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mm.c
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/*
* mm.c
*
* Simple allocator based on implicit free lists with boundary
* tag coalescing. Each block has header and footer of the form:
*
* 31 3 2 1 0
* -----------------------------------
* | s s s s ... s s s 0 0 a/f
* -----------------------------------
*
* where s are the meaningful size bits and a/f is set
* if the block is allocated. The list has the following form:
*
* begin end
* heap heap
* -----------------------------------------------------------------
* | pad | | | | | | | | | | | | zero or more usr blks | hdr(0:a) |
* -----------------------------------------------------------------
* | seglist | | epilogue |
* | roots | | block |
*
* The allocated prologue and epilogue blocks are overhead that
* eliminate edge conditions during coalescing.
*
* Segregated lists: partition the block sizes by powers of two
* starting from 3 blocks, because it's the minimum size requirement
*
*/
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "mm.h"
#include "memlib.h"
/* If you want debugging output, use the following macro. When you hand
* in, remove the #define DEBUG line. */
#ifdef DEBUG
# define dbg_printf(...) printf(__VA_ARGS__)
# define dbg_printblock(a) printblock(a)
#else
# define dbg_printf(...)
# define dbg_printblock(a)
#endif
/* do not change the following! */
#ifdef DRIVER
/* create aliases for driver tests */
#define malloc mm_malloc
#define free mm_free
#define realloc mm_realloc
#define calloc mm_calloc
#endif /* def DRIVER */
/* Basic constants and macros */
#define WSIZE 4 /* word size (bytes) */
#define DSIZE 8 /* doubleword size (bytes) */
#define CHUNKSIZE (1<<12) /* initial heap size (bytes) */
#define OVERHEAD 16 /* overhead of header and footer (bytes) */
#define MAX(x, y) ((x) > (y)? (x) : (y))
/* Pack a size and allocated bit into a word */
#define PACK(size, alloc) ((size) | (alloc))
/* Read and write a word at address p */
#define GET(p) (*(unsigned int *)(p))
#define PUT(p, val) (*(unsigned int *)(p) = (val))
#define PUT_ADDR(p, val) (*(int *)(p) = (int)(long)(val))
/* Read the size and allocated fields from address p */
#define GET_SIZE(p) (GET(p) & ~0x7)
#define GET_ALLOC(p) (GET(p) & 0x1)
/* Given block ptr bp, compute address of its header and footer */
#define HDRP(bp) ((char *)(bp) - WSIZE)
#define FTRP(bp) ((char *)(bp) + GET_SIZE(HDRP(bp)) - DSIZE)
/* Given block ptr bp, read address of its next/prev free block pointer */
#define NEXTP(bp) ((int *)((char *)(bp)))
#define PREVP(bp) ((int *)((char *)(bp) + WSIZE))
/* Given block ptr bp, compute address of next and previous blocks */
#define NEXT_BLKP(bp) ((char *)(bp) + GET_SIZE(((char *)(bp) - WSIZE)))
#define PREV_BLKP(bp) ((char *)(bp) - GET_SIZE(((char *)(bp) - DSIZE)))
/* single word (4) or double word (8) alignment */
#define ALIGNMENT 8
/* rounds up to the nearest multiple of ALIGNMENT */
#define ALIGN(p) (((size_t)(p) + (ALIGNMENT-1)) & ~0x7)
#define SIZE_T_SIZE (ALIGN(sizeof(size_t)))
#define MIN_BLKSIZE 16
/* class no: 0 - NUM_FREELIST-1 */
#define NUM_FREELIST 10
/* The only global variable is a pointer to the first block */
char *heap_listp;
/* function prototypes for internal helper routines */
inline void *extend_heap(size_t words);
inline void place(void *bp, size_t asize);
inline void *find_fit(size_t asize);
inline void *coalesce(void *bp);
inline void printblock(void *bp);
inline void checkblock(void *bp);
inline void delete_freenode(void *bp);
inline void insert_freenode(void *bp);
inline void printfreelist();
inline void *getroot(int class);
inline int getclass(size_t size);
inline void check_heapboundaries(void *heapstart, void *heapend);
inline void checkfreelist(int freeblockcount);
inline int aligned(const void *p);
inline int in_heap(const void *p);
inline void *offset2addr(int offset);
inline void *next_free_blck(void *bp);
