/*
   *  Copyright (C) 2009  Red Hat, Inc.
   *
   *  This work is licensed under the terms of the GNU GPL, version 2. See
   *  the COPYING file in the top-level directory.
   */
  
  #include <linux/mm.h>
  #include <linux/sched.h>
  #include <linux/highmem.h>
  #include <linux/hugetlb.h>
  #include <linux/mmu_notifier.h>
  #include <linux/rmap.h>
  #include <linux/swap.h>

  #include <linux/mm_inline.h>
  #include <linux/kthread.h>
  #include <linux/khugepaged.h>

  #include <linux/freezer.h>

  #include <linux/mman.h>

  #include <asm/tlb.h>
  #include <asm/pgalloc.h>
  #include "internal.h"

  /*
   * By default transparent hugepage support is enabled for all mappings
   * and khugepaged scans all mappings. Defrag is only invoked by
   * khugepaged hugepage allocations and by page faults inside
   * MADV_HUGEPAGE regions to avoid the risk of slowing down short lived
   * allocations.
   */

  unsigned long transparent_hugepage_flags __read_mostly =

  #ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS

  	(1<<TRANSPARENT_HUGEPAGE_FLAG)|

  #endif
  #ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE
  	(1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)|
  #endif

  	(1<<TRANSPARENT_HUGEPAGE_DEFRAG_FLAG)|

  	(1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
  
  /* default scan 8*512 pte (or vmas) every 30 second */
  static unsigned int khugepaged_pages_to_scan __read_mostly = HPAGE_PMD_NR*8;
  static unsigned int khugepaged_pages_collapsed;
  static unsigned int khugepaged_full_scans;
  static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
  /* during fragmentation poll the hugepage allocator once every minute */
  static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
  static struct task_struct *khugepaged_thread __read_mostly;
  static DEFINE_MUTEX(khugepaged_mutex);
  static DEFINE_SPINLOCK(khugepaged_mm_lock);
  static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
  /*
   * default collapse hugepages if there is at least one pte mapped like
   * it would have happened if the vma was large enough during page
   * fault.
   */
  static unsigned int khugepaged_max_ptes_none __read_mostly = HPAGE_PMD_NR-1;
  
  static int khugepaged(void *none);
  static int mm_slots_hash_init(void);
  static int khugepaged_slab_init(void);
  static void khugepaged_slab_free(void);
  
  #define MM_SLOTS_HASH_HEADS 1024
  static struct hlist_head *mm_slots_hash __read_mostly;
  static struct kmem_cache *mm_slot_cache __read_mostly;
  
  /**
   * struct mm_slot - hash lookup from mm to mm_slot
   * @hash: hash collision list
   * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
   * @mm: the mm that this information is valid for
   */
  struct mm_slot {
  	struct hlist_node hash;
  	struct list_head mm_node;
  	struct mm_struct *mm;
  };
  
  /**
   * struct khugepaged_scan - cursor for scanning
   * @mm_head: the head of the mm list to scan
   * @mm_slot: the current mm_slot we are scanning
   * @address: the next address inside that to be scanned
   *
   * There is only the one khugepaged_scan instance of this cursor structure.
   */
  struct khugepaged_scan {
  	struct list_head mm_head;
  	struct mm_slot *mm_slot;
  	unsigned long address;

  };
  static struct khugepaged_scan khugepaged_scan = {

  	.mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
  };

  
  static int set_recommended_min_free_kbytes(void)
  {
  	struct zone *zone;
  	int nr_zones = 0;
  	unsigned long recommended_min;
  	extern int min_free_kbytes;
  
  	if (!test_bit(TRANSPARENT_HUGEPAGE_FLAG,
  		      &transparent_hugepage_flags) &&
  	    !test_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
  		      &transparent_hugepage_flags))
  		return 0;
  
  	for_each_populated_zone(zone)
  		nr_zones++;
  
  	/* Make sure at least 2 hugepages are free for MIGRATE_RESERVE */
  	recommended_min = pageblock_nr_pages * nr_zones * 2;
  
  	/*
  	 * Make sure that on average at least two pageblocks are almost free
  	 * of another type, one for a migratetype to fall back to and a
  	 * second to avoid subsequent fallbacks of other types There are 3
  	 * MIGRATE_TYPES we care about.
  	 */
  	recommended_min += pageblock_nr_pages * nr_zones *
  			   MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
  
