前面构建内存管理框架，已经将内存管理node节点设置完毕，接下来将是管理区和页面管理的构建。此处代码实现主要在于setup_arch()下的一处钩子：x86_init.paging.pagetable_init()。据前面分析可知x86_init结构体内该钩子实际上挂接的是native_pagetable_init()函数。
native_pagetable_init()
【file：/arch/x86/mm/init_32.c】
void __init native_pagetable_init(void)
{
unsigned long pfn, va;
pgd_t *pgd, *base = swapper_pg_dir;
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
/*
* Remove any mappings which extend past the end of physical
* memory from the boot time page table.
* In virtual address space, we should have at least two pages
* from VMALLOC_END to pkmap or fixmap according to VMALLOC_END
* definition. And max_low_pfn is set to VMALLOC_END physical
* address. If initial memory mapping is doing right job, we
* should have pte used near max_low_pfn or one pmd is not present.
*/
for (pfn = max_low_pfn; pfn < 1<<(32-PAGE_SHIFT); pfn++) {
va = PAGE_OFFSET + (pfn<<PAGE_SHIFT);
pgd = base + pgd_index(va);
if (!pgd_present(*pgd))
break;
pud = pud_offset(pgd, va);
pmd = pmd_offset(pud, va);
if (!pmd_present(*pmd))
break;
/* should not be large page here */
if (pmd_large(*pmd)) {
pr_warn("try to clear pte for ram above max_low_pfn: pfn: %lx pmd: %p pmd phys: %lx, but pmd is big page and is not using pte !\n",
pfn, pmd, __pa(pmd));
BUG_ON(1);
}
pte = pte_offset_kernel(pmd, va);
if (!pte_present(*pte))
break;
printk(KERN_DEBUG "clearing pte for ram above max_low_pfn: pfn: %lx pmd: %p pmd phys: %lx pte: %p pte phys: %lx\n",
pfn, pmd, __pa(pmd), pte, __pa(pte));
pte_clear(NULL, va, pte);
}
paravirt_alloc_pmd(&init_mm, __pa(base) >> PAGE_SHIFT);
paging_init();
}
该函数的for循环主要是用于检测max_low_pfn直接映射空间后面的物理内存是否存在系统启动引导时创建的页表，如果存在，则使用pte_clear()将其清除。
接下来的paravirt_alloc_pmd()主要是用于准虚拟化，主要是使用钩子函数的方式替换x86环境中多种多样的指令实现。
再往下的paging_init()：
【file：/arch/x86/mm/init_32.c】
/*
* paging_init() sets up the page tables - note that the first 8MB are
* already mapped by head.S.
*
* This routines also unmaps the page at virtual kernel address 0, so
* that we can trap those pesky NULL-reference errors in the kernel.
*/
void __init paging_init(void)
{
pagetable_init();
__flush_tlb_all();
kmap_init();
/*
* NOTE: at this point the bootmem allocator is fully available.
*/
olpc_dt_build_devicetree();
sparse_memory_present_with_active_regions(MAX_NUMNODES);
sparse_init();
zone_sizes_init();
}
paging_init()主要都是函数调用，现在逐一分析各个函数功能，先看pagetable_init()：
【file：/arch/x86/mm/init_32.c】
static void __init pagetable_init(void)
{
pgd_t *pgd_base = swapper_pg_dir;
permanent_kmaps_init(pgd_base);
}
这里再次看到页全局目录swapper_pg_dir变量，它作为参数接着调用permanent_kmaps_init()：
