Lwip协议详解（基于Lwip 2.1.0）-内存管理

1、内存管理

1.1 动态内存池
1.1.1 原理
此种方式下，用户只能申请固定大小的空间，例如UDP控制块，TCP控制块。
1.1.2 Lwip的实现源码
下述代码主要用于内存池的初始化，Lwip协议栈中，把所有的pool挨个放在一起，并把它们放在一片连续的内存空间，这样形成了一个巨大的内存池。

void memp_init(void)
{u16_t i;/* for every pool: */for (i = 0; i < LWIP_ARRAYSIZE(memp_pools); i++) {memp_init_pool(memp_pools[i]);#if LWIP_STATS && MEMP_STATSlwip_stats.memp[i] = memp_pools[i]->stats;
#endif}#if MEMP_OVERFLOW_CHECK >= 2/* check everything a first time to see if it worked */memp_overflow_check_all();
#endif /* MEMP_OVERFLOW_CHECK >= 2 */
}

上述代码主要用于对各个内存池的初始memp_pools，那么究竟是怎么初始化的呢?如下述代码所描述的那样，删除了代码中预编译部分。

void memp_init_pool(const struct memp_desc *desc)
{int i;struct memp *memp;*desc->tab = NULL;//初始为空指针memp = (struct memp *)LWIP_MEM_ALIGN(desc->base);//将内存池对齐/* create a linked list of memp elements */for (i = 0; i < desc->num; ++i) {//依次对每种类型的POOL进行操作memp->next = *desc->tab;//将所有pool组成链表*desc->tab = memp;/* cast through void* to get rid of alignment warnings */memp = (struct memp *)(void *)((u8_t *)memp + MEMP_SIZE + desc->size}
}

1.2 动态内存堆栈
1.2.1 原理
动态内存堆分配策略本质上是对一个事先定义好的内存块进行合理有效的组织和管理，其内存分配的策略采用首次拟合方式，只要找到一个比用户空间请求空间大的空闲块，从中切割出合适的块，把剩余的部分返回到动态内存堆中。
在这种策略下，用户申请内存块大小具有最小限制，即请求的大小不能小于MIN_SIZE,否则系统自动请求大小设置为MIN_SIZE。通常用户可以自定义该值达到节省内存空间的目的，不过会导致大的内存块不断被分成小的内存块，内存释放时的过程则相反，内存函数会查看该节点前后的内存块是否空闲，如果空闲则合成一个大的内存空闲块。
采用这种方式其优点时内存浪费小，比较简单，适合小内存。其缺点是如果频繁的动态内存分配和释放，可能会造成严重的内存碎片，如果在内存碎片严重的情况下，可能会导致内存分配不成功

1.2.2 源码分析
（1）初始化

void mem_init(void)
{struct mem *mem;LWIP_ASSERT("Sanity check alignment",(SIZEOF_STRUCT_MEM & (MEM_ALIGNMENT - 1)) == 0);/* align the heap *///内存堆栈对齐，ram 用以记录对齐后的起始地址ram = (u8_t *)LWIP_MEM_ALIGN(LWIP_RAM_HEAP_POINTER);/* initialize the start of the heap */mem = (struct mem *)(void *)ram;//在起始地址放置一个mem结构体mem->next = MEM_SIZE_ALIGNED;//下一个偏移量mem->prev = 0;//上一内存块为空mem->used = 0;//下一内存块为空/* initialize the end of the heap */ram_end = ptr_to_mem(MEM_SIZE_ALIGNED);ram_end->used = 1;//标记为已用ram_end->next = MEM_SIZE_ALIGNED;//下已内存块，指向自身ram_end->prev = MEM_SIZE_ALIGNED;//下已内存块，指向自身MEM_SANITY();/* initialize the lowest-free pointer to the start of the heap */lfree = (struct mem *)(void *)ram;MEM_STATS_AVAIL(avail, MEM_SIZE_ALIGNED);//获取内存状态if (sys_mutex_new(&mem_mutex) != ERR_OK) {LWIP_ASSERT("failed to create mem_mutex", 0);}
}