  	/* don't ever allow to reserve more than 5% of the lowmem */
  	recommended_min = min(recommended_min,
  			      (unsigned long) nr_free_buffer_pages() / 20);
  	recommended_min <<= (PAGE_SHIFT-10);
  
  	if (recommended_min > min_free_kbytes)
  		min_free_kbytes = recommended_min;
  	setup_per_zone_wmarks();
  	return 0;
  }
  late_initcall(set_recommended_min_free_kbytes);

  static int start_khugepaged(void)
  {
  	int err = 0;
  	if (khugepaged_enabled()) {
  		int wakeup;
  		if (unlikely(!mm_slot_cache || !mm_slots_hash)) {
  			err = -ENOMEM;
  			goto out;
  		}
  		mutex_lock(&khugepaged_mutex);
  		if (!khugepaged_thread)
  			khugepaged_thread = kthread_run(khugepaged, NULL,
  							"khugepaged");
  		if (unlikely(IS_ERR(khugepaged_thread))) {
  			printk(KERN_ERR
  			       "khugepaged: kthread_run(khugepaged) failed
  ");
  			err = PTR_ERR(khugepaged_thread);
  			khugepaged_thread = NULL;
  		}
  		wakeup = !list_empty(&khugepaged_scan.mm_head);
  		mutex_unlock(&khugepaged_mutex);
  		if (wakeup)
  			wake_up_interruptible(&khugepaged_wait);

  
  		set_recommended_min_free_kbytes();

  	} else
  		/* wakeup to exit */
  		wake_up_interruptible(&khugepaged_wait);
  out:
  	return err;
  }

  
  #ifdef CONFIG_SYSFS

  static ssize_t double_flag_show(struct kobject *kobj,
  				struct kobj_attribute *attr, char *buf,
  				enum transparent_hugepage_flag enabled,
  				enum transparent_hugepage_flag req_madv)
  {
  	if (test_bit(enabled, &transparent_hugepage_flags)) {
  		VM_BUG_ON(test_bit(req_madv, &transparent_hugepage_flags));
  		return sprintf(buf, "[always] madvise never
  ");
  	} else if (test_bit(req_madv, &transparent_hugepage_flags))
  		return sprintf(buf, "always [madvise] never
  ");
  	else
  		return sprintf(buf, "always madvise [never]
  ");
  }
  static ssize_t double_flag_store(struct kobject *kobj,
  				 struct kobj_attribute *attr,
  				 const char *buf, size_t count,
  				 enum transparent_hugepage_flag enabled,
  				 enum transparent_hugepage_flag req_madv)
  {
  	if (!memcmp("always", buf,
  		    min(sizeof("always")-1, count))) {
  		set_bit(enabled, &transparent_hugepage_flags);
  		clear_bit(req_madv, &transparent_hugepage_flags);
  	} else if (!memcmp("madvise", buf,
  			   min(sizeof("madvise")-1, count))) {
  		clear_bit(enabled, &transparent_hugepage_flags);
  		set_bit(req_madv, &transparent_hugepage_flags);
  	} else if (!memcmp("never", buf,
  			   min(sizeof("never")-1, count))) {
  		clear_bit(enabled, &transparent_hugepage_flags);
  		clear_bit(req_madv, &transparent_hugepage_flags);
  	} else
  		return -EINVAL;
  
  	return count;
  }
  
  static ssize_t enabled_show(struct kobject *kobj,
  			    struct kobj_attribute *attr, char *buf)
  {
  	return double_flag_show(kobj, attr, buf,
  				TRANSPARENT_HUGEPAGE_FLAG,
  				TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
  }
  static ssize_t enabled_store(struct kobject *kobj,
  			     struct kobj_attribute *attr,
  			     const char *buf, size_t count)
  {

  	ssize_t ret;
  
  	ret = double_flag_store(kobj, attr, buf, count,
  				TRANSPARENT_HUGEPAGE_FLAG,
  				TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
  
  	if (ret > 0) {
  		int err = start_khugepaged();
  		if (err)
  			ret = err;
  	}

  	if (ret > 0 &&
  	    (test_bit(TRANSPARENT_HUGEPAGE_FLAG,
  		      &transparent_hugepage_flags) ||
  	     test_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
  		      &transparent_hugepage_flags)))
  		set_recommended_min_free_kbytes();

  	return ret;

