mm/page_ext.c - third_party/linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 #include <linux/mm.h>
 #include <linux/mmzone.h>
 #include <linux/memblock.h>
 #include <linux/page_ext.h>
 #include <linux/memory.h>
 #include <linux/vmalloc.h>
 #include <linux/kmemleak.h>
 #include <linux/page_owner.h>
 #include <linux/page_idle.h>

 /*
  * struct page extension
  *
  * This is the feature to manage memory for extended data per page.
  *
  * Until now, we must modify struct page itself to store extra data per page.
  * This requires rebuilding the kernel and it is really time consuming process.
  * And, sometimes, rebuild is impossible due to third party module dependency.
  * At last, enlarging struct page could cause un-wanted system behaviour change.
  *
  * This feature is intended to overcome above mentioned problems. This feature
  * allocates memory for extended data per page in certain place rather than
  * the struct page itself. This memory can be accessed by the accessor
  * functions provided by this code. During the boot process, it checks whether
  * allocation of huge chunk of memory is needed or not. If not, it avoids
  * allocating memory at all. With this advantage, we can include this feature
  * into the kernel in default and can avoid rebuild and solve related problems.
  *
  * To help these things to work well, there are two callbacks for clients. One
  * is the need callback which is mandatory if user wants to avoid useless
  * memory allocation at boot-time. The other is optional, init callback, which
  * is used to do proper initialization after memory is allocated.
  *
  * The need callback is used to decide whether extended memory allocation is
  * needed or not. Sometimes users want to deactivate some features in this
  * boot and extra memory would be unneccessary. In this case, to avoid
  * allocating huge chunk of memory, each clients represent their need of
  * extra memory through the need callback. If one of the need callbacks
  * returns true, it means that someone needs extra memory so that
  * page extension core should allocates memory for page extension. If
  * none of need callbacks return true, memory isn't needed at all in this boot
  * and page extension core can skip to allocate memory. As result,
  * none of memory is wasted.
  *
  * When need callback returns true, page_ext checks if there is a request for
  * extra memory through size in struct page_ext_operations. If it is non-zero,
  * extra space is allocated for each page_ext entry and offset is returned to
  * user through offset in struct page_ext_operations.
  *
  * The init callback is used to do proper initialization after page extension
  * is completely initialized. In sparse memory system, extra memory is
  * allocated some time later than memmap is allocated. In other words, lifetime
  * of memory for page extension isn't same with memmap for struct page.
  * Therefore, clients can't store extra data until page extension is
  * initialized, even if pages are allocated and used freely. This could
  * cause inadequate state of extra data per page, so, to prevent it, client
  * can utilize this callback to initialize the state of it correctly.
  */

 static struct page_ext_operations *page_ext_ops[] = {
 #ifdef CONFIG_PAGE_OWNER
 	&page_owner_ops,
 #endif
 #if defined(CONFIG_IDLE_PAGE_TRACKING) && !defined(CONFIG_64BIT)
 	&page_idle_ops,
 #endif
 };

 unsigned long page_ext_size = sizeof(struct page_ext);

 static unsigned long total_usage;

 static bool __init invoke_need_callbacks(void)
 {
 	int i;
 	int entries = ARRAY_SIZE(page_ext_ops);
 	bool need = false;

 	for (i = 0; i < entries; i++) {
 		if (page_ext_ops[i]->need && page_ext_ops[i]->need()) {
 			page_ext_ops[i]->offset = page_ext_size;
 			page_ext_size += page_ext_ops[i]->size;
 			need = true;
 		}
 	}

 	return need;
 }

 static void __init invoke_init_callbacks(void)
 {
 	int i;
 	int entries = ARRAY_SIZE(page_ext_ops);

 	for (i = 0; i < entries; i++) {
 		if (page_ext_ops[i]->init)
 			page_ext_ops[i]->init();
 	}
 }

 static inline struct page_ext *get_entry(void *base, unsigned long index)
 {
 	return base + page_ext_size * index;
 }