inline void *prev_free_blck(void *bp);
/*
* mm_init - Initialize the memory manager
* segregated list - save each root at beginning, each root is 2*DSIZE
*/
int mm_init(void)
{
/* create the initial empty heap */
if ((heap_listp = mem_sbrk(DSIZE+NUM_FREELIST*DSIZE*2)) == NULL)
return -1;
PUT(heap_listp, 0); /* alignment padding */
PUT(heap_listp+2*NUM_FREELIST*DSIZE+WSIZE, PACK(0, 1)); /* epilogue header */
heap_listp += DSIZE;
for (int i = 0; i < NUM_FREELIST; i++) {
char *root = getroot(i);
PUT(root-WSIZE, PACK(OVERHEAD, 1)); /* prologue header */
PUT_ADDR(root, NULL); /* root next free node */
PUT(root+DSIZE, PACK(OVERHEAD, 1)); /* prologue footer */
}
/* Extend the empty heap with a free block of CHUNKSIZE bytes */
if (extend_heap(CHUNKSIZE/WSIZE) == NULL)
return -1;
return 0;
}
/*
* mm_malloc - Allocate a block with at least size bytes of payload
*/
void *malloc(size_t size)
{
dbg_printf("Calling mm_malloc........");
size_t asize; /* adjusted block size */
size_t extendsize; /* amount to extend heap if no fit */
char *bp;
/* Ignore spurious requests */
if (size <= 0)
return NULL;
/* Adjust block size to include overhead and alignment reqs. */
asize = MAX(ALIGN(size + SIZE_T_SIZE), MIN_BLKSIZE);
/* Search the free list for a fit */
if ((bp = find_fit(asize)) != NULL) {
place(bp, asize);
return bp;
}
/* No fit found. Get more memory and place the block */
extendsize = MAX(asize,CHUNKSIZE/8);
if ((bp = extend_heap(extendsize/WSIZE)) == NULL)
return NULL;
place(bp, asize);
return bp;
}
/*
* mm_free - Free a block
*/
void free(void *bp)
{
dbg_printf("Calling mm_free........");
if(!bp) return;
size_t size = GET_SIZE(HDRP(bp));
PUT(HDRP(bp), PACK(size, 0));
PUT(FTRP(bp), PACK(size, 0));
coalesce(bp);
}
/*
* delete_freenode - delete the block from free list when it is allocated
*/
inline void delete_freenode(void *bp)
{
void *next_free_block_addr = next_free_blck(bp);
void *prev_free_block_addr = (void *)prev_free_blck(bp);
PUT_ADDR(NEXTP(prev_free_block_addr), next_free_block_addr);
if (next_free_block_addr != NULL) {
PUT_ADDR(PREVP(next_free_block_addr), prev_free_block_addr);
}
}
/*
* insert_freenode - insert the freed block to the free list
*/
inline void insert_freenode(void *bp)
{
size_t size = GET_SIZE(HDRP(bp));
void *root = getroot(getclass(size));
void *nextp = next_free_blck(root);
void *prevp = root;
for (; nextp!=NULL && GET_SIZE(HDRP(nextp)) < size; prevp = nextp, nextp = (char *)next_free_blck(nextp)) {
}
PUT_ADDR(NEXTP(bp), nextp);
PUT_ADDR(PREVP(bp), prevp);
PUT_ADDR(NEXTP(prevp), bp);
if (nextp != NULL) {
PUT_ADDR(PREVP(nextp), bp);
}
}
/*
* realloc - you may want to look at mm-naive.c
*/
void *realloc(void *oldptr, size_t size)
{
dbg_printf("Calling mm_relloc........");
size_t oldsize;
void *newptr;
/* If size == 0 then this is just free, and we return NULL. */
if(size == 0) {
free(oldptr);
return 0;
}
/* If oldptr is NULL, then this is just malloc. */
if(oldptr == NULL) {
return malloc(size);
}
oldsize = GET_SIZE(HDRP(oldptr));
/* If size <= old size or the old block has a free block next to it,
then just return the oldptr
*/
size_t asize = MAX(ALIGN(size + SIZE_T_SIZE), MIN_BLKSIZE);
// smaller than the old block
if (asize <= oldsize) {
place(oldptr, asize);
return oldptr;
}
else {
// enough space in next free block
if (!GET_ALLOC(HDRP(NEXT_BLKP(oldptr)))) {
size_t nsize = GET_SIZE(HDRP(NEXT_BLKP(oldptr))) + oldsize;
if (nsize > asize) {
delete_freenode(NEXT_BLKP(oldptr));
PUT(HDRP(oldptr), PACK(nsize, 1));
PUT(FTRP(oldptr), PACK(nsize,1));
place(oldptr, asize);
return oldptr;
}
}
}
newptr = malloc(size);
/* If realloc() fails the original block is left untouched */
if(!newptr) {
return 0;
}
/* Copy the old data. */
if(size < oldsize) oldsize = size;
memcpy(newptr, oldptr, oldsize);
/* Free the old block. */
free(oldptr);
return newptr;
}
/*
* calloc - you may want to look at mm-naive.c
* This function is not tested by mdriver, but it is
* needed to run the traces.