  }
  static struct kobj_attribute enabled_attr =
  	__ATTR(enabled, 0644, enabled_show, enabled_store);
  
  static ssize_t single_flag_show(struct kobject *kobj,
  				struct kobj_attribute *attr, char *buf,
  				enum transparent_hugepage_flag flag)
  {

  	return sprintf(buf, "%d
  ",
  		       !!test_bit(flag, &transparent_hugepage_flags));

  }

  static ssize_t single_flag_store(struct kobject *kobj,
  				 struct kobj_attribute *attr,
  				 const char *buf, size_t count,
  				 enum transparent_hugepage_flag flag)
  {

  	unsigned long value;
  	int ret;
  
  	ret = kstrtoul(buf, 10, &value);
  	if (ret < 0)
  		return ret;
  	if (value > 1)
  		return -EINVAL;
  
  	if (value)

  		set_bit(flag, &transparent_hugepage_flags);

  	else

  		clear_bit(flag, &transparent_hugepage_flags);

  
  	return count;
  }
  
  /*
   * Currently defrag only disables __GFP_NOWAIT for allocation. A blind
   * __GFP_REPEAT is too aggressive, it's never worth swapping tons of
   * memory just to allocate one more hugepage.
   */
  static ssize_t defrag_show(struct kobject *kobj,
  			   struct kobj_attribute *attr, char *buf)
  {
  	return double_flag_show(kobj, attr, buf,
  				TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
  				TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
  }
  static ssize_t defrag_store(struct kobject *kobj,
  			    struct kobj_attribute *attr,
  			    const char *buf, size_t count)
  {
  	return double_flag_store(kobj, attr, buf, count,
  				 TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
  				 TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
  }
  static struct kobj_attribute defrag_attr =
  	__ATTR(defrag, 0644, defrag_show, defrag_store);
  
  #ifdef CONFIG_DEBUG_VM
  static ssize_t debug_cow_show(struct kobject *kobj,
  				struct kobj_attribute *attr, char *buf)
  {
  	return single_flag_show(kobj, attr, buf,
  				TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
  }
  static ssize_t debug_cow_store(struct kobject *kobj,
  			       struct kobj_attribute *attr,
  			       const char *buf, size_t count)
  {
  	return single_flag_store(kobj, attr, buf, count,
  				 TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
  }
  static struct kobj_attribute debug_cow_attr =
  	__ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store);
  #endif /* CONFIG_DEBUG_VM */
  
  static struct attribute *hugepage_attr[] = {
  	&enabled_attr.attr,
  	&defrag_attr.attr,
  #ifdef CONFIG_DEBUG_VM
  	&debug_cow_attr.attr,
  #endif
  	NULL,
  };
  
  static struct attribute_group hugepage_attr_group = {
  	.attrs = hugepage_attr,

  };
  
  static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
  					 struct kobj_attribute *attr,
  					 char *buf)
  {
  	return sprintf(buf, "%u
  ", khugepaged_scan_sleep_millisecs);
  }
  
  static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
  					  struct kobj_attribute *attr,
  					  const char *buf, size_t count)
  {
  	unsigned long msecs;
  	int err;
  
  	err = strict_strtoul(buf, 10, &msecs);
  	if (err || msecs > UINT_MAX)
  		return -EINVAL;
  
  	khugepaged_scan_sleep_millisecs = msecs;
  	wake_up_interruptible(&khugepaged_wait);
  
  	return count;
  }
  static struct kobj_attribute scan_sleep_millisecs_attr =
  	__ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
  	       scan_sleep_millisecs_store);
  
  static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
  					  struct kobj_attribute *attr,
  					  char *buf)
  {
  	return sprintf(buf, "%u
  ", khugepaged_alloc_sleep_millisecs);
  }
  
  static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
  					   struct kobj_attribute *attr,
  					   const char *buf, size_t count)
  {
  	unsigned long msecs;
  	int err;
  
  	err = strict_strtoul(buf, 10, &msecs);
  	if (err || msecs > UINT_MAX)
  		return -EINVAL;
  
  	khugepaged_alloc_sleep_millisecs = msecs;
  	wake_up_interruptible(&khugepaged_wait);
  
  	return count;
  }
  static struct kobj_attribute alloc_sleep_millisecs_attr =
  	__ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
  	       alloc_sleep_millisecs_store);
  