（2）内存申请

void *mem_malloc(mem_size_t size_in)
{mem_size_t ptr, ptr2, size;struct mem *mem, *mem2;
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXTu8_t local_mem_free_count = 0;
#endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */LWIP_MEM_ALLOC_DECL_PROTECT();if (size_in == 0) {return NULL;}/* Expand the size of the allocated memory region so that we canadjust for alignment. */size = (mem_size_t)LWIP_MEM_ALIGN_SIZE(size_in);if (size < MIN_SIZE_ALIGNED) {/* every data block must be at least MIN_SIZE_ALIGNED long */size = MIN_SIZE_ALIGNED;}
#if MEM_OVERFLOW_CHECKsize += MEM_SANITY_REGION_BEFORE_ALIGNED + MEM_SANITY_REGION_AFTER_ALIGNED;
#endifif ((size > MEM_SIZE_ALIGNED) || (size < size_in)) {return NULL;}/* protect the heap from concurrent access */sys_mutex_lock(&mem_mutex);LWIP_MEM_ALLOC_PROTECT();
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT/* run as long as a mem_free disturbed mem_malloc or mem_trim */do {local_mem_free_count = 0;
#endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT *//* Scan through the heap searching for a free block that is big enough,* beginning with the lowest free block.*/for (ptr = mem_to_ptr(lfree); ptr < MEM_SIZE_ALIGNED - size;ptr = ptr_to_mem(ptr)->next) {mem = ptr_to_mem(ptr);
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXTmem_free_count = 0;LWIP_MEM_ALLOC_UNPROTECT();/* allow mem_free or mem_trim to run */LWIP_MEM_ALLOC_PROTECT();if (mem_free_count != 0) {/* If mem_free or mem_trim have run, we have to restart since theycould have altered our current struct mem. */local_mem_free_count = 1;break;}
#endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */if ((!mem->used) &&(mem->next - (ptr + SIZEOF_STRUCT_MEM)) >= size) {/* mem is not used and at least perfect fit is possible:* mem->next - (ptr + SIZEOF_STRUCT_MEM) gives us the 'user data size' of mem */if (mem->next - (ptr + SIZEOF_STRUCT_MEM) >= (size + SIZEOF_STRUCT_MEM + MIN_SIZE_ALIGNED)) {/* (in addition to the above, we test if another struct mem (SIZEOF_STRUCT_MEM) containing* at least MIN_SIZE_ALIGNED of data also fits in the 'user data space' of 'mem')* -> split large block, create empty remainder,* remainder must be large enough to contain MIN_SIZE_ALIGNED data: if* mem->next - (ptr + (2*SIZEOF_STRUCT_MEM)) == size,* struct mem would fit in but no data between mem2 and mem2->next* @todo we could leave out MIN_SIZE_ALIGNED. We would create an empty*       region that couldn't hold data, but when mem->next gets freed,*       the 2 regions would be combined, resulting in more free memory*/ptr2 = (mem_size_t)(ptr + SIZEOF_STRUCT_MEM + size);LWIP_ASSERT("invalid next ptr",ptr2 != MEM_SIZE_ALIGNED);/* create mem2 struct */mem2 = ptr_to_mem(ptr2);mem2->used = 0;mem2->next = mem->next;mem2->prev = ptr;/* and insert it between mem and mem->next */mem->next = ptr2;mem->used = 1;if (mem2->next != MEM_SIZE_ALIGNED) {ptr_to_mem(mem2->next)->prev = ptr2;}MEM_STATS_INC_USED(used, (size + SIZEOF_STRUCT_MEM));} else {/* (a mem2 struct does no fit into the user data space of mem and mem->next will always* be used at this point: if not we have 2 unused structs in a row, plug_holes should have* take care of this).* -> near fit or exact fit: do not split, no mem2 creation* also can't move mem->next directly behind mem, since mem->next* will always be used at this point!*/mem->used = 1;MEM_STATS_INC_USED(used, mem->next - mem_to_ptr(mem));}
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
mem_malloc_adjust_lfree:
#endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */if (mem == lfree) {struct mem *cur = lfree;/* Find next free block after mem and update lowest free pointer */while (cur->used && cur != ram_end) {#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXTmem_free_count = 0;LWIP_MEM_ALLOC_UNPROTECT();/* prevent high interrupt latency... */LWIP_MEM_ALLOC_PROTECT();if (mem_free_count != 0) {/* If mem_free or mem_trim have run, we have to restart since theycould have altered our current struct mem or lfree. */goto mem_malloc_adjust_lfree;}
#endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */cur = ptr_to_mem(cur->next);}lfree = cur;LWIP_ASSERT("mem_malloc: !lfree->used", ((lfree == ram_end) || (!lfree->used)));}LWIP_MEM_ALLOC_UNPROTECT();sys_mutex_unlock(&mem_mutex);LWIP_ASSERT("mem_malloc: allocated memory not above ram_end.",(mem_ptr_t)mem + SIZEOF_STRUCT_MEM + size <= (mem_ptr_t)ram_end);LWIP_ASSERT("mem_malloc: allocated memory properly aligned.",((mem_ptr_t)mem + SIZEOF_STRUCT_MEM) % MEM_ALIGNMENT == 0);LWIP_ASSERT("mem_malloc: sanity check alignment",(((mem_ptr_t)mem) & (MEM_ALIGNMENT - 1)) == 0);#if MEM_OVERFLOW_CHECKmem_overflow_init_element(mem, size_in);
#endifMEM_SANITY();return (u8_t *)mem + SIZEOF_STRUCT_MEM + MEM_SANITY_OFFSET;}}
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT/* if we got interrupted by a mem_free, try again */} while (local_mem_free_count != 0);
#endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */MEM_STATS_INC(err);LWIP_MEM_ALLOC_UNPROTECT();sys_mutex_unlock(&mem_mutex);LWIP_DEBUGF(MEM_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("mem_malloc: could not allocate %"S16_F" bytes\n", (s16_t)size));return NULL;
}

