[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
# define NR_BANKS 8 三星当然是8
#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).
而其余的空间都是高端内存的范围,即：3＋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,,,