 #if !defined(CONFIG_SPARSEMEM)


 void __meminit pgdat_page_ext_init(struct pglist_data *pgdat)
 {
 	pgdat->node_page_ext = NULL;
 }

 struct page_ext *lookup_page_ext(const struct page *page)
 {
 	unsigned long pfn = page_to_pfn(page);
 	unsigned long index;
 	struct page_ext *base;

 	base = NODE_DATA(page_to_nid(page))->node_page_ext;
 	/*
 	 * The sanity checks the page allocator does upon freeing a
 	 * page can reach here before the page_ext arrays are
 	 * allocated when feeding a range of pages to the allocator
 	 * for the first time during bootup or memory hotplug.
 	 */
 	if (unlikely(!base))
 		return NULL;
 	index = pfn - round_down(node_start_pfn(page_to_nid(page)),
 					MAX_ORDER_NR_PAGES);
 	return get_entry(base, index);
 }

 static int __init alloc_node_page_ext(int nid)
 {
 	struct page_ext *base;
 	unsigned long table_size;
 	unsigned long nr_pages;

 	nr_pages = NODE_DATA(nid)->node_spanned_pages;
 	if (!nr_pages)
 		return 0;

 	/*
 	 * Need extra space if node range is not aligned with
 	 * MAX_ORDER_NR_PAGES. When page allocator's buddy algorithm
 	 * checks buddy's status, range could be out of exact node range.
 	 */
 	if (!IS_ALIGNED(node_start_pfn(nid), MAX_ORDER_NR_PAGES) ||
 		!IS_ALIGNED(node_end_pfn(nid), MAX_ORDER_NR_PAGES))
 		nr_pages += MAX_ORDER_NR_PAGES;

 	table_size = page_ext_size * nr_pages;

 	base = memblock_alloc_try_nid(
 			table_size, PAGE_SIZE, __pa(MAX_DMA_ADDRESS),
 			MEMBLOCK_ALLOC_ACCESSIBLE, nid);
 	if (!base)
 		return -ENOMEM;
 	NODE_DATA(nid)->node_page_ext = base;
 	total_usage += table_size;
 	return 0;
 }

 void __init page_ext_init_flatmem(void)
 {

 	int nid, fail;

 	if (!invoke_need_callbacks())
 		return;

 	for_each_online_node(nid)  {
 		fail = alloc_node_page_ext(nid);
 		if (fail)
 			goto fail;
 	}
 	pr_info("allocated %ld bytes of page_ext\n", total_usage);
 	invoke_init_callbacks();
 	return;

 fail:
 	pr_crit("allocation of page_ext failed.\n");
 	panic("Out of memory");
 }

 #else /* CONFIG_FLAT_NODE_MEM_MAP */

 struct page_ext *lookup_page_ext(const struct page *page)
 {
 	unsigned long pfn = page_to_pfn(page);
 	struct mem_section *section = __pfn_to_section(pfn);
 	/*
 	 * The sanity checks the page allocator does upon freeing a
 	 * page can reach here before the page_ext arrays are
 	 * allocated when feeding a range of pages to the allocator
 	 * for the first time during bootup or memory hotplug.
 	 */
 	if (!section->page_ext)
 		return NULL;
 	return get_entry(section->page_ext, pfn);
 }

 static void *__meminit alloc_page_ext(size_t size, int nid)
 {
 	gfp_t flags = GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN;
 	void *addr = NULL;

 	addr = alloc_pages_exact_nid(nid, size, flags);
 	if (addr) {
 		kmemleak_alloc(addr, size, 1, flags);
 		return addr;
 	}

 	addr = vzalloc_node(size, nid);

 	return addr;
 }

 static int __meminit init_section_page_ext(unsigned long pfn, int nid)
 {
 	struct mem_section *section;
 	struct page_ext *base;
 	unsigned long table_size;

 	section = __pfn_to_section(pfn);

 	if (section->page_ext)
 		return 0;

 	table_size = page_ext_size * PAGES_PER_SECTION;
 	base = alloc_page_ext(table_size, nid);

 	/*
 	 * The value stored in section->page_ext is (base - pfn)
 	 * and it does not point to the memory block allocated above,
 	 * causing kmemleak false positives.
 	 */
 	kmemleak_not_leak(base);

 	if (!base) {
 		pr_err("page ext allocation failure\n");
 		return -ENOMEM;
 	}

 	/*
 	 * The passed "pfn" may not be aligned to SECTION.  For the calculation
 	 * we need to apply a mask.
 	 */
 	pfn &= PAGE_SECTION_MASK;
 	section->page_ext = (void *)base - page_ext_size * pfn;
 	total_usage += table_size;
 	return 0;
 }
 #ifdef CONFIG_MEMORY_HOTPLUG
 static void free_page_ext(void *addr)
 {
 	if (is_vmalloc_addr(addr)) {
 		vfree(addr);
 	} else {
 		struct page *page = virt_to_page(addr);
 		size_t table_size;

 		table_size = page_ext_size * PAGES_PER_SECTION;