*/
void *calloc (size_t nmemb, size_t size) {
size_t bytes = nmemb * size;
void *newptr;
newptr = malloc(bytes);
memset(newptr, 0, bytes);
return newptr;
}
/*
* mm_checkheap - Check the heap for consistency
*/
void mm_checkheap(int verbose)
{
if (verbose)
printf("Check heap: \n");
char *bp = heap_listp;
int free_block_flag = 0;
int free_block_count = 0;
if (verbose)
printf("Heap (%p):\n", heap_listp);
// check prologue block
if ((GET_SIZE(HDRP(heap_listp)) != OVERHEAD) || !GET_ALLOC(HDRP(heap_listp)))
printf("Bad prologue header\n");
checkblock(heap_listp);
for (bp = heap_listp; GET_SIZE(HDRP(bp)) > 0; bp = NEXT_BLKP(bp)) {
if (verbose)
printblock(bp);
checkblock(bp);
// check coalescing
if (!GET_ALLOC(HDRP(bp))) {
if (free_block_flag == 1) {
printf("Error: consecutive free blocks %p | %p in the heap.\n", PREV_BLKP(bp),bp);
}
free_block_flag = 1;
free_block_count++;
} else {
free_block_flag = 0;
}
}
if (verbose)
printblock(bp);
// check epilogue block
if ((GET_SIZE(HDRP(bp)) != 0) || !(GET_ALLOC(HDRP(bp))))
printf("Bad epilogue header\n");
// print heap boundaries
check_heapboundaries(heap_listp-DSIZE, bp-1);
if (verbose) {
printfreelist();
}
checkfreelist(free_block_count);
}
/* The remaining routines are internal helper routines */
/*
* getclass - Get class for given size
*/
inline int getclass(size_t size)
{
int block = size / DSIZE;
if (block <= 4) {
return 0;
}
if (block <= 8) {
return 1;
}
if (block <= 16) {
return 2;
}
if (block <= 32) {
return 3;
}
if (block <= 64) {
return 4;
}
if (block <= 128) {
return 5;
}
if (block <= 256) {
return 6;
}
if (block <= 512) {
return 7;
}
if (block <= 1024) {
return 8;
}
return 9;
}
/*
* getroot - Get root node for corresponding class
*/
inline void *getroot(int class)
{
return heap_listp + class * 2 * DSIZE;
}
/*
* extend_heap - Extend heap with free block and return its block pointer
*/
inline void *extend_heap(size_t words)
{
void *bp;
size_t size;
/* Allocate an even number of words to maintain alignment */
size = (words % 2) ? (words+1) * WSIZE : words * WSIZE;
if ((bp = mem_sbrk(size)) == (void *) -1)
return NULL;
/* Initialize free block header/footer and the epilogue header */
PUT(HDRP(bp), PACK(size, 0)); /* free block header */
PUT(FTRP(bp), PACK(size, 0)); /* free block footer */
PUT(HDRP(NEXT_BLKP(bp)), PACK(0, 1)); /* new epilogue header */
/* Coalesce if the previous block was free */
return coalesce(bp);
}
/*
* place - Place block of asize bytes at start of free block bp
* and split if remainder would be at least minimum block size
*/
inline void place(void *bp, size_t asize)
{
size_t csize = GET_SIZE(HDRP(bp));
int is_realloc = GET_ALLOC(HDRP(bp));
if ((csize - asize) >= MIN_BLKSIZE) {
if (!is_realloc) {
delete_freenode(bp);
}
PUT(HDRP(bp), PACK(asize, 1));
PUT(FTRP(bp), PACK(asize, 1));
dbg_printblock(bp);
bp = NEXT_BLKP(bp);
PUT(HDRP(bp), PACK(csize-asize, 0));
