text: #include <linux/mm.h>
  #include <linux/mmzone.h>
  #include <linux/bootmem.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.
   *
   * 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[] = {
  	&debug_guardpage_ops,
  #ifdef CONFIG_PAGE_POISONING
  	&page_poisoning_ops,
  #endif
  #ifdef CONFIG_PAGE_OWNER
  	&page_owner_ops,
  #endif
  #if defined(CONFIG_IDLE_PAGE_TRACKING) && !defined(CONFIG_64BIT)
  	&page_idle_ops,
  #endif
  };
  
  static unsigned long total_usage;
  
  static bool __init invoke_need_callbacks(void)
  {
  	int i;
  	int entries = ARRAY_SIZE(page_ext_ops);
  
  	for (i = 0; i < entries; i++) {
  		if (page_ext_ops[i]->need && page_ext_ops[i]->need())
  			return true;
  	}
  
  	return false;
  }
  
  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();
  	}
  }
  
  #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(struct page *page)
  {
  	unsigned long pfn = page_to_pfn(page);
  	unsigned long offset;
  	struct page_ext *base;
  
  	base = NODE_DATA(page_to_nid(page))->node_page_ext;
  #if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
  	/*
  	 * 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.
  	 *
  	 * This check is also necessary for ensuring page poisoning
  	 * works as expected when enabled
  	 */
  	if (unlikely(!base))
  		return NULL;
  #endif
  	offset = pfn - round_down(node_start_pfn(page_to_nid(page)),
  					MAX_ORDER_NR_PAGES);
  	return base + offset;
  }
  
  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 = sizeof(struct page_ext) * nr_pages;
  
  	base = memblock_virt_alloc_try_nid_nopanic(
  			table_size, PAGE_SIZE, __pa(MAX_DMA_ADDRESS),
  			BOOTMEM_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(struct page *page)
  {
  	unsigned long pfn = page_to_pfn(page);
  	struct mem_section *section = __pfn_to_section(pfn);
  #if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
  	/*
  	 * 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.
  	 *
  	 * This check is also necessary for ensuring page poisoning
  	 * works as expected when enabled
  	 */
  	if (!section->page_ext)
  		return NULL;
  #endif
  	return 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;
  	}
  
  	if (node_state(nid, N_HIGH_MEMORY))
  		addr = vzalloc_node(size, nid);
  	else
  		addr = vzalloc(size);
  
  	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 = sizeof(struct page_ext) * 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 = base - 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 = sizeof(struct page_ext) * PAGES_PER_SECTION;
  
  		BUG_ON(PageReserved(page));
  		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 = 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 == -1) {
  		/*
  		 * 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|....
  			 *
  			 * Take into account DEFERRED_STRUCT_PAGE_INIT.
  			 */
  			if (early_pfn_to_nid(pfn) != nid)
  				continue;
  			if (init_section_page_ext(pfn, nid))
  				goto oom;
  		}
  	}
  	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
  