordIndicatesFreeChunk((intptr_t)_prev);
}
bool cantCoalesce() const { return (((intptr_t)_prev) & 0x3) == 0x3; }
FreeChunk* next() const { return _next; }
FreeChunk* prev() const { return (FreeChunk*)(((intptr_t)_prev) & ~(0x3)); }
debug_only(void* prev_addr() const { return (void*)&_prev; })
void linkAfter(FreeChunk* ptr) {
linkNext(ptr);
if (ptr != NULL) ptr->linkPrev(this);
}
void linkAfterNonNull(FreeChunk* ptr) {
assert(ptr != NULL, "precondition violation");
linkNext(ptr);
ptr->linkPrev(this);
}
void linkNext(FreeChunk* ptr) { _next = ptr; }
void linkPrev(FreeChunk* ptr) { _prev = (FreeChunk*)((intptr_t)ptr | 0x1); }
void clearPrev() { _prev = NULL; }
void clearNext() { _next = NULL; }
void dontCoalesce() {
// the block should be free
assert(isFree(), "Should look like a free block");
_prev = (FreeChunk*)(((intptr_t)_prev) | 0x2);
}
void markFree() { _prev = (FreeChunk*)((intptr_t)_prev | 0x1); }
void markNotFree() { _prev = NULL; }
size_t size() const { return _size; }
void setSize(size_t size) { _size = size; }
// For volatile reads:
size_t* size_addr() { return &_size; }
// Return the address past the end of this chunk
HeapWord* end() const { return ((HeapWord*) this) + _size; }
// debugging
void verify() const PRODUCT_RETURN;
void verifyList() const PRODUCT_RETURN;
void mangleAllocated(size_t size) PRODUCT_RETURN;
void mangleFreed(size_t size) PRODUCT_RETURN;
};
// Alignment helpers etc.
#define numQuanta(x,y) ((x+y-1)/y)
enum AlignmentConstants {
MinChunkSize = numQuanta(sizeof(FreeChunk), MinObjAlignmentInBytes) * MinObjAlignment
};
// A FreeBlockDictionary is an abstract superclass that will allow
// a number of alternative implementations in the future.