 		BUG_ON(PageReserved(page));
 		kmemleak_free(addr);
 		free_pages_exact(addr, table_size);
 	}
 }

 static void __free_page_ext(unsigned long pfn)
 {
 	struct mem_section *ms;
 	struct page_ext *base;

 	ms = __pfn_to_section(pfn);
 	if (!ms || !ms->page_ext)
 		return;
 	base = get_entry(ms->page_ext, pfn);
 	free_page_ext(base);
 	ms->page_ext = NULL;
 }

 static int __meminit online_page_ext(unsigned long start_pfn,
 				unsigned long nr_pages,
 				int nid)
 {
 	unsigned long start, end, pfn;
 	int fail = 0;

 	start = SECTION_ALIGN_DOWN(start_pfn);
 	end = SECTION_ALIGN_UP(start_pfn + nr_pages);

 	if (nid == NUMA_NO_NODE) {
 		/*
 		 * In this case, "nid" already exists and contains valid memory.
 		 * "start_pfn" passed to us is a pfn which is an arg for
 		 * online__pages(), and start_pfn should exist.
 		 */
 		nid = pfn_to_nid(start_pfn);
 		VM_BUG_ON(!node_state(nid, N_ONLINE));
 	}

 	for (pfn = start; !fail && pfn < end; pfn += PAGES_PER_SECTION) {
 		if (!pfn_present(pfn))
 			continue;
 		fail = init_section_page_ext(pfn, nid);
 	}
 	if (!fail)
 		return 0;

 	/* rollback */
 	for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION)
 		__free_page_ext(pfn);

 	return -ENOMEM;
 }

 static int __meminit offline_page_ext(unsigned long start_pfn,
 				unsigned long nr_pages, int nid)
 {
 	unsigned long start, end, pfn;

 	start = SECTION_ALIGN_DOWN(start_pfn);
 	end = SECTION_ALIGN_UP(start_pfn + nr_pages);

 	for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION)
 		__free_page_ext(pfn);
 	return 0;

 }

 static int __meminit page_ext_callback(struct notifier_block *self,
 			       unsigned long action, void *arg)
 {
 	struct memory_notify *mn = arg;
 	int ret = 0;

 	switch (action) {
 	case MEM_GOING_ONLINE:
 		ret = online_page_ext(mn->start_pfn,
 				   mn->nr_pages, mn->status_change_nid);
 		break;
 	case MEM_OFFLINE:
 		offline_page_ext(mn->start_pfn,
 				mn->nr_pages, mn->status_change_nid);
 		break;
 	case MEM_CANCEL_ONLINE:
 		offline_page_ext(mn->start_pfn,
 				mn->nr_pages, mn->status_change_nid);
 		break;
 	case MEM_GOING_OFFLINE:
 		break;
 	case MEM_ONLINE:
 	case MEM_CANCEL_OFFLINE:
 		break;
 	}

 	return notifier_from_errno(ret);
 }

 #endif

 void __init page_ext_init(void)
 {
 	unsigned long pfn;
 	int nid;

 	if (!invoke_need_callbacks())
 		return;

 	for_each_node_state(nid, N_MEMORY) {
 		unsigned long start_pfn, end_pfn;

 		start_pfn = node_start_pfn(nid);
 		end_pfn = node_end_pfn(nid);
 		/*
 		 * start_pfn and end_pfn may not be aligned to SECTION and the
 		 * page->flags of out of node pages are not initialized.  So we
 		 * scan [start_pfn, the biggest section's pfn < end_pfn) here.
 		 */
 		for (pfn = start_pfn; pfn < end_pfn;
 			pfn = ALIGN(pfn + 1, PAGES_PER_SECTION)) {

 			if (!pfn_valid(pfn))
 				continue;
 			/*
 			 * Nodes's pfns can be overlapping.
 			 * We know some arch can have a nodes layout such as
 			 * -------------pfn-------------->
 			 * N0 | N1 | N2 | N0 | N1 | N2|....
 			 */
 			if (pfn_to_nid(pfn) != nid)
 				continue;
 			if (init_section_page_ext(pfn, nid))
 				goto oom;
 			cond_resched();
 		}
 	}
 	hotplug_memory_notifier(page_ext_callback, 0);
 	pr_info("allocated %ld bytes of page_ext\n", total_usage);
 	invoke_init_callbacks();
 	return;

