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Code Issues Releases Wiki Activity

🆕 回收堆内存给操作系统

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This commit is contained in:
fslongjin
2022-05-11 20:42:53 +08:00
parent edb21695ae
commit 1cc3db5e88
6 changed files with 311 additions and 88 deletions
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108
user/libs/libc/malloc.c
View File

@ -5,6 +5,24 @@
#include <libc/errno.h>
#include <libc/stdio.h>
#define PAGE_4K_SHIFT 12
#define PAGE_2M_SHIFT 21
#define PAGE_1G_SHIFT 30
#define PAGE_GDT_SHIFT 39
// 不同大小的页的容量
#define PAGE_4K_SIZE (1UL << PAGE_4K_SHIFT)
#define PAGE_2M_SIZE (1UL << PAGE_2M_SHIFT)
#define PAGE_1G_SIZE (1UL << PAGE_1G_SHIFT)
// 屏蔽低于x的数值
#define PAGE_4K_MASK (~(PAGE_4K_SIZE - 1))
#define PAGE_2M_MASK (~(PAGE_2M_SIZE - 1))
// 将addr按照x的上边界对齐
#define PAGE_4K_ALIGN(addr) (((unsigned long)(addr) + PAGE_4K_SIZE - 1) & PAGE_4K_MASK)
#define PAGE_2M_ALIGN(addr) (((unsigned long)(addr) + PAGE_2M_SIZE - 1) & PAGE_2M_MASK)
/**
* @brief 显式链表的结点
*
@ -23,14 +41,9 @@ static uint64_t brk_managed_addr = 0; // 堆区域已经被管理的地址
// 空闲链表
// 按start_addr升序排序
static malloc_mem_chunk_t *malloc_free_list = NULL;
static malloc_mem_chunk_t *malloc_free_list_end = NULL; // 空闲链表的末尾结点
/**
* @brief 获取一块堆内存（不尝试扩大堆内存）
*
* @param size
* @return void* 内存的地址指针，获取失败时返回-ENOMEM
*/
static void *malloc_no_enlarge(ssize_t size);
static uint64_t count_last_free_size = 0; // 统计距离上一次回收内存，已经free了多少内存
/**
* @brief 将块插入空闲链表
@ -39,6 +52,12 @@ static void *malloc_no_enlarge(ssize_t size);
*/
static void malloc_insert_free_list(malloc_mem_chunk_t *ck);
/**
* @brief 当堆顶空闲空间大于2个页的空间的时候，释放1个页
*
*/
static void release_brk();
/**
* @brief 在链表中检索符合要求的空闲块（best fit）
*
@ -52,7 +71,6 @@ static malloc_mem_chunk_t *malloc_query_free_chunk_bf(uint64_t size)
if (malloc_free_list == NULL)
{
printf("free list is none.\n");
return NULL;
}
malloc_mem_chunk_t *ptr = malloc_free_list;
@ -114,15 +132,16 @@ static int malloc_enlarge(int32_t size)
if (brk_base_addr == 0) // 第一次调用，需要初始化
{
brk_base_addr = brk(-1);
printf("brk_base_addr=%#018lx\n", brk_base_addr);
// printf("brk_base_addr=%#018lx\n", brk_base_addr);
brk_managed_addr = brk_base_addr;
brk_max_addr = brk(-2);
}
int64_t tmp = brk_managed_addr + size - brk_max_addr;
if (tmp > 0) // 现有堆空间不足
int64_t free_space = brk_max_addr - brk_managed_addr;
if (free_space < size) // 现有堆空间不足
{
if (sbrk(tmp) != (void *)(-1))
if (sbrk(size - free_space) != (void *)(-1))
brk_max_addr = brk((-2));
else
{
@ -133,10 +152,12 @@ static int malloc_enlarge(int32_t size)
// 扩展管理的堆空间
// 在新分配的内存的底部放置header
// printf("managed addr = %#018lx\n", brk_managed_addr);
malloc_mem_chunk_t *new_ck = (malloc_mem_chunk_t *)brk_managed_addr;
new_ck->length = brk_max_addr - brk_managed_addr;
printf("new_ck->start_addr=%#018lx\tbrk_max_addr=%#018lx\tbrk_managed_addr=%#018lx\n", (uint64_t)new_ck, brk_max_addr, brk_managed_addr);
new_ck->prev = new_ck->next = NULL;
// printf("new_ck->start_addr=%#018lx\tbrk_max_addr=%#018lx\tbrk_managed_addr=%#018lx\n", (uint64_t)new_ck, brk_max_addr, brk_managed_addr);
new_ck->prev = NULL;
new_ck->next = NULL;
brk_managed_addr = brk_max_addr;
malloc_insert_free_list(new_ck);
@ -153,14 +174,19 @@ static void malloc_merge_free_chunk()
if (malloc_free_list == NULL)
return;
malloc_mem_chunk_t *ptr = malloc_free_list->next;
while (ptr)
while (ptr != NULL)
{
// 内存块连续
if (((uint64_t)(ptr->prev) + ptr->prev->length == (uint64_t)ptr))