  static ssize_t pages_to_scan_show(struct kobject *kobj,
  				  struct kobj_attribute *attr,
  				  char *buf)
  {
  	return sprintf(buf, "%u
  ", khugepaged_pages_to_scan);
  }
  static ssize_t pages_to_scan_store(struct kobject *kobj,
  				   struct kobj_attribute *attr,
  				   const char *buf, size_t count)
  {
  	int err;
  	unsigned long pages;
  
  	err = strict_strtoul(buf, 10, &pages);
  	if (err || !pages || pages > UINT_MAX)
  		return -EINVAL;
  
  	khugepaged_pages_to_scan = pages;
  
  	return count;
  }
  static struct kobj_attribute pages_to_scan_attr =
  	__ATTR(pages_to_scan, 0644, pages_to_scan_show,
  	       pages_to_scan_store);
  
  static ssize_t pages_collapsed_show(struct kobject *kobj,
  				    struct kobj_attribute *attr,
  				    char *buf)
  {
  	return sprintf(buf, "%u
  ", khugepaged_pages_collapsed);
  }
  static struct kobj_attribute pages_collapsed_attr =
  	__ATTR_RO(pages_collapsed);
  
  static ssize_t full_scans_show(struct kobject *kobj,
  			       struct kobj_attribute *attr,
  			       char *buf)
  {
  	return sprintf(buf, "%u
  ", khugepaged_full_scans);
  }
  static struct kobj_attribute full_scans_attr =
  	__ATTR_RO(full_scans);
  
  static ssize_t khugepaged_defrag_show(struct kobject *kobj,
  				      struct kobj_attribute *attr, char *buf)
  {
  	return single_flag_show(kobj, attr, buf,
  				TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
  }
  static ssize_t khugepaged_defrag_store(struct kobject *kobj,
  				       struct kobj_attribute *attr,
  				       const char *buf, size_t count)
  {
  	return single_flag_store(kobj, attr, buf, count,
  				 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
  }
  static struct kobj_attribute khugepaged_defrag_attr =
  	__ATTR(defrag, 0644, khugepaged_defrag_show,
  	       khugepaged_defrag_store);
  
  /*
   * max_ptes_none controls if khugepaged should collapse hugepages over
   * any unmapped ptes in turn potentially increasing the memory
   * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
   * reduce the available free memory in the system as it
   * runs. Increasing max_ptes_none will instead potentially reduce the
   * free memory in the system during the khugepaged scan.
   */
  static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
  					     struct kobj_attribute *attr,
  					     char *buf)
  {
  	return sprintf(buf, "%u
  ", khugepaged_max_ptes_none);
  }
  static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
  					      struct kobj_attribute *attr,
  					      const char *buf, size_t count)
  {
  	int err;
  	unsigned long max_ptes_none;
  
  	err = strict_strtoul(buf, 10, &max_ptes_none);
  	if (err || max_ptes_none > HPAGE_PMD_NR-1)
  		return -EINVAL;
  
  	khugepaged_max_ptes_none = max_ptes_none;
  
  	return count;
  }
  static struct kobj_attribute khugepaged_max_ptes_none_attr =
  	__ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
  	       khugepaged_max_ptes_none_store);
  
  static struct attribute *khugepaged_attr[] = {
  	&khugepaged_defrag_attr.attr,
  	&khugepaged_max_ptes_none_attr.attr,
  	&pages_to_scan_attr.attr,
  	&pages_collapsed_attr.attr,
  	&full_scans_attr.attr,
  	&scan_sleep_millisecs_attr.attr,
  	&alloc_sleep_millisecs_attr.attr,
  	NULL,
  };
  
  static struct attribute_group khugepaged_attr_group = {
  	.attrs = khugepaged_attr,
  	.name = "khugepaged",

  };

  static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)

  {

  	int err;

  	*hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
  	if (unlikely(!*hugepage_kobj)) {

  		printk(KERN_ERR "hugepage: failed kobject create
  ");

  		return -ENOMEM;

  	}

  	err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);

  	if (err) {
  		printk(KERN_ERR "hugepage: failed register hugeage group
  ");

  		goto delete_obj;

  	}

  	err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);

  	if (err) {
  		printk(KERN_ERR "hugepage: failed register hugeage group
  ");

  		goto remove_hp_group;

