官网的实习手册是缺了测试材料的，所以我建议你直接从这里下载吧： https://github.com/happysnaker/CSAPPLabs/tree/CSAPP/molloc-Lab
实验仅要求我们修改mm.c文件，要求完成init, molloc, free, recalloc 四个函数，其中部分与系统接口的函数已在memlib.c文件中给出。
完成之后，我们需要键入以下三条命令来跑分：
make clean
make mdriver
./mdriver
这个实验难度特别大，其中非常容易碰到段错误，以至于我最后一个分离式的链表仍然没有实现，实乃一个遗憾。立个flag，2021年一定要实现它！
首次适配从头遍历链表，找到空闲块。这个跑分不是很理想，甚至还不及格，只有56分。这个就是书上的思路，其中要自己完善两个函数。 代码：隐式空闲链表加首次适配实现
下一次适配从上次操作的时候开始遍历。这种方式竟然出奇的理想，跑了82分:
/*
Team Name:happysnaker
Member 1 :qwewqewqqe:qwewqewqqe
Using default tracefiles in traces/
Perf index = 42 (util) + 40 (thru) = 82/100
*/
我们留下一个bookstr来表示上一次操作时的指针，由于我们每一次释放空闲块都让这个指针指向了空闲块，所以下一次分配时速度非常块，可以看到效率部分拿了满分(40)，但利用率却不理想。
代码：
/*
Team Name:happysnaker
Member 1 :qwewqewqqe:qwewqewqqe
Using default tracefiles in traces/
Perf index = 42 (util) + 40 (thru) = 82/100
*/
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <unistd.h>
#include <string.h>
#include "mm.h"
#include "memlib.h"
team_t team = {
/* Team name */
"ateam",
/* First member's full name */
"Harry Bovik",
/* First member's email address */
"[email protected]",
/* Second member's full name (leave blank if none) */
"",
/* Second member's email address (leave blank if none) */
""
};
/* single word (4) or double word (8) alignment */
#define ALIGNMENT 8
/* rounds up to the nearest multiple of ALIGNMENT */
#define ALIGN(size) (((size) + (ALIGNMENT-1)) & ~0x7)
#define SIZE_T_SIZE (ALIGN(sizeof(size_t)))
#define WSIZE 4
#define DSIZE 8
#define CHUNKSIZE (1 << 12)
#define MAX(X, Y) ((X) > (Y) ? (X) : (Y))
#define PACK(size, alloc) ((size) | (alloc)) /*设置头部或脚部*/
#define GET(p) (*(unsigned int*)(p))
#define PUT(p, val) (*(unsigned int*)(p) = (val))
#define GET_SIZE(P) (GET(P) & ~0X7)
#define GET_ALLOC(P) (GET(P) & 0X1)
#define HDRP(bp) ((char*)(bp) - WSIZE) /*获取头部指针*/
#define FTRP(bp) ((char*)(bp) + GET_SIZE(HDRP(bp)) - DSIZE) /*根据头部获取脚部指针*/
#define NEXT_BLKP(bp) ((char*)(bp) + GET_SIZE(((char*)(bp) - WSIZE))) /*下一个指向有效载荷的指针*/
#define PREV_BLKP(bp) ((char*)(bp) - GET_SIZE(((char*)(bp) - DSIZE)))
static void* extend_heap(size_t words);
static void* coalesce(void* bp);
static void *find_fit(size_t size);
static void place(void *bp,size_t asize);
static char *heap_listp = 0;
static void* bookptr;
/*
* mm_init - initialize the malloc package.