 oom:
 	panic("Out of memory");
 }

 void __meminit pgdat_page_ext_init(struct pglist_data *pgdat)
 {
 }

 #endif
	// SPDX-License-Identifier: GPL-2.0
	#include <linux/mm.h>
	#include <linux/mmzone.h>
	#include <linux/memblock.h>
	#include <linux/page_ext.h>
	#include <linux/memory.h>
	#include <linux/vmalloc.h>
	#include <linux/kmemleak.h>
	#include <linux/page_owner.h>
	#include <linux/page_idle.h>

	/*
	* struct page extension
	*
	* This is the feature to manage memory for extended data per page.
	*
	* Until now, we must modify struct page itself to store extra data per page.
	* This requires rebuilding the kernel and it is really time consuming process.
	* And, sometimes, rebuild is impossible due to third party module dependency.
	* At last, enlarging struct page could cause un-wanted system behaviour change.
	*
	* This feature is intended to overcome above mentioned problems. This feature
	* allocates memory for extended data per page in certain place rather than
	* the struct page itself. This memory can be accessed by the accessor
	* functions provided by this code. During the boot process, it checks whether
	* allocation of huge chunk of memory is needed or not. If not, it avoids
	* allocating memory at all. With this advantage, we can include this feature
	* into the kernel in default and can avoid rebuild and solve related problems.
	*
	* To help these things to work well, there are two callbacks for clients. One
	* is the need callback which is mandatory if user wants to avoid useless
	* memory allocation at boot-time. The other is optional, init callback, which
	* is used to do proper initialization after memory is allocated.
	*
	* The need callback is used to decide whether extended memory allocation is
	* needed or not. Sometimes users want to deactivate some features in this
	* boot and extra memory would be unneccessary. In this case, to avoid
	* allocating huge chunk of memory, each clients represent their need of
	* extra memory through the need callback. If one of the need callbacks
	* returns true, it means that someone needs extra memory so that
	* page extension core should allocates memory for page extension. If
	* none of need callbacks return true, memory isn't needed at all in this boot
	* and page extension core can skip to allocate memory. As result,
	* none of memory is wasted.
	*
	* When need callback returns true, page_ext checks if there is a request for
	* extra memory through size in struct page_ext_operations. If it is non-zero,
	* extra space is allocated for each page_ext entry and offset is returned to
	* user through offset in struct page_ext_operations.
	*
	* The init callback is used to do proper initialization after page extension
	* is completely initialized. In sparse memory system, extra memory is
	* allocated some time later than memmap is allocated. In other words, lifetime
	* of memory for page extension isn't same with memmap for struct page.
	* Therefore, clients can't store extra data until page extension is
	* initialized, even if pages are allocated and used freely. This could
	* cause inadequate state of extra data per page, so, to prevent it, client
	* can utilize this callback to initialize the state of it correctly.
	*/

	static struct page_ext_operations *page_ext_ops[] = {
	#ifdef CONFIG_PAGE_OWNER
	&page_owner_ops,
	#endif
	#if defined(CONFIG_IDLE_PAGE_TRACKING) && !defined(CONFIG_64BIT)
	&page_idle_ops,
	#endif
	};

	unsigned long page_ext_size = sizeof(struct page_ext);

	static unsigned long total_usage;

	static bool __init invoke_need_callbacks(void)
	{
	int i;
	int entries = ARRAY_SIZE(page_ext_ops);
	bool need = false;

	for (i = 0; i < entries; i++) {
	if (page_ext_ops[i]->need && page_ext_ops[i]->need()) {
	page_ext_ops[i]->offset = page_ext_size;
	page_ext_size += page_ext_ops[i]->size;
	need = true;
	}
	}

	return need;
	}

	static void __init invoke_init_callbacks(void)
	{
	int i;
	int entries = ARRAY_SIZE(page_ext_ops);

	for (i = 0; i < entries; i++) {
	if (page_ext_ops[i]->init)
	page_ext_ops[i]->init();
	}
	}

	static inline struct page_ext get_entry(void base, unsigned long index)
	{
	return base + page_ext_size * index;
	}

