[置顶] linux内核启动2-setup_arch中的内存初始化（目前分析高端内存）

上一篇微博留下了这几个函数，现在我们来分析它们

        sanity_check_meminfo();

        arm_memblock_init(&meminfo, mdesc);

        paging_init(mdesc);

        request_standard_resources(mdesc);

在上一微博有展现根据启动参数初始化meminfo，记录了物理内存的开始和大小

sanity_check_meminfo();

有mmu的情况下这个函数才有意义，初始化高端内存，首先内核要选上这个

KernelFeatures下的

[*]High Memory Support

arch/arm/include/asm/setup.h

#ifdef CONFIG_ARCH_EP93XX

# define NR_BANKS 16

#else

#endif

struct membank {

phys_addr_t start;

unsigned longsize;

unsigned inthighmem;

};如果是高端内存highmem为1

struct meminfo {

int nr_banks;

struct membankbank[NR_BANKS];

};

extern struct meminfo meminfo;

我们现在的函数就是初始化meminfo这个全局变量

高端内存

linux内核的地址空间是3G~4G。假如说机器的内存为512M，那么内存的物

理地址范围是：0~512，而映射到内核空间的范围是3G~3G+512M（可以叫low memory).

＋512G～4G,但是为了避免越界等安全问题

的考虑，高端内存又离开了低端内存8M空间，即从3G＋512M+8M空间开始。linux内核又规定，高端内存至少为128M，即加入物理内存为1G，那么高端内存就是从896M~4G，即其最大地址：0xC0000000+896M,实际：0xC0000000+x(内存size)

简单举个例子，假设你有2G内存，而内核只有1G不能全部做线性映射，内核就会把前896M用于RAM线性映射，后128M可以通过更改映射关系访问剩下的内存。有三种方法：永久内核映射，临时映射，非连续内存分配（这些以后写关于内存管理的文章时再分析）。

没有全部贴

void __init sanity_check_meminfo(void)

{

int i, j, highmem= 0;

//wxl add

printk(KERN_NOTICE"vmalloc_min = %lx\n", vmalloc_min);

打印结果

vmalloc_min = ee000000

vmalloc_min = (void *)(VMALLOC_END - SZ_128M);

arch/arm/mach-s3c2410/include/mach/vmalloc.h
#define VMALLOC_END 0xF6000000UL

0xF6000000-0x8000000=0xEE000000

3808M

for (i = 0, j = 0;i < meminfo.nr_banks; i++) {

structmembank *bank = &meminfo.bank[j];

*bank =meminfo.bank[i];

#ifdef CONFIG_HIGHMEM

_va()是物理地址转换虚拟地址

#define __virt_to_phys(x)      ((x) - PAGE_OFFSET + PHYS_OFFSET)

#define __phys_to_virt(x)      ((x) - PHYS_OFFSET + PAGE_OFFSET)

#define __va(x)                ((void *)__phys_to_virt((unsigned long)(x)))

下面的条件告诉了我们高端地址范围，大于等于vmalloc_min的好理解，小于PAGE_OFFSET大概就是高端内存没有一次全部映射到内核空间，所以有低于PAGE_OFFSET的高端内存

if(__va(bank->start) >= vmalloc_min ||

__va(bank->start) < (void *) PAGE_OFFSET)

highmem = 1;

//wxl add

printk(KERN_NOTICE "start:bank->start = %lx bank->size = %lx __va = %lx highmem = %d\n",(unsigned long)bank->start, (unsigned long)bank->size, (unsignedlong)__va(bank->start), highmem);

打印结果

start: bank->start = 30000000 bank->size = 4000000 __va =c0000000 highmem = 0

bank->start bank->size就是上一篇微博提到的

bank->highmem = highmem;

/*

* Splitthose memory banks which are partially overlapping

* thevmalloc area greatly simplifying things later.

*/

 假设__va(bank->start) < vmalloc_min；它的大小可能会超过低端内存，也就是起始地址在低端，结束地址超过低端范围，那么就要把它分开，你可以简单看看代码

if(__va(bank->start) < vmalloc_min &&

bank->size > vmalloc_min - __va(bank->start)) {

if(meminfo.nr_banks >= NR_BANKS) {

printk(KERN_CRIT "NR_BANKS too low, "

"ignoringhigh 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);

}

//wxl add

printk(KERN_NOTICE "end: bank->start = %lx bank->size =%lx\n", (unsigned long)bank->start, (unsigned long)bank->size);

打印结果

end: bank->start = 30000000 bank->size = 4000000

#else

……

#endif

重设低端内存限制

if(!bank->highmem && bank->start + bank->size > lowmem_limit)

lowmem_limit =bank->start + bank->size;

j++;

}

……

未完待续,,,