mm_init分析(Zoned Buddy Allocator)

最新推荐文章于 2025-07-11 10:54:22 发布

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#command #数据结构 #struct #null #file

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本文分析了Linux内核启动过程中的关键函数start_kernel。该函数负责完成处理器架构初始化、内存管理初始化等工作，并涉及页框管理、物理内存释放等核心操作。

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1 mm_init分析

file:init/main.c

start_kernel函数

{

...

setup_arch(&command_line);

//处理器相关的初始化代码，paging_init,详细见bootmem_init分析
mm_init_owner(&init_mm, &init_task);
setup_command_line(command_line);
setup_nr_cpu_ids();
setup_per_cpu_areas();
smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */

build_all_zonelists(NULL);
page_alloc_init();

printk(KERN_NOTICE "Kernel command line: %s/n", boot_command_line);
parse_early_param();
parse_args("Booting kernel", static_command_line, __start___param,
__stop___param - __start___param,
&unknown_bootoption);
pidhash_init();
vfs_caches_init_early();
sort_main_extable();
trap_init();
mm_init();

//当启动初始化完后，node_bootmem_map会被释放，系统初始化mem_map,

//利用struct page数据结构来管理所有的内存。

...

}

mem_init->free_all_bootmem_node->free_all_bootmem_core

//释放node_bootmem_map，使用mem_map管理物理内存，以页框为单位

static unsigned long __init free_all_bootmem_core(bootmem_data_t *bdata)
{
int aligned;
struct page *page;
unsigned long start, end, pages, count = 0;

if (!bdata->node_bootmem_map)
return 0;

start = bdata->node_min_pfn;
end = bdata->node_low_pfn;

/*
* If the start is aligned to the machines wordsize, we might
* be able to free pages in bulks of that order.
*/
aligned = !(start & (BITS_PER_LONG - 1));

bdebug("nid=%td start=%lx end=%lx aligned=%d/n",
bdata - bootmem_node_data, start, end, aligned);

while (start < end) {
unsigned long *map, idx, vec;

  map = bdata->node_bootmem_map;
  idx = start - bdata->node_min_pfn;
  vec = ~map[idx / BITS_PER_LONG];

//查询改为是否为"0",当空闲时将page标志为PG_Reserved

if (aligned && vec == ~0UL && start + BITS_PER_LONG < end) {
int order = ilog2(BITS_PER_LONG);

   __free_pages_bootmem(pfn_to_page(start), order);
   count += BITS_PER_LONG;
  } else {
   unsigned long off = 0;

   while (vec && off < BITS_PER_LONG) {
    if (vec & 1) {
     page = pfn_to_page(start + off);
     __free_pages_bootmem(page, 0);
     count++;
    }
    vec >>= 1;
    off++;
   }
  }
  start += BITS_PER_LONG;
}

page = virt_to_page(bdata->node_bootmem_map);

//得到node_bootmem_map的page地址
pages = bdata->node_low_pfn - bdata->node_min_pfn;

//得到物理内存的页框数
pages = bootmem_bootmap_pages(pages);

//node_bootmem_map共占了( (pages/8)>>12 )页
count += pages;
while (pages--)
__free_pages_bootmem(page++, 0); //释放node_bootmem_map占用的页框

bdebug("nid=%td released=%lx/n", bdata - bootmem_node_data, count);

return count;
}

Author:Woodpecker <Pecker.hu@gmail.com>