	#if !defined(CONFIG_SPARSEMEM)


	void __meminit pgdat_page_ext_init(struct pglist_data *pgdat)
	{
	pgdat->node_page_ext = NULL;
	}

	struct page_ext lookup_page_ext(const struct page page)
	{
	unsigned long pfn = page_to_pfn(page);
	unsigned long index;
	struct page_ext *base;

	base = NODE_DATA(page_to_nid(page))->node_page_ext;
	/*
	* The sanity checks the page allocator does upon freeing a
	* page can reach here before the page_ext arrays are
	* allocated when feeding a range of pages to the allocator
	* for the first time during bootup or memory hotplug.
	*/
	if (unlikely(!base))
	return NULL;
	index = pfn - round_down(node_start_pfn(page_to_nid(page)),
	MAX_ORDER_NR_PAGES);
	return get_entry(base, index);
	}

	static int __init alloc_node_page_ext(int nid)
	{
	struct page_ext *base;
	unsigned long table_size;
	unsigned long nr_pages;

	nr_pages = NODE_DATA(nid)->node_spanned_pages;
	if (!nr_pages)
	return 0;

	/*
	* Need extra space if node range is not aligned with
	* MAX_ORDER_NR_PAGES. When page allocator's buddy algorithm
	* checks buddy's status, range could be out of exact node range.
	*/
	if (!IS_ALIGNED(node_start_pfn(nid), MAX_ORDER_NR_PAGES) \|\|
	!IS_ALIGNED(node_end_pfn(nid), MAX_ORDER_NR_PAGES))
	nr_pages += MAX_ORDER_NR_PAGES;

	table_size = page_ext_size * nr_pages;

	base = memblock_alloc_try_nid(
	table_size, PAGE_SIZE, __pa(MAX_DMA_ADDRESS),
	MEMBLOCK_ALLOC_ACCESSIBLE, nid);
	if (!base)
	return -ENOMEM;
	NODE_DATA(nid)->node_page_ext = base;
	total_usage += table_size;
	return 0;
	}

	void __init page_ext_init_flatmem(void)
	{

	int nid, fail;

	if (!invoke_need_callbacks())
	return;

	for_each_online_node(nid) {
	fail = alloc_node_page_ext(nid);
	if (fail)
	goto fail;
	}
	pr_info("allocated %ld bytes of page_ext\n", total_usage);
	invoke_init_callbacks();
	return;

	fail:
	pr_crit("allocation of page_ext failed.\n");
	panic("Out of memory");
	}

	#else /* CONFIG_FLAT_NODE_MEM_MAP */

	struct page_ext lookup_page_ext(const struct page page)
	{
	unsigned long pfn = page_to_pfn(page);
	struct mem_section *section = __pfn_to_section(pfn);
	/*
	* The sanity checks the page allocator does upon freeing a
	* page can reach here before the page_ext arrays are
	* allocated when feeding a range of pages to the allocator
	* for the first time during bootup or memory hotplug.
	*/
	if (!section->page_ext)
	return NULL;
	return get_entry(section->page_ext, pfn);
	}

	static void *__meminit alloc_page_ext(size_t size, int nid)
	{
	gfp_t flags = GFP_KERNEL \| __GFP_ZERO \| __GFP_NOWARN;
	void *addr = NULL;

	addr = alloc_pages_exact_nid(nid, size, flags);
	if (addr) {
	kmemleak_alloc(addr, size, 1, flags);
	return addr;
	}

	addr = vzalloc_node(size, nid);

	return addr;
	}

	static int __meminit init_section_page_ext(unsigned long pfn, int nid)
	{
	struct mem_section *section;
	struct page_ext *base;
	unsigned long table_size;

	section = __pfn_to_section(pfn);

	if (section->page_ext)
	return 0;

	table_size = page_ext_size * PAGES_PER_SECTION;
	base = alloc_page_ext(table_size, nid);

	/*
	* The value stored in section->page_ext is (base - pfn)
	* and it does not point to the memory block allocated above,
	* causing kmemleak false positives.
	*/
	kmemleak_not_leak(base);

	if (!base) {
	pr_err("page ext allocation failure\n");
	return -ENOMEM;
	}

	/*
	* The passed "pfn" may not be aligned to SECTION. For the calculation
	* we need to apply a mask.
	*/
	pfn &= PAGE_SECTION_MASK;
	section->page_ext = (void )base - page_ext_size pfn;
	total_usage += table_size;
	return 0;
	}
	#ifdef CONFIG_MEMORY_HOTPLUG
	static void free_page_ext(void *addr)
	{
	if (is_vmalloc_addr(addr)) {
	vfree(addr);
	} else {
	struct page *page = virt_to_page(addr);
	size_t table_size;

	table_size = page_ext_size * PAGES_PER_SECTION;

