分析free_all_bootmem_core

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

if (!bdata->node_bootmem_map)
return 0;

/*拿到开始结束页框*/
start = bdata->node_min_pfn;

end = bdata->node_low_pfn;

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

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

/*map为内存使用情况位图的页框指针， idx是当前要处理的页框序号，shift是4个字节<span style="font-family: Arial, Helvetica, sans-serif;">BITS_PER_LONG个二进制位内的偏移，就是idx序号所在的页使用情况的long型数据内的位偏移</span>*/
map = bdata->node_bootmem_map;
idx = start - bdata->node_min_pfn;
shift = idx & (BITS_PER_LONG - 1);
/*
* vec holds at most BITS_PER_LONG map bits,
* bit 0 corresponds to start.
*/

/*取出idx序号所在页的ulong型数据，并且取反， 位为1表示未使用页*/
vec = ~map[idx / BITS_PER_LONG];
/*假如当前页不是32（<span style="font-family: Arial, Helvetica, sans-serif;">BITS_PER_LONG</span>）的倍数，需要偏移，那么把当前页移动到vec最低位，并且从下一个数据补齐剩余的映射位，凑够32位一起处理*/
if (shift) {
vec >>= shift;
if (end - start >= BITS_PER_LONG)
vec |= ~map[idx / BITS_PER_LONG + 1] <<
(BITS_PER_LONG - shift);
}
/*
* If we have a properly aligned and fully unreserved
* BITS_PER_LONG block of pages in front of us, free
* it in one go.
*/

/*<span style="font-family: Arial, Helvetica, sans-serif;">IS_ALIGNED是判断start是否是BITS_PER_LONG的倍数， 相当于start % 32 == 0,  ver 都为1表示这32个页都是空闲的</span>*/
if (IS_ALIGNED(start, BITS_PER_LONG) && vec == ~0UL) {
int order = ilog2(BITS_PER_LONG);
/*释放这32页*/
__free_pages_bootmem(pfn_to_page(start), order);
count += BITS_PER_LONG;
start += BITS_PER_LONG;
} else {
unsigned long cur = start;
/*ALIGN（a，32）相当于（(a + 31)/32）*32, 就是a如正好能对齐到32就还是a,否则向上取对齐， 下面这句就是start/<span style="font-family: Arial, Helvetica, sans-serif;">BITS_PER_LONG + 1就是始终向上找个对齐的位置。 挨个遍历每一位</span><span style="font-family: Arial, Helvetica, sans-serif;">*/</span>
start = ALIGN(start + 1, BITS_PER_LONG);
while (vec && cur != start) {
if (vec & 1) {
page = pfn_to_page(cur);
__free_pages_bootmem(page, 0);
count++;
}
vec >>= 1;
++cur;
}
}
}
/*释放<span style="font-family: Arial, Helvetica, sans-serif;">bdata->node_bootmem_map指向的页</span><span style="font-family: Arial, Helvetica, sans-serif;">*/</span>
page = virt_to_page(bdata->node_bootmem_map);
pages = bdata->node_low_pfn - bdata->node_min_pfn;
pages = bootmem_bootmap_pages(pages);
count += pages;
while (pages--)
__free_pages_bootmem(page++, 0);

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

return count;
}

__free_pages_bootmem待续