【file：/arch/x86/mm/init_32.c】
static void __init permanent_kmaps_init(pgd_t *pgd_base)
{
unsigned long vaddr;
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
vaddr = PKMAP_BASE;
page_table_range_init(vaddr, vaddr + PAGE_SIZE*LAST_PKMAP, pgd_base);
pgd = swapper_pg_dir + pgd_index(vaddr);
pud = pud_offset(pgd, vaddr);
pmd = pmd_offset(pud, vaddr);
pte = pte_offset_kernel(pmd, vaddr);
pkmap_page_table = pte;
}
这里可以看到前面分析过的建立页表函数page_table_range_init()，此处建立页表范围为PKMAP_BASE到PKMAP_BASE + PAGE_SIZE*LAST_PKMAP，这是KMAP区（永久映射区）的范围。继而也就是说当前是在建立永久映射区的页表，建好页表后将页表地址给永久映射区页表变量pkmap_page_table置值。
完了接着看paging_init()里面调用的下一个函数kmap_init()：
【file：/arch/x86/mm/init_32.c】
static void __init kmap_init(void)
{
unsigned long kmap_vstart;
/*
* Cache the first kmap pte:
*/
kmap_vstart = __fix_to_virt(FIX_KMAP_BEGIN);
kmap_pte = kmap_get_fixmap_pte(kmap_vstart);
kmap_prot = PAGE_KERNEL;
}
其中kmap_get_fixmap_pte()：
【file：/arch/x86/mm/init_32.c】
static inline pte_t *kmap_get_fixmap_pte(unsigned long vaddr)
{
return pte_offset_kernel(pmd_offset(pud_offset(pgd_offset_k(vaddr),
vaddr), vaddr), vaddr);
}
可以很容易看到kmap_init()主要是获取到临时映射区间的起始页表并往临时映射页表变量kmap_pte置值，并置页表属性kmap_prot为PAGE_KERNEL。
paging_init()中，由于没有开启CONFIG_OLPC配置，故olpc_dt_build_devicetree()为空函数，暂不分析。同样，前面提及的sparse_memory_present_with_active_regions()和sparse_init()也暂不分析。
最后看一下zone_sizes_init()：
【file：/arch/x86/mm/init.c】
void __init zone_sizes_init(void)
{
unsigned long max_zone_pfns[MAX_NR_ZONES];
memset(max_zone_pfns, 0, sizeof(max_zone_pfns));
#ifdef CONFIG_ZONE_DMA
max_zone_pfns[ZONE_DMA] = MAX_DMA_PFN;
#endif
#ifdef CONFIG_ZONE_DMA32
max_zone_pfns[ZONE_DMA32] = MAX_DMA32_PFN;
#endif
max_zone_pfns[ZONE_NORMAL] = max_low_pfn;
#ifdef CONFIG_HIGHMEM
max_zone_pfns[ZONE_HIGHMEM] = max_pfn;
#endif
free_area_init_nodes(max_zone_pfns);
}
通过max_zone_pfns获取各个管理区的最大页面数，并作为参数调用free_area_init_nodes(),其中free_area_init_nodes()函数实现:
【file：/mm/page_alloc.c】
/**
* free_area_init_nodes - Initialise all pg_data_t and zone data
* @max_zone_pfn: an array of max PFNs for each zone
*
* This will call free_area_init_node() for each active node in the system.
* Using the page ranges provided by add_active_range(), the size of each
* zone in each node and their holes is calculated. If the maximum PFN
* between two adjacent zones match, it is assumed that the zone is empty.
* For example, if arch_max_dma_pfn == arch_max_dma32_pfn, it is assumed
* that arch_max_dma32_pfn has no pages. It is also assumed that a zone
* starts where the previous one ended. For example, ZONE_DMA32 starts
* at arch_max_dma_pfn.