Lwip协议详解（基于Lwip 2.1.0）-内存管理相关推荐

详解：物理地址，虚拟地址，内存管理，逻辑地址之间的关系
物理地址: 这里说的物理地址是内存中的内存单元实际地址,不是外部总线连接的其他电子元件的地址! 物理地址属于比较好理解的,物理地址就是内存中每个内存单元的编号,这个编号是顺序排好的,物理地址的大小决定 ...
Lwip协议详解（基于Lwip 2.1.0）-ICMP协议 (未完待续)
4.ICMP协议 4.1 原理 IP协议提供的是一种不可靠无连接的数据服务,在IP数据报被交互到最终目的主机的过程中,网络中每一个路由器都是自主运行,它们根据数据报中的目的IP地址为数据报选择的最佳路 ...
Lwip协议详解（基于Lwip 2.1.0）UDP协议（未完待续）
5.UDP协议 5.1 UDP的原理 UDP属于运输层协议,称为用户数据报协议,是一种无连接.不可靠的传输协议,它只在低级程度上实现了传输功能,UDP只简单地完成数据从一个进程到另一个进程的交付. 它 ...
MODBUS通讯协议详解(基于485)
参考:灵育科技Modbus课程总结作者:Naunyang 时间:2020-11-23 13:51:58 网址:https://blog.csdn.net/Naunyang/article/detai ...
SPI通讯协议详解基于STM32
SPI 协议简介 SPI 协议是由摩托罗拉公司提出的通讯协议 (Serial Peripheral Interface),即串行外围设备接口,是一种高速全双工的通信总线.它被广泛地使用在 ADC.L ...
java udp 协议_网络协议 - UDP 协议详解
¶ 网络协议 - UDP 协议详解基于TCP和UDP的协议非常广泛,所以也有必要对UDP协议进行详解.@pdai ¶ UDP概述 UDP(User Datagram Protocol)即用户数据报协 ...
HTTP 2.0 协议详解
HTTP 2.0 协议详解一.HTTP 2.0:改进传输性能 HTTP 2.0 的主要目标是改进传输性能,实现低延迟和高吞吐量.从另一方面看,HTTP 的高层协议语义并不会因为这次版本升级而受影响. ...
LwIP 之六详解动态内存管理内存池（memp.c/h）
该文主要是接上一部分LwIP 之详解动态内存管理内存堆(mem.c/h),该部分许多内容需要用到上一篇的内容.该部分主要是详细介绍LwIP中的动态内存池.整个内存池的实现相较于内存堆来说,还是 ...
LwIP 之六详解内存池（memp.c/h）动态内存管理策略
对于嵌入式开发来说,内存管理及使用是至关重要的,内存的使用多少.内存泄漏等时刻需要注意!合理的内存管理策略将从根本上决定内存分配和回收效率,最终决定系统的整体性能.LwIP 就提供了动态内存堆管 ...
LwIP 之五详解动态内存管理内存堆（mem.c/h）
写在前面目前网上有很多介绍LwIP内存的文章,但是绝大多数都不够详细,甚至很多介绍都是错误的!无论是代码的说明还是给出的图例,都欠佳!下面就从源代码,到图例详细进行说明. 目前,网络上多数文 ...

Lwip协议详解（基于Lwip 2.1.0）-内存管理

1、内存管理

Lwip协议详解（基于Lwip 2.1.0）-内存管理相关推荐

最新文章

热门文章