*/
int mm_init(void)
{
if ((heap_listp = mem_sbrk(4 * WSIZE)) == (void*)-1)
return -1;
PUT(heap_listp + (1 * WSIZE), PACK(DSIZE, 1));
PUT(heap_listp + (2 * WSIZE), PACK(DSIZE, 1));
PUT(heap_listp + (3 * WSIZE), PACK(0, 1));
heap_listp += (2 * WSIZE);
bookptr = (unsigned int)heap_listp + DSIZE; /*初始化*/
if (extend_heap(CHUNKSIZE/WSIZE) == NULL)
return -1;
return 0;
}
static void* extend_heap(size_t words){
char* bp;
size_t size;
size = (words % 2) ? (words + 1) * WSIZE : words * WSIZE;
if ((long)(bp = mem_sbrk(size)) == -1)
return NULL;
PUT(HDRP(bp), PACK(size, 0));
PUT(FTRP(bp), PACK(size, 0));
PUT(HDRP(NEXT_BLKP(bp)), PACK(0, 1));
bookptr = coalesce(bp); /*让它指向空闲指针*/
return bookptr;
}
static 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));
if (prev_alloc && next_alloc)
return bp;
else if (prev_alloc && !next_alloc){
size += GET_SIZE(HDRP(NEXT_BLKP(bp)));
PUT(FTRP(NEXT_BLKP(bp)), PACK(size, 0));
PUT(HDRP(bp), PACK(size, 0));
}
else if (!prev_alloc && next_alloc){
size += GET_SIZE(HDRP(PREV_BLKP(bp)));
PUT(FTRP(bp), PACK(size, 0));
PUT(HDRP(PREV_BLKP(bp)), PACK(size, 0));
bp = PREV_BLKP(bp);
}
else{
size += GET_SIZE(HDRP(PREV_BLKP(bp))) + GET_SIZE(HDRP(NEXT_BLKP(bp)));
PUT(HDRP(PREV_BLKP(bp)), PACK(size, 0));
PUT(FTRP(NEXT_BLKP(bp)), PACK(size, 0));
bp = PREV_BLKP(bp);
}
return bp;
}
/*
* mm_malloc - Allocate a block by incrementing the brk pointer.
* Always allocate a block whose size is a multiple of the alignment.
*/
void *mm_malloc(size_t size)
{
char *bp;
size_t asize;
size_t extendsize;
if (size <= 0)
return NULL;
if (size <= DSIZE)
asize = 2 * DSIZE;
else
asize = DSIZE * ((size + DSIZE + (DSIZE - 1)) / DSIZE);
if ((bp = find_fit(asize)) != NULL){
place(bp, asize);
bookptr = bp;
return bp;
}
extendsize = MAX(asize, CHUNKSIZE);
if ((bp = extend_heap(extendsize / WSIZE)) == NULL)
return NULL;
place(bp, asize);
bookptr = bp; /*指向上一个分配的块*/
return bp;
}
/*
* mm_free - Freeing a block does nothing.
*/
void mm_free(void *ptr)
{
size_t size = GET_SIZE(HDRP(ptr));
PUT(HDRP(ptr), PACK(size, 0));
PUT(FTRP(ptr), PACK(size, 0));
bookptr = coalesce(ptr); /*指向空闲块*/
return;
}
/*
* mm_realloc - Implemented simply in terms of mm_malloc and mm_free
*/
static void *find_fit(size_t size){
while (GET_SIZE(HDRP(bookptr)) > 0){
if (GET_SIZE(HDRP(bookptr)) >= size && GET_ALLOC(HDRP(bookptr)) == 0)
return bookptr;
bookptr = NEXT_BLKP(bookptr); /*别忘了更新它*/
}
return NULL;
}
static void place(void *bp,size_t asize){
size_t nowsize = GET_SIZE(HDRP(bp));
if (nowsize - asize < 2 * DSIZE){
PUT(HDRP(bp), PACK(nowsize, 1));
PUT(FTRP(bp), PACK(nowsize, 1));
}
else{
PUT(HDRP(bp), PACK(asize, 1));
PUT(FTRP(bp), PACK(asize, 1));
PUT(HDRP(NEXT_BLKP(bp)), PACK(nowsize - asize, 0));
PUT(FTRP(NEXT_BLKP(bp)), PACK(nowsize - asize, 0));
}
return;
}
/*
* mm_realloc - Implemented simply in terms of mm_malloc and mm_free
*/
void *mm_realloc(void *ptr, size_t size)
{
size_t oldsize = GET_SIZE(HDRP(ptr));
void* newptr = mm_malloc(size);
if (!newptr)
return 0;
bookptr = newptr; /*指向空闲块*/
if (!ptr)
return newptr;
memcpy(newptr, ptr, (size < oldsize ? size : oldsize));
mm_free(ptr);
return newptr;
}
找到最小适合的块，提高利用率，这个跑分不是很理想，只有56分。代码： 隐式空闲链表加最佳适配
这一次采用双向链表，块的大小至少需要16字节，当前块指针bp指向的四字节保存着上一空闲块的指针，bp + 4保存着下一空闲块的指针。当我们有空闲块时，我们简单的插入到根节点处。
/*
Team Name:happysnaker
Member 1 :qwewqewqqe:qwewqewqqe
Using default tracefiles in traces/
Perf index = 45 (util) + 40 (thru) = 85/100
*/
代码：
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <unistd.h>
#include <string.h>
#include "mm.h"
#include "memlib.h"
/*********************************************************
* NOTE TO STUDENTS: Before you do anything else, please
* provide your team information in the following struct.
