The College of Engineering at the University of Utahcs4400/malloc-2.pdf · 2018. 11. 29. ·...

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Utilization

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Throughput

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p2 = malloc(1) 21 2 31 3 30 3 31 3 40 4 01

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p2 = malloc(1) 21 2 31 3 30 3 31 3 40 4 01

p4 = malloc(4)

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p2 = malloc(1) 21 2 60 6 31 3 41 4 01

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p2 = malloc(1) 21 2 60 6 31 3 41 4 01

p4 = malloc(4) 21 2 61 6 31 3 41 4 01

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while (GET_SIZE(HDRP(bp)) != 0) { if (!GET_ALLOC(HDRP(bp)) && (GET_SIZE(HDRP(bp)) >= new_size)) { set_allocated(bp, new_size); return bp; } bp = NEXT_BLKP(bp);}

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void *best_bp = NULL; while (GET_SIZE(HDRP(bp)) != 0) { if (!GET_ALLOC(HDRP(bp)) && (GET_SIZE(HDRP(bp)) >= new_size)) { if (!best_bp || (GET_SIZE(HDRP(bp)) < GET_SIZE(HDRP(best_bp)))) best_bp = bp; } bp = NEXT_BLKP(bp);}if (best_bp) { set_allocated(best_bp, new_size); return best_bp;}

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p = mm_malloc(8);memset(p, 0, 8);

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typedef struct { size_t size; char allocated;} block_header;

typedef struct { size_t size; int filler;} block_footer;

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typedef size_t block_header; typedef size_t block_footer;

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typedef size_t block_header; typedef size_t block_footer;

#define GET(p) (*(size_t *)(p)) #define GET_ALLOC(p) (GET(p) & 0x1)#define GET_SIZE(p) (GET(p) & ~0xF)

#define PUT(p, val) (*(size_t *)(p) = (val)) #define PACK(size, alloc) ((size) | (alloc))

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#include #include #define GET(p) (*(size_t *)(p))#define PUT(p, val) (*(size_t *)(p) = (val)) #define GET_ALLOC(p) (GET(p) & 0x1)#define GET_SIZE(p) (GET(p) & ~0xF) #define PACK(size, alloc) ((size) | (alloc)) int main() { void *p = malloc(sizeof(size_t)); PUT(p, PACK(48, 1)); printf("%ld %s\n", GET_SIZE(p), (GET_ALLOC(p) ? "alloc" : "unalloc"));}

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typedef int block_header;typedef int block_footer;#define GET(p) (*(int *)(p))#define PUT(p, val) (*(int *)(p) = (val))

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21 2 60 6 31 3 41 4 01

��previous��

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free(p2)�⇒��PREV_BLKP

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free(p3)�⇒��PREV_BLKP

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first_bp

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free_listfirst_bp

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free(p3)free_listfirst_bp

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free_listfirst_bp

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free_listfirst_bp

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free(p4)

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free_listfirst_bp

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free(p4)

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free_listfirst_bp

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free(p4)

free_listfirst_bp

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free_listfirst_bp

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free(p4)

free_listfirst_bp

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free_listfirst_bp

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free(p4)

free_listfirst_bp

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free_listfirst_bp

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free(p4)

free_listfirst_bp

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typedef struct list_node { struct list_node *prev; struct list_node *next;} list_node; .... void *mm_malloc(size_t size) { int need_size = max(size, sizeof(list_node)); int new_size = ALIGN(need_size + OVERHEAD); ....}

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void *coalesce(void *bp) { .... if (prev_alloc && next_alloc) { /* Case 1 */ add_to_free_list((list_node *)bp); } ....}

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free_lists

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free_lists

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free_tree

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free_listfirst_chunk

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� ��free��Based on the address: the allocator keeps a mapping ofaddress ranges to block sizes

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Through a free list or chunk-specific bitmap

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Any unallocated block will work within a chunk that holds theblock size

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Block sizes must be rounded up to match some chunk’scontent

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When no chunk for the block size has any unallocatedblocks

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The College of Engineering at the University of Utahcs4400/malloc-2.pdf · 2018. 11. 29. ·...

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