*/
void __init free_area_init_nodes(unsigned long *max_zone_pfn)
{
unsigned long start_pfn, end_pfn;
int i, nid;
/* Record where the zone boundaries are */
memset(arch_zone_lowest_possible_pfn, 0,
sizeof(arch_zone_lowest_possible_pfn));
memset(arch_zone_highest_possible_pfn, 0,
sizeof(arch_zone_highest_possible_pfn));
arch_zone_lowest_possible_pfn[0] = find_min_pfn_with_active_regions();
arch_zone_highest_possible_pfn[0] = max_zone_pfn[0];
for (i = 1; i < MAX_NR_ZONES; i++) {
if (i == ZONE_MOVABLE)
continue;
arch_zone_lowest_possible_pfn[i] =
arch_zone_highest_possible_pfn[i-1];
arch_zone_highest_possible_pfn[i] =
max(max_zone_pfn[i], arch_zone_lowest_possible_pfn[i]);
}
arch_zone_lowest_possible_pfn[ZONE_MOVABLE] = 0;
arch_zone_highest_possible_pfn[ZONE_MOVABLE] = 0;
/* Find the PFNs that ZONE_MOVABLE begins at in each node */
memset(zone_movable_pfn, 0, sizeof(zone_movable_pfn));
find_zone_movable_pfns_for_nodes();
/* Print out the zone ranges */
printk("Zone ranges:\n");
for (i = 0; i < MAX_NR_ZONES; i++) {
if (i == ZONE_MOVABLE)
continue;
printk(KERN_CONT " %-8s ", zone_names[i]);
if (arch_zone_lowest_possible_pfn[i] ==
arch_zone_highest_possible_pfn[i])
printk(KERN_CONT "empty\n");
else
printk(KERN_CONT "[mem %0#10lx-%0#10lx]\n",
arch_zone_lowest_possible_pfn[i] << PAGE_SHIFT,
(arch_zone_highest_possible_pfn[i]
<< PAGE_SHIFT) - 1);
}
/* Print out the PFNs ZONE_MOVABLE begins at in each node */
printk("Movable zone start for each node\n");
for (i = 0; i < MAX_NUMNODES; i++) {
if (zone_movable_pfn[i])
printk(" Node %d: %#010lx\n", i,
zone_movable_pfn[i] << PAGE_SHIFT);
}
/* Print out the early node map */
printk("Early memory node ranges\n");
for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid)
printk(" node %3d: [mem %#010lx-%#010lx]\n", nid,
start_pfn << PAGE_SHIFT, (end_pfn << PAGE_SHIFT) - 1);
/* Initialise every node */
mminit_verify_pageflags_layout();
setup_nr_node_ids();
for_each_online_node(nid) {
pg_data_t *pgdat = NODE_DATA(nid);
free_area_init_node(nid, NULL,
find_min_pfn_for_node(nid), NULL);
/* Any memory on that node */
if (pgdat->node_present_pages)
node_set_state(nid, N_MEMORY);
check_for_memory(pgdat, nid);
}
}
该函数中，arch_zone_lowest_possible_pfn用于存储各内存管理区可使用的最小内存页框号，而arch_zone_highest_possible_pfn则是用来存储各内存管理区可使用的最大内存页框号。于是find_min_pfn_with_active_regions()函数主要是实现用于获取最小内存页框号，而获取最大内存页框号则是紧随的for循环：
for (i = 1; i < MAX_NR_ZONES; i++) {
if (i == ZONE_MOVABLE)
continue;
arch_zone_lowest_possible_pfn[i] =
arch_zone_highest_possible_pfn[i-1];
arch_zone_highest_possible_pfn[i] =
max(max_zone_pfn[i], arch_zone_lowest_possible_pfn[i]);
}
该循环里面除了确定各内存管理区最大内存页框号，同时也确定了各管理区的最小内存页框号,实际上就是确定各个管理区的上下边界。此外，还有一个全局数组zone_movable_pfn，用于记录各个node节点的Movable管理区的起始页框号，而查找该页框号的相应函数为find_zone_movable_pfns_for_nodes()。
具体实现：
【file：/mm/page_alloc.c】
/*
* Find the PFN the Movable zone begins in each node. Kernel memory
* is spread evenly between nodes as long as the nodes have enough
* memory. When they don't, some nodes will have more kernelcore than
* others
*/
static void __init find_zone_movable_pfns_for_nodes(void)
{
int i, nid;
unsigned long usable_startpfn;
unsigned long kernelcore_node, kernelcore_remaining;
/* save the state before borrow the nodemask */
nodemask_t saved_node_state = node_states[N_MEMORY];
unsigned long totalpages = early_calculate_totalpages();
int usable_nodes = nodes_weight(node_states[N_MEMORY]);
struct memblock_type *type = &memblock.memory;
/* Need to find movable_zone earlier when movable_node is specified. */
find_usable_zone_for_movable();
/*
* If movable_node is specified, ignore kernelcore and movablecore
* options.
*/
if (movable_node_is_enabled()) {
for (i = 0; i < type->cnt; i++) {
if (!memblock_is_hotpluggable(&type->regions[i]))
continue;
nid = type->regions[i].nid;
usable_startpfn = PFN_DOWN(type->regions[i].base);
zone_movable_pfn[nid] = zone_movable_pfn[nid] ?
min(usable_startpfn, zone_movable_pfn[nid]) :
usable_startpfn;
}
goto out2;
}
/*
* If movablecore=nn[KMG] was specified, calculate what size of
* kernelcore that corresponds so that memory usable for
* any allocation type is evenly spread. If both kernelcore
* and movablecore are specified, then the value of kernelcore
* will be used for required_kernelcore if it's greater than
* what movablecore would have allowed.
