？内存管理算法

该文章用作个人纪录。

简要介绍一下两种内存管理算法：

1.小内存管理算法

采用不断分割的方法对内存进行动态分配，分为初始化，分割，释放三个步骤，为了简洁起见，笔者直接放图：
头部初始大内存块尾部
头部内存块内存块内存块内存块尾部

这是整体思想，通过对初始内存块的不断切割，最终形成了各个不同的内存块。

四个函数，第一个init：
头部内存块尾部

复制代码

/*sk
*ai
*ui
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*/

void heap_init()
{

    heap_node *firstnode;
    //这行注释不要删除
    //命名不要随便改，不然有概率导致数组最后八个字节出现segmentation fault问题
    
    uint32_t start_heap ,end_heap;
    //get start address
    start_heap =(uint32_t) allheap;

    /*byte aligment*/
    if( (start_heap & aligment_byte) != 0){
        start_heap += aligment_byte ;
        start_heap &= ~aligment_byte;
        theheap.allsize -=  (size_t)(start_heap - (uint32_t)allheap);//byte aligment means move to high address,so sub it!
    }

    theheap.head.next = (heap_node *)start_heap;
    theheap.head.blocksize = (size_t)0;

    end_heap  = ( start_heap + (uint32_t)config_heap);


    /*byte aligment*/
    if( (end_heap & aligment_byte) != 0){
        end_heap += aligment_byte ;
        end_heap &= ~aligment_byte;
        theheap.allsize =  (size_t)(end_heap - start_heap );

    }
    theheap.tail = (heap_node*)end_heap;
    theheap.tail->blocksize  = 0; 
    theheap.tail->next =NULL;

    firstnode = (heap_node*)start_heap;
    firstnode->next = theheap.tail;

    firstnode->blocksize = theheap.allsize;

}

第二个malloc：
从头开始找_直到找到符合大小的内存块头部内存块内存块内存块内存块尾部
把初始化的内存链表模型作为空闲内存块建立的链表在这条链表上找到符合条件的内存块链表起始结束 prev use new

这条链表上就是空闲内存块链表，内存块被使用就被踢出这条链表，被释放就加入这条链表，如果内存块大于要申请的大小，就把多余的部分切割，然后加入这条内存链表。

复制代码

void *heap_malloc(size_t wantsize)
{
    heap_node *prevnode;
    heap_node *usenode;

    heap_node *newnode;
    size_t aligmentrequisize;

    void *xReturn = NULL;

    if(wantsize <= 0 )
    {
        printf("Error in function: %s at line: %d\n", __func__, __LINE__); \
        exit(-1); 

    }

     
    wantsize += heapstructSize;
    if((wantsize & aligment_byte) != 0x00)
    {
        aligmentrequisize = aligment_byte - (wantsize & aligment_byte);
        wantsize += aligmentrequisize;
    }


    if((wantsize / arm_max_memory) != 0)
    {
        printf("Error in function: %s at line: %d\n", __func__, __LINE__); \
        exit(-1); 

    }
     
    //I will add the TaskSuspend function ,that make there be a atomic operation
    if(theheap.tail== NULL )
    {
        heap_init();
    }

    //

    prevnode = &theheap.head;
    usenode = theheap.head.next;
   

    //the next is valid ?

    while((usenode->blocksize) < wantsize )
    {
        prevnode = usenode;
        usenode = usenode ->next;
    }

    //

    if(usenode == theheap.tail)
    {
        printf("Error in function: %s at line: %d\n", __func__, __LINE__); \
        exit(-1);
    }
    
    xReturn = (void*)(((uint8_t*)usenode) + heapstructSize);

    prevnode->next = usenode->next ;
    /*apart it!*/
    if( (usenode->blocksize - wantsize) > MIN_size )
    {
        newnode = (void*)(((uint8_t*)usenode) + wantsize);

        newnode->blocksize = usenode->blocksize - wantsize;
        usenode->blocksize = wantsize;
        

        newnode->next = prevnode->next ;
        prevnode->next = newnode;
        
    }
   
    
    theheap.allsize-= usenode->blocksize;

    

    if(theheap.allsize < 0U)
    {
        printf("Error in function: %s at line: %d\n", __func__, __LINE__); \
        exit(-1);
    }
    
    usenode->next = NULL;

    // I will write the TaskResume



    

    if(usenode > theheap.tail)
    {

        printf("alheap : %d ,use: %d, tail: %d\n",allheap,usenode,theheap.tail);
        printf("fuck : %s at line: %d\n", __func__, __LINE__); 
        exit(-1);
    }

    
    return xReturn;


}

第三个free：
空闲内存块空闲内存块空闲内存块 Insert

直接插入即可。

复制代码

void heap_free(void *xret)
{
    uint8_t *xFree = (uint8_t*)xret;
    heap_node *xlink;

    if(xFree == NULL)
    {
        printf("Error in function: %s at line: %d\n", __func__, __LINE__); \
        exit(-1);
    }

    xFree -= heapstructSize;
    xlink = (void*)xFree;
    if(xlink->next != NULL)
    {
        printf("Error in function: %s at line: %d\n", __func__, __LINE__); \
        exit(-1);
    }

    // I will tasksuspend
    theheap.allsize += xlink->blocksize;
    InsertFreeBlock((heap_node*)xlink);
     
    // I will TaskResume


}

精髓在于InsertFreeBLOCK:
开始 prev next 结束 Insert ?
start B Insert D E end
后相邻 Insert E start B D end
前相邻 B D start Insert E end
可以只考虑最终结果 B E start Insert D end

如果前后相邻是相互独立的，那么互不影响，如果不独立，通过后，前的顺序可以得到前后都相邻的结果，因此该顺序正确。

复制代码

xInsertBlock->next = first_fitnode->next;
    first_fitnode->next = xInsertBlock;

    getaddr = (uint8_t*)xInsertBlock;
    if((getaddr + xInsertBlock->blocksize) == (uint8_t*)(xInsertBlock->next))
    {
      
        if(xInsertBlock->next != theheap.tail )
        {
            xInsertBlock->blocksize += xInsertBlock->next->blocksize;
            xInsertBlock->next = xInsertBlock->next->next;
        }
        else
        {
            xInsertBlock->next = theheap.tail;
        }
    }
    
    
    
    getaddr = (uint8_t*)first_fitnode;

    if((getaddr + first_fitnode->blocksize) == (uint8_t*) xInsertBlock)
    {
        first_fitnode->blocksize += xInsertBlock->blocksize;
        first_fitnode->next = xInsertBlock->next;
    }