在前面我们讨论了内存节点node_mem_map成员的初始化。了解到此成员其实是以struct page为单位的数组，数组大小跟此节点内存大小相关，那么这些描述符是何时初始化
呢，当前主要是在mem_init函数进行设置。
start_kernel() --> mm_init --> mem_init()
需要注意的是mem_init是跟体系结构相关的函数，比如针对ARM64的实现函数：
/*
* mem_init() marks the free areas in the mem_map and tells us how much memory
* is free. This is done after various parts of the system have claimed their
* memory after the kernel image.
*/
void __init mem_init(void)
{
if (swiotlb_force == SWIOTLB_FORCE ||
max_pfn > (arm64_dma_phys_limit >> PAGE_SHIFT))
swiotlb_init(1);
else
swiotlb_force = SWIOTLB_NO_FORCE;
这一步是设置最大的pfn号，超出这个最大的pfn是无效的。
set_max_mapnr(pfn_to_page(max_pfn) - mem_map);
#ifndef CONFIG_SPARSEMEM_VMEMMAP
free_unused_memmap();
#endif
下面这一步非常非常非常非常非常重要，其把启动过程中所有空闲内存释放到伙伴系统中去。 /* this will put all unused low memory onto the freelists */ free_all_bootmem();
mem_init_print_info(NULL); 打印一些信息。
#define MLK(b, t) b, t, ((t) - (b)) >> 10
#define MLM(b, t) b, t, ((t) - (b)) >> 20
#define MLG(b, t) b, t, ((t) - (b)) >> 30
#define MLK_ROUNDUP(b, t) b, t, DIV_ROUND_UP(((t) - (b)), SZ_1K)
pr_notice("Virtual kernel memory layout:\n");
#ifdef CONFIG_KASAN
pr_notice(" kasan : 0x%16lx - 0x%16lx (%6ld GB)\n",
MLG(KASAN_SHADOW_START, KASAN_SHADOW_END));
#endif
pr_notice(" modules : 0x%16lx - 0x%16lx (%6ld MB)\n",
MLM(MODULES_VADDR, MODULES_END));
pr_notice(" vmalloc : 0x%16lx - 0x%16lx (%6ld GB)\n",
MLG(VMALLOC_START, VMALLOC_END));
pr_notice(" .text : 0x%p" " - 0x%p" " (%6ld KB)\n",
MLK_ROUNDUP(_text, _etext));
pr_notice(" .rodata : 0x%p" " - 0x%p" " (%6ld KB)\n",
MLK_ROUNDUP(__start_rodata, __init_begin));
pr_notice(" .init : 0x%p" " - 0x%p" " (%6ld KB)\n",
MLK_ROUNDUP(__init_begin, __init_end));
pr_notice(" .data : 0x%p" " - 0x%p" " (%6ld KB)\n",
MLK_ROUNDUP(_sdata, _edata));
pr_notice(" .bss : 0x%p" " - 0x%p" " (%6ld KB)\n",
MLK_ROUNDUP(__bss_start, __bss_stop));
pr_notice(" fixed : 0x%16lx - 0x%16lx (%6ld KB)\n",
MLK(FIXADDR_START, FIXADDR_TOP));
pr_notice(" PCI I/O : 0x%16lx - 0x%16lx (%6ld MB)\n",
MLM(PCI_IO_START, PCI_IO_END));
#ifdef CONFIG_SPARSEMEM_VMEMMAP
pr_notice(" vmemmap : 0x%16lx - 0x%16lx (%6ld GB maximum)\n",
MLG(VMEMMAP_START, VMEMMAP_START + VMEMMAP_SIZE));
pr_notice(" 0x%16lx - 0x%16lx (%6ld MB actual)\n",
MLM((unsigned long)phys_to_page(memblock_start_of_DRAM()),
(unsigned long)virt_to_page(high_memory)));
#endif
pr_notice(" memory : 0x%16lx - 0x%16lx (%6ld MB)\n",
MLM(__phys_to_virt(memblock_start_of_DRAM()),
(unsigned long)high_memory));
#undef MLK
#undef MLM
#undef MLK_ROUNDUP
/*
* Check boundaries twice: Some fundamental inconsistencies can be
* detected at build time already.
*/
#ifdef CONFIG_COMPAT
BUILD_BUG_ON(TASK_SIZE_32 > TASK_SIZE_64);
#endif
/*
* Make sure we chose the upper bound of sizeof(struct page)
* correctly.
*/
BUILD_BUG_ON(sizeof(struct page) > (1 << STRUCT_PAGE_MAX_SHIFT));
if (PAGE_SIZE >= 16384 && get_num_physpages() <= 128) {
extern int sysctl_overcommit_memory;
/*
* On a machine this small we won't get anywhere without
* overcommit, so turn it on by default.
*/
sysctl_overcommit_memory = OVERCOMMIT_ALWAYS;
}
}
unsigned long __init free_all_bootmem(void)
{
unsigned long total_pages = 0;
bootmem_data_t *bdata;
reset_all_zones_managed_pages();
list_for_each_entry(bdata, &bdata_list, list)
total_pages += free_all_bootmem_core(bdata);
totalram_pages += total_pages;
return total_pages;
}
static unsigned long __init free_all_bootmem_core(bootmem_data_t *bdata)
{
struct page *page;
unsigned long *map, start, end, pages, cur, count = 0;
if (!bdata->node_bootmem_map)
return 0;
map = bdata->node_bootmem_map;
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 idx, vec;
unsigned shift;
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.
*/
vec = ~map[idx / BITS_PER_LONG];
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.
*/
if (IS_ALIGNED(start, BITS_PER_LONG) && vec == ~0UL) {
int order = ilog2(BITS_PER_LONG);
__free_pages_bootmem(pfn_to_page(start), start, order);
count += BITS_PER_LONG;
start += BITS_PER_LONG;
} else {
cur = start;
start = ALIGN(start + 1, BITS_PER_LONG);
while (vec && cur != start) {
if (vec & 1) {
page = pfn_to_page(cur);
__free_pages_bootmem(page, cur, 0);
count++;
}
vec >>= 1;
++cur;
}
}
}
cur = bdata->node_min_pfn;
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++, cur++, 0);
bdata->node_bootmem_map = NULL;
bdebug("nid=%td released=%lx\n", bdata - bootmem_node_data, count);
return count;
}
void __init __free_pages_bootmem(struct page *page, unsigned long pfn,
unsigned int order)
{
if (early_page_uninitialised(pfn))
return;
return __free_pages_boot_core(page, order);
}
static void __init __free_pages_boot_core(struct page *page, unsigned int order)
{
unsigned int nr_pages = 1 << order;
struct page *p = page;
unsigned int loop;
prefetchw(p);
for (loop = 0; loop < (nr_pages - 1); loop++, p++) {
prefetchw(p + 1);
__ClearPageReserved(p);
set_page_count(p, 0);
}
__ClearPageReserved(p);
set_page_count(p, 0);
page_zone(page)->managed_pages += nr_pages;
set_page_refcounted(page);
__free_pages(page, order);
}
下面就是通用流程处理了，即对页释放处理。
void __free_pages(struct page *page, unsigned int order)
{
if (put_page_testzero(page)) {
if (order == 0)
free_hot_cold_page(page, false);
else
__free_pages_ok(page, order);
}
}
EXPORT_SYMBOL(__free_pages);