*/
if (required_movablecore) {
unsigned long corepages;
/*
* Round-up so that ZONE_MOVABLE is at least as large as what
* was requested by the user
*/
required_movablecore =
roundup(required_movablecore, MAX_ORDER_NR_PAGES);
corepages = totalpages - required_movablecore;
required_kernelcore = max(required_kernelcore, corepages);
}
/* If kernelcore was not specified, there is no ZONE_MOVABLE */
if (!required_kernelcore)
goto out;
/* usable_startpfn is the lowest possible pfn ZONE_MOVABLE can be at */
usable_startpfn = arch_zone_lowest_possible_pfn[movable_zone];
restart:
/* Spread kernelcore memory as evenly as possible throughout nodes */
kernelcore_node = required_kernelcore / usable_nodes;
for_each_node_state(nid, N_MEMORY) {
unsigned long start_pfn, end_pfn;
/*
* Recalculate kernelcore_node if the division per node
* now exceeds what is necessary to satisfy the requested
* amount of memory for the kernel
*/
if (required_kernelcore < kernelcore_node)
kernelcore_node = required_kernelcore / usable_nodes;
/*
* As the map is walked, we track how much memory is usable
* by the kernel using kernelcore_remaining. When it is
* 0, the rest of the node is usable by ZONE_MOVABLE
*/
kernelcore_remaining = kernelcore_node;
/* Go through each range of PFNs within this node */
for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, NULL) {
unsigned long size_pages;
start_pfn = max(start_pfn, zone_movable_pfn[nid]);
if (start_pfn >= end_pfn)
continue;
/* Account for what is only usable for kernelcore */
if (start_pfn < usable_startpfn) {
unsigned long kernel_pages;
kernel_pages = min(end_pfn, usable_startpfn)
- start_pfn;
kernelcore_remaining -= min(kernel_pages,
kernelcore_remaining);
required_kernelcore -= min(kernel_pages,
required_kernelcore);
/* Continue if range is now fully accounted */
if (end_pfn <= usable_startpfn) {
/*
* Push zone_movable_pfn to the end so
* that if we have to rebalance
* kernelcore across nodes, we will
* not double account here
*/
zone_movable_pfn[nid] = end_pfn;
continue;
}
start_pfn = usable_startpfn;
}
/*
* The usable PFN range for ZONE_MOVABLE is from
* start_pfn->end_pfn. Calculate size_pages as the
* number of pages used as kernelcore
*/
size_pages = end_pfn - start_pfn;
if (size_pages > kernelcore_remaining)
size_pages = kernelcore_remaining;
zone_movable_pfn[nid] = start_pfn + size_pages;
/*
* Some kernelcore has been met, update counts and
* break if the kernelcore for this node has been
* satisfied
*/
required_kernelcore -= min(required_kernelcore,
size_pages);
kernelcore_remaining -= size_pages;
if (!kernelcore_remaining)
break;
}
}
/*
* If there is still required_kernelcore, we do another pass with one
* less node in the count. This will push zone_movable_pfn[nid] further
* along on the nodes that still have memory until kernelcore is
* satisfied
*/
usable_nodes--;
if (usable_nodes && required_kernelcore > usable_nodes)
goto restart;
out2:
/* Align start of ZONE_MOVABLE on all nids to MAX_ORDER_NR_PAGES */
for (nid = 0; nid < MAX_NUMNODES; nid++)
zone_movable_pfn[nid] =