********************************************************/
team_t team =
{
/* Team name */
"Xwqe",
/* First member's full name */
"qewqe",
/* First member's email address */
"sadsa",
/* Second member's full name (leave blank if none) */
"",
/* Second member's email address (leave blank if none) */
""
};
/* single word (4) or double word (8) alignment */
#define ALIGNMENT 8
/* rounds up to the nearest multiple of ALIGNMENT */
#define ALIGN(size) (((size) + (ALIGNMENT-1)) & ~0x7)
#define SIZE_T_SIZE (ALIGN(sizeof(size_t)))
#define WSIZE 4
#define DSIZE 8 /*Double word size*/
#define CHUNKSIZE (1<<12) /*the page size in bytes is 4K*/
#define MAX(x,y) ((x)>(y)?(x):(y))
#define PACK(size,alloc) ((size) | (alloc))
#define GET(p) (*(unsigned int *)(p))
#define PUT(p,val) (*(unsigned int *)(p) = (val))
#define GET_SIZE(p) (GET(p) & ~0x7)
#define GET_ALLOC(p) (GET(p) & 0x1)
#define HDRP(bp) ((char *)(bp)-WSIZE)
#define FTRP(bp) ((char *)(bp)+GET_SIZE(HDRP(bp))-DSIZE)
#define PREV_BLKP(bp) ((char *)(bp)-GET_SIZE(((char *)(bp)-DSIZE)))
#define NEXT_BLKP(bp) ((char *)(bp)+GET_SIZE(((char *)(bp)-WSIZE)))
#define NEXT_RP(bp) ((unsigned int)(bp)+WSIZE) /*指向下一空闲块指针*/
int mm_check(char *function);
static void *extend_heap(size_t dwords);
static void *coalesce(void *bp);
static void *find_fit(size_t size);
static void place(void *bp,size_t asize);
void __insert(char *p);
void __remove(char *p);
static char *heap_listp = NULL;
static char *root = NULL; /*这是我们的根节点*/
/*
* mm_init - initialize the malloc package.
* The return value should be -1 if there was a problem in performing the initialization, 0 otherwise
*/
int mm_init(void){
if((heap_listp = mem_sbrk(6*WSIZE))==(void *)-1) return -1;
PUT(heap_listp,0);
PUT(heap_listp+(1*WSIZE),0);
PUT(heap_listp+(2*WSIZE),0); /*内存对齐*/
PUT(heap_listp+(3*WSIZE),PACK(DSIZE,1));
PUT(heap_listp+(4*WSIZE),PACK(DSIZE,1)); /*内存对齐*/
PUT(heap_listp+(5*WSIZE),PACK(0,1)); /*尾巴*/
root = heap_listp + (1*WSIZE);/*初始化根节点*/
heap_listp += (4*WSIZE);
if((extend_heap(CHUNKSIZE/DSIZE)) == NULL)
return -1;
return 0;
}
/*
* mm_malloc - Allocate a block by incrementing the brk pointer.
* Always allocate a block whose size is a multiple of the alignment.
*/
void *mm_malloc(size_t size){
size_t asize;
size_t extendsize;
char *bp;
if(size ==0)
return NULL;
if(size <= DSIZE)
asize = 2*(DSIZE);
else
asize = (DSIZE) * ((size + DSIZE + (DSIZE-1)) / (DSIZE));
if((bp = find_fit(asize))!= NULL){
place(bp,asize);
return bp;
}
extendsize = MAX(asize,CHUNKSIZE);
if((bp = extend_heap(extendsize/DSIZE))==NULL)
return NULL;
place(bp,asize);
return bp;
}
/*
* mm_free - Freeing a block does nothing.
