Linux内存模型之bootmem分配器<二>

简介：介绍一下上文遗留的两个结构memblock以及meminfo.

相关阅读：http://www.linuxidc.com/Linux/2012-02/53139.htm 

**********************************

*  在arch/arm/kernel/setup.c中，
*  sanity_check_meminfo();

**********************************
arm_memblock_init(&meminfo, mdesc);

arch/arm/mm中，
void __init sanity_check_meminfo(void)
{
 int i, j, highmem = 0;

        //遍历所有的bank
 for (i = 0, j = 0; i < meminfo.nr_banks; i++) {
  struct membank *bank = &meminfo.bank[j];
  *bank = meminfo.bank[i];

#ifdef CONFIG_HIGHMEM
       //如果定义了高端内存，地址范围在高端内，则标记
  if (__va(bank->start) >= vmalloc_min ||
      __va(bank->start) < (void *)PAGE_OFFSET)
   highmem = 1;

  bank->highmem = highmem;       //标记

  /*
   * Split those memory banks which are partially overlapping
   * the vmalloc area greatly simplifying things later.
   */
                //范围在低端内存，但是size大于低端范围也就是
                //起始地址在低端，结束地址超过低端范围
  if (__va(bank->start) < vmalloc_min &&
      bank->size > vmalloc_min – __va(bank->start)) {
                        //banks号大于等于总数量，则直接忽略该bank
                        //否则将该bank分成两个bank，高端部分标记成高端
   if (meminfo.nr_banks >= NR_BANKS) {
    printk(KERN_CRIT “NR_BANKS too low, “
       “ignoring high memory\n”);
   } else {
    memmove(bank + 1, bank,
     (meminfo.nr_banks – i) * sizeof(*bank));
    meminfo.nr_banks++;
    i++;
    bank[1].size -= vmalloc_min – __va(bank->start);
    bank[1].start = __pa(vmalloc_min – 1) + 1;
    bank[1].highmem = highmem = 1;
    j++;
   }
   bank->size = vmalloc_min – __va(bank->start);
  }
#else
  bank->highmem = highmem;   //没定义就赋值为0

  /*
   * Check whether this memory bank would entirely overlap
   * the vmalloc area.
   */
                //没定义高端地址，那么高端部分全部忽略
  if (__va(bank->start) >= vmalloc_min ||
      __va(bank->start) < (void *)PAGE_OFFSET) {
   printk(KERN_NOTICE “Ignoring RAM at %.8llx-%.8llx “
          “(vmalloc region overlap).\n”,
          (unsigned long long)bank->start,
          (unsigned long long)bank->start + bank->size – 1);
   continue;
  }

  /*
   * Check whether this memory bank would partially overlap
   * the vmalloc area.
   */
  if (__va(bank->start + bank->size) > vmalloc_min ||
      __va(bank->start + bank->size) < __va(bank->start)) {
   unsigned long newsize = vmalloc_min – __va(bank->start);
   printk(KERN_NOTICE “Truncating RAM at %.8llx-%.8llx “
          “to -%.8llx (vmalloc region overlap).\n”,
          (unsigned long long)bank->start,
          (unsigned long long)bank->start + bank->size – 1,
          (unsigned long long)bank->start + newsize – 1);
   bank->size = newsize;
  }
#endif
  if (!bank->highmem && bank->start + bank->size > lowmem_limit)
   lowmem_limit = bank->start + bank->size;

  j++;
 }
#ifdef CONFIG_HIGHMEM
        //如果是高端内存，还要进行进一步支持的确认，vipt的不支持
 if (highmem) {
  const char *reason = NULL;

  if (cache_is_vipt_aliasing()) {
   /*
    * Interactions between kmap and other mappings
    * make highmem support with aliasing VIPT caches
    * rather difficult.
    */
   reason = “with VIPT aliasing cache”;
  }
  if (reason) {
   printk(KERN_CRIT “HIGHMEM is not supported %s, ignoring high memory\n”,
    reason);
   while (j > 0 && meminfo.bank[j – 1].highmem)
    j–;
  }
 }
#endif
 meminfo.nr_banks = j;
 memblock_set_current_limit(lowmem_limit);
}

这里其中vmalloc_vin 定义为static void * __initdata vmalloc_min = (void *)(VMALLOC_END – SZ_128M);
而vmalloc_end在2440上定义为arch/arm/mach-s3c2410/include/mach/vmalloc.h
#define VMALLOC_END 0xF6000000UL

…
if (mdesc->fixup)            //一种方法，可惜2440没有
  mdesc->fixup(tags, &from, &meminfo);

 if (tags->hdr.tag == ATAG_CORE) {
  if (meminfo.nr_banks != 0)
   squash_mem_tags(tags);
  save_atags(tags);
  parse_tags(tags);        //另一个地方
 }
…

跟进去最终会到这里
/*
 * Scan the tag table for this tag, and call its parse function.
 * The tag table is built by the linker from all the __tagtable
 * declarations.
 */
static int __init parse_tag(const struct tag *tag)
{
 extern struct tagtable __tagtable_begin, __tagtable_end;
 struct tagtable *t;

 for (t = &__tagtable_begin; t < &__tagtable_end; t++)
  if (tag->hdr.tag == t->tag) {
   t->parse(tag);
   break;
  }

 return t < &__tagtable_end;
}

__tagtable_begin同样单独的一个段，定义在arch/arm/vmlinux.lds，
__arch_info_begin = .;
            *(.arch.info)
        __arch_info_end = .;
        __tagtable_begin = .;
            *(.taglist)
        __tagtable_end = .;
            *(.data.init)
        . = ALIGN(16);
其中同文件下
tatic int __init parse_tag_mem32(const struct tag *tag)
{
 return arm_add_memory(tag->u.mem.start, tag->u.mem.size);
}

__tagtable(ATAG_MEM, parse_tag_mem32);

又有
#define __tag __used __attribute__((__section__(“.taglist.init”)))
#define __tagtable(tag, fn) \
static const struct tagtable __tagtable_##fn __tag = { tag, fn }

可见parse_tag_mem32就被定义于这个段，那么就会调用它，跟进去又会调用arm_add_memory(tag->u.mem.start, tag->u.mem.size);这个是我们的重点函数，会把参数列表传递过来的内存信息对齐后打包到meminfo，找到了meminfo怎么来的，回来再继续看刚才剩下的一个函数，arm_memblock_init(&meminfo, mdesc);这个函数比较简单，这里就不贴出来了，主要是把刚才得到的内存布局中已经使用的部分标记出来比如kernel占用部分，异常表占用部分等等…

总结：分析了上文遗留的两个结构memblock以及meminfo，bootmem结构到现在应当很清晰了，下文会简单分析下具体的bootmem的分配内存
函数 ^.^!