PUT(FTRP(bp), PACK(csize-asize, 0));
dbg_printblock(bp);
insert_freenode(bp);
dbg_printblock(bp);
}
else {
if (!is_realloc) {
delete_freenode(bp);
}
PUT(HDRP(bp), PACK(csize, 1));
PUT(FTRP(bp), PACK(csize, 1));
}
}
/*
* find_fit - Find a fit for a block with asize bytes
*/
inline void *find_fit(size_t asize)
{
dbg_printf("FINDING FIT: ");
void *bp;
int class = getclass(asize);
for (int i = class; i < NUM_FREELIST; i++) {
void *root = getroot(i);
/* first fit search */
for (bp = next_free_blck(root); bp != NULL; bp = next_free_blck(bp)) {
dbg_printf(" %lx > ", (long)bp);
if (asize <= GET_SIZE(HDRP(bp))) {
dbg_printf("FOUND!\n");
return bp;
}
}
}
dbg_printf("NOT FOUND :(\n");
return NULL; /* no fit */
}
/*
* coalesce - boundary tag coalescing. Return ptr to coalesced block
*/
inline void *coalesce(void *bp)
{
size_t prev_alloc = GET_ALLOC(FTRP(PREV_BLKP(bp)));
size_t next_alloc = GET_ALLOC(HDRP(NEXT_BLKP(bp)));
size_t size = GET_SIZE(HDRP(bp));
dbg_printblock(bp);
if (prev_alloc && next_alloc) { /* Case 1 */
insert_freenode(bp); /* insert the free node to the head of freelist */
return bp;
}
else if (prev_alloc && !next_alloc) { /* Case 2 */
size += GET_SIZE(HDRP(NEXT_BLKP(bp)));
delete_freenode(NEXT_BLKP(bp));
PUT(HDRP(bp), PACK(size, 0));
PUT(FTRP(bp), PACK(size,0));
insert_freenode(bp);
return(bp);
}
else if (!prev_alloc && next_alloc) { /* Case 3 */
size += GET_SIZE(HDRP(PREV_BLKP(bp)));
delete_freenode(PREV_BLKP(bp));
PUT(FTRP(bp), PACK(size, 0));
PUT(HDRP(PREV_BLKP(bp)), PACK(size, 0));
insert_freenode(PREV_BLKP(bp));
return(PREV_BLKP(bp));
}
else { /* Case 4 */
size += GET_SIZE(HDRP(PREV_BLKP(bp))) +
GET_SIZE(FTRP(NEXT_BLKP(bp)));
delete_freenode(PREV_BLKP(bp));
delete_freenode(NEXT_BLKP(bp));
PUT(HDRP(PREV_BLKP(bp)), PACK(size, 0));
PUT(FTRP(NEXT_BLKP(bp)), PACK(size, 0));
insert_freenode(PREV_BLKP(bp));
return(PREV_BLKP(bp));
}
}
/*
* printblock - print the header, footer and pointers of each block
*/
inline void printblock(void *bp)
{
size_t hsize, halloc, fsize, falloc;
long next, prev;
hsize = GET_SIZE(HDRP(bp));
halloc = GET_ALLOC(HDRP(bp));
fsize = GET_SIZE(FTRP(bp));
falloc = GET_ALLOC(FTRP(bp));
if (hsize == 0) {
printf("%p: EOL\n", bp);
return;
}
if (!halloc || (char *)bp < (heap_listp+2*NUM_FREELIST*DSIZE)) {
next = (long)next_free_blck(bp);
prev = (long)prev_free_blck(bp);
printf("%p: header: [%d:%c] next: %lx prev: %lx footer: [%d:%c]\n", bp,
(int)hsize, (halloc ? 'a' : 'f'), next, prev,
(int)fsize, (falloc ? 'a' : 'f'));
} else {
printf("%p: header: [%d:%c] footer: [%d:%c]\n", bp,
(int)hsize, (halloc ? 'a' : 'f'),
(int)fsize, (falloc ? 'a' : 'f'));
}
}
/*
* printfreelist - print each free list
*/
inline void printfreelist()
{
for (int i = 0; i < NUM_FREELIST; i++) {
printf("Free list %d: ", i);
char *bp = getroot(i);
for (; bp != NULL; bp = next_free_blck(bp)) {