*/
void mm_free(void *bp){
if(bp == NULL)
return;
size_t size = GET_SIZE(HDRP(bp));
PUT(HDRP(bp), PACK(size, 0));
PUT(FTRP(bp), PACK(size, 0));
PUT(NEXT_RP(bp),0); /*刚释放的块，设置前后指针为null*/
PUT(bp,0);
coalesce(bp);
}
/*
* mm_realloc - Implemented simply in terms of mm_malloc and mm_free
*/
void *mm_realloc(void *ptr, size_t size){
void *newptr = mm_malloc(size);
if(!newptr){
return 0;
}
if(ptr == NULL){
return newptr;
}
size_t oldsize = GET_SIZE(HDRP(ptr));
memcpy(newptr, ptr, oldsize < size ? oldsize : size);
mm_free(ptr);
return newptr;
}
static void *find_fit(size_t size){
/*first fit*/
char *bp = GET(root);
while(bp != NULL){
if(GET_SIZE(HDRP(bp)) >= size)
return bp;
bp = GET(NEXT_RP(bp));
}
return NULL;
}
static void place(void *bp,size_t asize)
{
size_t csize = GET_SIZE(HDRP(bp));
__remove(bp); /*使用了这个块，切记移除它*/
if(csize-asize >= 2 *DSIZE){
PUT(HDRP(bp),PACK(asize,1));
PUT(FTRP(bp),PACK(asize,1));
PUT(HDRP(NEXT_BLKP(bp)),PACK(csize-asize,0));
PUT(FTRP(NEXT_BLKP(bp)),PACK(csize-asize,0));
PUT(NEXT_RP(bp),0);
PUT((NEXT_BLKP(bp)),0);
coalesce(NEXT_BLKP(bp));
}
else{
PUT(HDRP(bp),PACK(csize,1));
PUT(FTRP(bp),PACK(csize,1));
}
}
static void *extend_heap(size_t words)
{
char *bp;
size_t size;
size = (words % 2) ? (words+1) * DSIZE : words * DSIZE;
if((long)(bp = mem_sbrk(size))==(void *)-1)
return NULL;
PUT(HDRP(bp),PACK(size,0));
PUT(FTRP(bp),PACK(size,0));
PUT(HDRP(NEXT_BLKP(bp)),PACK(0,1));
PUT(NEXT_RP(bp),0);
PUT(bp,0);
return coalesce(bp);
}
/*coalesce the empty block*/
static 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));
/*coalesce the block and change the point*/
if(prev_alloc && !next_alloc){
size += GET_SIZE(HDRP(NEXT_BLKP(bp)));
__remove(NEXT_BLKP(bp)); /*使用了这个块，切记移除它*/
PUT(HDRP(bp), PACK(size,0));
PUT(FTRP(bp), PACK(size,0));
}
else if(!prev_alloc && next_alloc){
size += GET_SIZE(HDRP(PREV_BLKP(bp)));
__remove(PREV_BLKP(bp));/*使用了这个块，切记移除它*/
PUT(FTRP(bp),PACK(size,0));
PUT(HDRP(PREV_BLKP(bp)),PACK(size,0));
bp = PREV_BLKP(bp);
}
else if (!prev_alloc && !next_alloc){
size +=GET_SIZE(FTRP(NEXT_BLKP(bp)))+ GET_SIZE(HDRP(PREV_BLKP(bp)));
__remove(PREV_BLKP(bp));/*使用了这个块，切记移除它*/
__remove(NEXT_BLKP(bp));/*使用了这个块，切记移除它*/
PUT(FTRP(NEXT_BLKP(bp)),PACK(size,0));
PUT(HDRP(PREV_BLKP(bp)),PACK(size,0));
bp = PREV_BLKP(bp);
}
__insert(bp);/*新的空闲块，记住插入*/
return bp;
}
inline void __insert(char *bp)
{
//PUT(bp, root); 这个操作有段错误，挺离谱的
char *next = GET(root);
if(next != NULL)
PUT(next, bp);
PUT(NEXT_RP(bp), next);
PUT(root,bp);
}
inline void __remove(char *bp){
char *pre = GET((bp));
char *next = GET(NEXT_RP(bp));
/*因为上面插入操作不能置bp的前驱为root,所以这个是必须考虑的，这个代表前面就是根节点了 */
if(pre == NULL){
if(next != NULL)
PUT(next,0);
PUT(root,next);
}
else{
if(next != NULL)
PUT((next),pre);
PUT(NEXT_RP(pre),next);
}
PUT(NEXT_RP(bp),0);
PUT(bp,0);
}
插入操作设置前驱为root竟然有段错误，真是折杀我也，也许是因为不经意间会访问NEXT_RP(root)吧，这个值被我们设置成了NULL。哎，由衷敬佩操作系统开发者，和内存打交道太不容易了。
其实这个在插入时我觉得还可以以升序的方式插入，这样可以提高利用率。可惜了，还是我们的老朋友段错误，哎。
看来想要满绩(90)必须要采用分离适配了，最近被段错误弄的有点晕，不过立个flag，2021年一定要完成它！