roundup(zone_movable_pfn[nid], MAX_ORDER_NR_PAGES);
out:
/* restore the node_state */
node_states[N_MEMORY] = saved_node_state;
}
该函数中early_calculate_totalpages()主要用于统计系统页面总数，而nodes_weight()则是将当前系统的节点数统计返回，其入参node_states[N_MEMORY]的定义在page_alloc.c中：
nodemask_t node_states[NR_NODE_STATES] __read_mostly = {
[N_POSSIBLE] = NODE_MASK_ALL,
[N_ONLINE] = { { [0] = 1UL } },
#ifndef CONFIG_NUMA
[N_NORMAL_MEMORY] = { { [0] = 1UL } },
#ifdef CONFIG_HIGHMEM
[N_HIGH_MEMORY] = { { [0] = 1UL } },
#endif
#ifdef CONFIG_MOVABLE_NODE
[N_MEMORY] = { { [0] = 1UL } },
#endif
[N_CPU] = { { [0] = 1UL } },
#endif /* NUMA */
};
EXPORT_SYMBOL(node_states);
接着往下的find_usable_zone_for_movable()：
【file：/mm/page_alloc.c】
/*
* This finds a zone that can be used for ZONE_MOVABLE pages. The
* assumption is made that zones within a node are ordered in monotonic
* increasing memory addresses so that the "highest" populated zone is used
*/
static void __init find_usable_zone_for_movable(void)
{
int zone_index;
for (zone_index = MAX_NR_ZONES - 1; zone_index >= 0; zone_index--) {
if (zone_index == ZONE_MOVABLE)
continue;
if (arch_zone_highest_possible_pfn[zone_index] >
arch_zone_lowest_possible_pfn[zone_index])
break;
}
VM_BUG_ON(zone_index == -1);
movable_zone = zone_index;
}
其主要实现查找一个可用于ZONE_MOVABLE页面的内存管理区，该区低于ZONE_MOVABLE且页面数不为0。通常最高内存管理区被找到，然后管理区索引记录在全局变量movable_zone中。
接下来的if分支：
if (movable_node_is_enabled()) {
for (i = 0; i < type->cnt; i++) {
if (!memblock_is_hotpluggable(&type->regions[i]))
continue;
nid = type->regions[i].nid;
usable_startpfn = PFN_DOWN(type->regions[i].base);
zone_movable_pfn[nid] = zone_movable_pfn[nid] ?
min(usable_startpfn, zone_movable_pfn[nid]) :
usable_startpfn;
}
goto out2;
}
该分支主要是当movable_node已经设置的情况下，忽略kernelcore和movablecore的设置，找到最高内存管理区的起始页usable_startpfn和Movable管理区的页框号。
再往下的if分支：
if (required_movablecore) {
unsigned long corepages;
required_movablecore =
roundup(required_movablecore, MAX_ORDER_NR_PAGES);
corepages = totalpages – required_movablecore;
required_kernelcore = max(required_kernelcore, corepages);
}
该分支是当movablecore设置时，尽可能满足movablecore的设置情况下计算kernelcore的剩余空间大小，但如果kernelcore也设置时，则优先满足kernelcore的设置。
接着的：
if (!required_kernelcore)
goto out;
如果至此kernelcore仍未设置时，则表示其实movable管理区是不存在的。
最后在restart的标签内的代码，其主要实现的是将kernelcore的内存平均分配到各个node上面。其中局部变量kernelcore_node表示各个nodes平均分摊到的内存页面数，usable_startpfn表示movable管理区的最低内存页框号，主要通过遍历node_states[N_MEMORY]中标志可用的node节点并遍历节点内的各个内存块信息，将均摊的内存页面数分到各个node当中，如果无法均摊时，通过判断：
if (usable_nodes && required_kernelcore > usable_nodes)
goto restart;
重新再次平均分摊，基于优先满足kernelcore的设置前提，直至无法满足条件为止。
而在out2的标签内的代码则是用于将movable管理区的起始地址做MAX_ORDER_NR_PAGES对齐操作。
末尾out的标签则仅是恢复node_states[]而已。
find_zone_movable_pfns_for_nodes()函数虽然分析了这么多，但个人实验环境由于required_movablecore和required_kernelcore为0，故仅分析这么多了。
下面回到free_area_init_nodes()函数中。跟随在find_zone_movable_pfns_for_nodes()后面是一段日志信息内容打印，分别打印管理区范围信息（dmesg命令可以查看），个人实验环境上的信息为：
再往下的mminit_verify_pageflags_layout()函数主要用于内存初始化调测使用的，由于未开启CONFIG_DEBUG_MEMORY_INIT配置项，此函数为空。而setup_nr_node_ids()是用于设置内存节点总数的，此处如果最大节点数MAX_NUMNODES不超过1，则是空函数。
free_area_init_nodes()函数末了还有一个遍历各个节点做初始化的操作，暂且留待后面再分析。