{
// printf("merged %#018lx and %#018lx\n", (uint64_t)ptr, (uint64_t)(ptr->prev));
// 将ptr与前面的空闲块合并
ptr->prev->length += ptr->length;
ptr->prev->next = ptr->next;
if (ptr->next == NULL)
malloc_free_list_end = ptr->prev;
else
ptr->next->prev = ptr->prev;
// 由于内存组成结构的原因，不需要free掉header
ptr = ptr->prev;
}
@ -178,14 +204,15 @@ static void malloc_insert_free_list(malloc_mem_chunk_t *ck)
if (malloc_free_list == NULL) // 空闲链表为空
{
malloc_free_list = ck;
malloc_free_list_end = ck;
ck->prev = ck->next = NULL;
return;
}
else
{
uint64_t ck_end = (uint64_t)ck + ck->length;
malloc_mem_chunk_t *ptr = malloc_free_list;
while (ptr)
while (ptr != NULL)
{
if ((uint64_t)ptr < (uint64_t)ck)
{
@ -194,13 +221,14 @@ static void malloc_insert_free_list(malloc_mem_chunk_t *ck)
ptr->next = ck;
ck->next = NULL;
ck->prev = ptr;
malloc_free_list_end = ck;
break;
}
else if ((uint64_t)(ptr->next) > (uint64_t)ck)
{
ck->prev = ptr;
ck->next = ptr->next;
ck->prev->next = ck;
ptr->next = ck;
ck->next->prev = ck;
break;
}
@ -254,7 +282,6 @@ void *malloc(ssize_t size)
{
// 尝试合并空闲块
printf("merge\n");
malloc_merge_free_chunk();
ck = malloc_query_free_chunk_bf(size);
@ -262,11 +289,11 @@ void *malloc(ssize_t size)
if (ck)
goto found;
// 找不到合适的块，扩容堆区域
printf("enlarge\n");
if (malloc_enlarge(size) == -ENOMEM)
return (void *)-ENOMEM; // 内存不足
// 扩容后再次尝试获取
printf("query\n");
ck = malloc_query_free_chunk_bf(size);
}
found:;
@ -285,9 +312,11 @@ found:;
if (ck->next != NULL) // 当前不是最后一个块
ck->next->prev = ck->prev;
else
malloc_free_list_end = ck->prev;
// 当前块剩余的空间还能容纳多一个结点的空间，则分裂当前块
if (ck->length - size > sizeof(malloc_mem_chunk_t))
if ((int64_t)(ck->length) - size > sizeof(malloc_mem_chunk_t))
{
malloc_mem_chunk_t *new_ck = (malloc_mem_chunk_t *)(((uint64_t)ck) + size);
new_ck->length = ck->length - size;
@ -297,11 +326,34 @@ found:;
malloc_insert_free_list(new_ck);
}
// printf("ck=%lld\n", (uint64_t)ck);
// 此时链表结点的指针的空间被分配出去
return (void *)((uint64_t)ck + sizeof(uint64_t));
}
/**
* @brief 当堆顶空闲空间大于2个页的空间的时候，释放1个页
*
*/
static void release_brk()
{
// 先检测最顶上的块
// 由于块按照开始地址排列，因此找最后一个块
if (malloc_free_list_end == NULL)
return;
if ((uint64_t)malloc_free_list_end + malloc_free_list_end->length == brk_max_addr && (uint64_t)malloc_free_list_end <= brk_max_addr - (PAGE_2M_SIZE << 1))
{
int64_t delta = (brk_max_addr - (uint64_t)malloc_free_list_end) & PAGE_2M_MASK - PAGE_2M_SIZE;
if (delta <= 0) // 不用释放内存
return;
sbrk(-delta);
brk_max_addr = brk(-2);
brk_managed_addr = brk_max_addr;
malloc_free_list_end->length = brk_max_addr - (uint64_t)malloc_free_list_end;
}
}
/**
* @brief 释放一块堆内存
*
@ -310,7 +362,15 @@ found:;
void free(void *ptr)
{
// 找到结点（此时prev和next都处于未初始化的状态）
malloc_mem_chunk_t * ck = (malloc_mem_chunk_t *)((uint64_t)ptr-sizeof(uint64_t));
malloc_mem_chunk_t *ck = (malloc_mem_chunk_t *)((uint64_t)ptr - sizeof(uint64_t));
// printf("free(): addr = %#018lx\t len=%#018lx\n", (uint64_t)ck, ck->length);
count_last_free_size += ck->length;
malloc_insert_free_list(ck);
if (count_last_free_size > PAGE_2M_SIZE)
{
count_last_free_size = 0;
malloc_merge_free_chunk();
release_brk();
}
}

6
user/libs/libc/unistd.h
View File

@ -63,10 +63,10 @@ pid_t vfork(void);
* @brief 将堆内存调整为end_brk
*
* @param end_brk 新的堆区域的结束地址
* end_brk=0 ===> 返回堆区域的起始地址
* end_brk=-1 ===> 返回堆区域的结束地址
* end_brk=-1 ===> 返回堆区域的起始地址
* end_brk=-2 ===> 返回堆区域的结束地址
* @return uint64_t 错误码
*
*
*/
uint64_t brk(uint64_t end_brk);