printf(" %lx -> ",(long)bp);
}
printf("END\n");
}
}
/*
* checkblock - check alignment, minmium size requirement,
and consistency of header and footer
*/
inline void checkblock(void *bp)
{
if (!aligned(bp))
printf("Error: %p is not aligned\n", bp);
if (((char *)bp >= (heap_listp+2*NUM_FREELIST*DSIZE)) && GET_SIZE(HDRP(bp)) < MIN_BLKSIZE) {
printf("Error: %p is less than the minimum size requirement\n", bp);
}
if (GET(HDRP(bp)) != GET(FTRP(bp)))
printf("Error: header does not match footer\n");
}
/*
* check_heapboundaries - check if heap boundaries matches head and end blocks
*/
inline void check_heapboundaries(void *heapstart, void *heapend)
{
if (heapstart != mem_heap_lo()) {
printf("Error: heap start point %p is not equaled to heap low boundary %p\n",
heapstart, mem_heap_lo());
}
if (heapend != mem_heap_hi()) {
printf("Error: heap end point %p is not equaled to heap high boundary %p\n",
heapend, mem_heap_hi());
}
}
/*
* checkfreelist - check the free list
*/
inline void checkfreelist(int freeblockcount)
{
int free_count = 0;
for (int i = 0; i < NUM_FREELIST; i++) {
char *bp = getroot(i);
bp = next_free_blck(bp);
for (; bp != NULL; bp = next_free_blck(bp),free_count++) {
void *next_free_block_addr = (void *)next_free_blck(bp);
void *prev_free_block_addr = (void *)prev_free_blck(bp);
// check pointer consistency
if ((next_free_block_addr != NULL) && ((long)prev_free_blck(next_free_block_addr) != (long)bp)) {
printf("Error: pointers not consistent:\n");
printblock(bp);
printblock(next_free_block_addr);
}
// check pointers in heap boundaries
if (!in_heap(next_free_block_addr) || !in_heap(prev_free_block_addr)) {
printf("Error: pointers not in heap %p or %p\n",next_free_block_addr,prev_free_block_addr);
}
// check if block falls in the right size class
if (getclass(GET_SIZE(HDRP(bp))) != i) {
printf("Error: block not fall within bucket size range\n");
}
}
}
// check if free counts match
if (free_count != freeblockcount) {
printf("Error: free count not matched: %d vs %d\n",freeblockcount,free_count);
}
}
/*
* Return whether the pointer is in the heap.
* May be useful for debugging.
*/
inline int in_heap(const void *p) {
if (p == NULL) {
return 1;
}
return p <= mem_heap_hi() && p >= mem_heap_lo();
}
/*
* Return whether the pointer is aligned.
* May be useful for debugging.
*/
inline int aligned(const void *p) {
return (size_t)ALIGN(p) == (size_t)p;
}
/*
* offset2addr - restore the offset to address
*/
inline void *offset2addr(int offset)
{
if (offset) {
return (void *)((long)offset | 0x800000000);
}
else {
return NULL;
}
}
/*
* next_free_blck - Given block bp, get next free block
*/
inline void *next_free_blck(void *bp)
{
int offset = *NEXTP(bp);
return offset2addr(offset);
}
/*
* prev_free_blck - Given block bp, get previous block
*/
inline void *prev_free_blck(void *bp)
{
int offset = *PREVP(bp);
return offset2addr(offset);
}