关于rt-thread动态内存管理函数的实现有一个疑问求解答

我最近在看rt-thread的动态内存管理函数的实现，好像是从lwip哪里移植过来的，有一个疑问。

void rt_system_heap_init(void* begin_addr, void* end_addr)
{
    struct heap_mem *mem;
    /* alignment addr */
    begin_addr = (void*)RT_ALIGN((rt_uint32_t)begin_addr, RT_ALIGN_SIZE);
    /* calculate the aligned memory size */
    mem_size_aligned = RT_ALIGN((rt_uint32_t)end_addr - (rt_uint32_t)begin_addr, RT_ALIGN_SIZE) - 2 * sizeof(struct heap_mem);
    /* point to begin address of heap */
    heap_ptr = begin_addr;
#ifdef RT_MEM_DEBUG
    rt_kprintf("mem init, heap begin address 0x%x, size %d
", (rt_uint32_t)heap_ptr, mem_size_aligned);
#endif
    /* initialize the start of the heap */
    mem = (struct heap_mem *)heap_ptr;
    mem->magic= HEAP_MAGIC;
    mem->next = mem_size_aligned;
    mem->prev = 0;
    mem->used = 0;
    /* initialize the end of the heap */
    heap_end = (struct heap_mem *)&heap_ptr[mem_size_aligned];
    heap_end->magic= HEAP_MAGIC;
    heap_end->used = 1;
    heap_end->next = mem_size_aligned;
    heap_end->prev = mem_size_aligned;
    rt_sem_init(&heap_sem, "heap", 1, RT_IPC_FLAG_FIFO);
    /* initialize the lowest-free pointer to the start of the heap */
    lfree = (struct heap_mem *)heap_ptr;
}

我的理解是其中mem->next是mem的下一个内存管理块基于heap_ptr偏移值，而
mem_size_aligned = RT_ALIGN((rt_uint32_t)end_addr - (rt_uint32_t)begin_addr, RT_ALIGN_SIZE) - 2 * sizeof(struct heap_mem);
已经为头尾内存块管理结构留足了空间，所以mem_size_aligned应该是初始内存块实际可用的内存空间，如果mem->next = mem_size_aligned;那么初始内存块实际可用的内存只有mem_size_aligned-SIZEOF_STRUCT_MEM了，这样不是不合理吗？
所以我觉得应该写成下面这样的

void rt_system_heap_init(void* begin_addr, void* end_addr)
{
    struct heap_mem *mem;
    /* alignment addr */
    begin_addr = (void*)RT_ALIGN((rt_uint32_t)begin_addr, RT_ALIGN_SIZE);
    /* calculate the aligned memory size */
    mem_size_aligned = RT_ALIGN((rt_uint32_t)end_addr - (rt_uint32_t)begin_addr, RT_ALIGN_SIZE) - 2 * SIZEOF_STRUCT_MEM;
    /* point to begin address of heap */
    heap_ptr = begin_addr;
#ifdef RT_MEM_DEBUG
    rt_kprintf("mem init, heap begin address 0x%x, size %d
", (rt_uint32_t)heap_ptr, mem_size_aligned);
#endif
    /* initialize the start of the heap */
    mem = (struct heap_mem *)heap_ptr;
    mem->magic= HEAP_MAGIC;
    mem->next = mem_size_aligned+SIZEOF_STRUCT_MEM;
    mem->prev = 0;
    mem->used = 0;
    /* initialize the end of the heap */
    heap_end = (struct heap_mem *)&heap_ptr[mem->next];
    heap_end->magic= HEAP_MAGIC;
    heap_end->used = 1;
    heap_end->next = mem_size_aligned+SIZEOF_STRUCT_MEM;
    heap_end->prev = mem_size_aligned+SIZEOF_STRUCT_MEM;
    rt_sem_init(&heap_sem, "heap", 1, RT_IPC_FLAG_FIFO);
    /* initialize the lowest-free pointer to the start of the heap */
    lfree = (struct heap_mem *)heap_ptr;
}

同时将mem.c文件中的所有
if (mem2->next != mem_size_aligned)改为if (mem2->next != (mem_size_aligned+SIZEOF_STRUCT_MEM))

不知道这样理解对不对，希望哪位高人能帮忙解答一下。