	BUG_ON(PageReserved(page));
	kmemleak_free(addr);
	free_pages_exact(addr, table_size);
	}
	}

	static void __free_page_ext(unsigned long pfn)
	{
	struct mem_section *ms;
	struct page_ext *base;

	ms = __pfn_to_section(pfn);
	if (!ms \|\| !ms->page_ext)
	return;
	base = get_entry(ms->page_ext, pfn);
	free_page_ext(base);
	ms->page_ext = NULL;
	}

	static int __meminit online_page_ext(unsigned long start_pfn,
	unsigned long nr_pages,
	int nid)
	{
	unsigned long start, end, pfn;
	int fail = 0;

	start = SECTION_ALIGN_DOWN(start_pfn);
	end = SECTION_ALIGN_UP(start_pfn + nr_pages);

	if (nid == NUMA_NO_NODE) {
	/*
	* In this case, "nid" already exists and contains valid memory.
	* "start_pfn" passed to us is a pfn which is an arg for
	* online__pages(), and start_pfn should exist.
	*/
	nid = pfn_to_nid(start_pfn);
	VM_BUG_ON(!node_state(nid, N_ONLINE));
	}

	for (pfn = start; !fail && pfn < end; pfn += PAGES_PER_SECTION) {
	if (!pfn_present(pfn))
	continue;
	fail = init_section_page_ext(pfn, nid);
	}
	if (!fail)
	return 0;

	/* rollback */
	for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION)
	__free_page_ext(pfn);

	return -ENOMEM;
	}

	static int __meminit offline_page_ext(unsigned long start_pfn,
	unsigned long nr_pages, int nid)
	{
	unsigned long start, end, pfn;

	start = SECTION_ALIGN_DOWN(start_pfn);
	end = SECTION_ALIGN_UP(start_pfn + nr_pages);

	for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION)
	__free_page_ext(pfn);
	return 0;

	}

	static int __meminit page_ext_callback(struct notifier_block *self,
	unsigned long action, void *arg)
	{
	struct memory_notify *mn = arg;
	int ret = 0;

	switch (action) {
	case MEM_GOING_ONLINE:
	ret = online_page_ext(mn->start_pfn,
	mn->nr_pages, mn->status_change_nid);
	break;
	case MEM_OFFLINE:
	offline_page_ext(mn->start_pfn,
	mn->nr_pages, mn->status_change_nid);
	break;
	case MEM_CANCEL_ONLINE:
	offline_page_ext(mn->start_pfn,
	mn->nr_pages, mn->status_change_nid);
	break;
	case MEM_GOING_OFFLINE:
	break;
	case MEM_ONLINE:
	case MEM_CANCEL_OFFLINE:
	break;
	}

	return notifier_from_errno(ret);
	}

	#endif

	void __init page_ext_init(void)
	{
	unsigned long pfn;
	int nid;

	if (!invoke_need_callbacks())
	return;

	for_each_node_state(nid, N_MEMORY) {
	unsigned long start_pfn, end_pfn;

	start_pfn = node_start_pfn(nid);
	end_pfn = node_end_pfn(nid);
	/*
	* start_pfn and end_pfn may not be aligned to SECTION and the
	* page->flags of out of node pages are not initialized. So we
	* scan [start_pfn, the biggest section's pfn < end_pfn) here.
	*/
	for (pfn = start_pfn; pfn < end_pfn;
	pfn = ALIGN(pfn + 1, PAGES_PER_SECTION)) {

	if (!pfn_valid(pfn))
	continue;
	/*
	* Nodes's pfns can be overlapping.
	* We know some arch can have a nodes layout such as
	* -------------pfn-------------->
	* N0 \| N1 \| N2 \| N0 \| N1 \| N2\|....
	*/
	if (pfn_to_nid(pfn) != nid)
	continue;
	if (init_section_page_ext(pfn, nid))
	goto oom;
	cond_resched();
	}
	}
	hotplug_memory_notifier(page_ext_callback, 0);
	pr_info("allocated %ld bytes of page_ext\n", total_usage);
	invoke_init_callbacks();
	return;

	oom:
	panic("Out of memory");
	}

	void __meminit pgdat_page_ext_init(struct pglist_data *pgdat)
	{
	}

	#endif