1 /* -----------------------------------------------------------------------------
3 * (c) The GHC Team, 1998-1999
5 * MegaBlock Allocator interface.
7 * ---------------------------------------------------------------------------*/
12 extern lnat RTS_VAR(mblocks_allocated);
14 extern void * getMBlock(void);
15 extern void * getMBlocks(nat n);
18 /* ToDo: Perhaps by adjusting this value we can make linking without
19 * -static work (i.e., not generate a core-dumping executable)? */
20 #if SIZEOF_VOID_P == 8
21 #define HEAP_BASE 0x180000000L
23 #error I have no idea where to begin the heap on a non-64-bit osf3 machine.
28 // we're using the generic method
33 /* -----------------------------------------------------------------------------
34 The HEAP_ALLOCED() test.
36 HEAP_ALLOCED is called FOR EVERY SINGLE CLOSURE during GC.
39 Implementation of HEAP_ALLOCED
40 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
42 Since heap is allocated in chunks of megablocks (MBLOCK_SIZE), we
43 can just use a table to record which megablocks in the address
44 space belong to the heap. On a 32-bit machine, with 1Mb
45 megablocks, using 8 bits for each entry in the table, the table
46 requires 4k. Lookups during GC will be fast, because the table
47 will be quickly cached (indeed, performance measurements showed no
48 measurable difference between doing the table lookup and using a
51 On 64-bit machines, we cache one 12-bit block map that describes
52 4096 megablocks or 4GB of memory. If HEAP_ALLOCED is called for
53 an address that is not in the cache, it calls slowIsHeapAlloced
54 (see MBlock.c) which will find the block map for the 4GB block in
56 -------------------------------------------------------------------------- */
58 #if SIZEOF_VOID_P == 4
59 extern StgWord8 mblock_map[];
61 /* On a 32-bit machine a 4KB table is always sufficient */
62 # define MBLOCK_MAP_SIZE 4096
63 # define MBLOCK_MAP_ENTRY(p) ((StgWord)(p) >> MBLOCK_SHIFT)
64 # define HEAP_ALLOCED(p) mblock_map[MBLOCK_MAP_ENTRY(p)]
66 #elif SIZEOF_VOID_P == 8
68 # define MBLOCK_MAP_SIZE 4096
69 # define MBLOCK_MAP_ENTRY(p) (((StgWord)(p) & 0xffffffff) >> MBLOCK_SHIFT)
73 StgWord8 mblocks[MBLOCK_MAP_SIZE];
76 extern MBlockMap *mblock_cache;
78 StgBool slowIsHeapAlloced(void *p);
80 # define HEAP_ALLOCED(p) \
81 ( ((((StgWord)(p)) >> 32) == mblock_cache->addrHigh32) \
82 ? mblock_cache->mblocks[MBLOCK_MAP_ENTRY(p)] \
83 : slowIsHeapAlloced(p) )
86 # error HEAP_ALLOCED not defined
89 #endif /* __MBLOCK_H__ */