  	}

  
  	return 0;
  
  remove_hp_group:
  	sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
  delete_obj:
  	kobject_put(*hugepage_kobj);
  	return err;
  }
  
  static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
  {
  	sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
  	sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
  	kobject_put(hugepage_kobj);
  }
  #else
  static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
  {
  	return 0;
  }
  
  static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
  {
  }
  #endif /* CONFIG_SYSFS */
  
  static int __init hugepage_init(void)
  {
  	int err;
  	struct kobject *hugepage_kobj;
  
  	if (!has_transparent_hugepage()) {
  		transparent_hugepage_flags = 0;
  		return -EINVAL;
  	}
  
  	err = hugepage_init_sysfs(&hugepage_kobj);
  	if (err)
  		return err;

  
  	err = khugepaged_slab_init();
  	if (err)
  		goto out;
  
  	err = mm_slots_hash_init();
  	if (err) {
  		khugepaged_slab_free();
  		goto out;
  	}

  	/*
  	 * By default disable transparent hugepages on smaller systems,
  	 * where the extra memory used could hurt more than TLB overhead
  	 * is likely to save.  The admin can still enable it through /sys.
  	 */
  	if (totalram_pages < (512 << (20 - PAGE_SHIFT)))
  		transparent_hugepage_flags = 0;

  	start_khugepaged();

  	set_recommended_min_free_kbytes();

  	return 0;

  out:

  	hugepage_exit_sysfs(hugepage_kobj);

  	return err;

  }
  module_init(hugepage_init)
  
  static int __init setup_transparent_hugepage(char *str)
  {
  	int ret = 0;
  	if (!str)
  		goto out;
  	if (!strcmp(str, "always")) {
  		set_bit(TRANSPARENT_HUGEPAGE_FLAG,
  			&transparent_hugepage_flags);
  		clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
  			  &transparent_hugepage_flags);
  		ret = 1;
  	} else if (!strcmp(str, "madvise")) {
  		clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
  			  &transparent_hugepage_flags);
  		set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
  			&transparent_hugepage_flags);
  		ret = 1;
  	} else if (!strcmp(str, "never")) {
  		clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
  			  &transparent_hugepage_flags);
  		clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
  			  &transparent_hugepage_flags);
  		ret = 1;
  	}
  out:
  	if (!ret)
  		printk(KERN_WARNING
  		       "transparent_hugepage= cannot parse, ignored
  ");
  	return ret;
  }
  __setup("transparent_hugepage=", setup_transparent_hugepage);
  
  static void prepare_pmd_huge_pte(pgtable_t pgtable,
  				 struct mm_struct *mm)
  {
  	assert_spin_locked(&mm->page_table_lock);
  
  	/* FIFO */
  	if (!mm->pmd_huge_pte)
  		INIT_LIST_HEAD(&pgtable->lru);
  	else
  		list_add(&pgtable->lru, &mm->pmd_huge_pte->lru);
  	mm->pmd_huge_pte = pgtable;
  }
  
  static inline pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
  {
  	if (likely(vma->vm_flags & VM_WRITE))
  		pmd = pmd_mkwrite(pmd);
  	return pmd;
  }
  
  static int __do_huge_pmd_anonymous_page(struct mm_struct *mm,
  					struct vm_area_struct *vma,
  					unsigned long haddr, pmd_t *pmd,
  					struct page *page)
  {
  	int ret = 0;
  	pgtable_t pgtable;
  
  	VM_BUG_ON(!PageCompound(page));
  	pgtable = pte_alloc_one(mm, haddr);
  	if (unlikely(!pgtable)) {

  		mem_cgroup_uncharge_page(page);

  		put_page(page);
  		return VM_FAULT_OOM;
  	}
  
  	clear_huge_page(page, haddr, HPAGE_PMD_NR);
  	__SetPageUptodate(page);
  
  	spin_lock(&mm->page_table_lock);
  	if (unlikely(!pmd_none(*pmd))) {
  		spin_unlock(&mm->page_table_lock);

  		mem_cgroup_uncharge_page(page);

  		put_page(page);
  		pte_free(mm, pgtable);
  	} else {
  		pmd_t entry;
  		entry = mk_pmd(page, vma->vm_page_prot);
  		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
  		entry = pmd_mkhuge(entry);
  		/*
  		 * The spinlocking to take the lru_lock inside
  		 * page_add_new_anon_rmap() acts as a full memory
  		 * barrier to be sure clear_huge_page writes become
  		 * visible after the set_pmd_at() write.
  		 */
  		page_add_new_anon_rmap(page, vma, haddr);
  		set_pmd_at(mm, haddr, pmd, entry);
  		prepare_pmd_huge_pte(pgtable, mm);
  		add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
  		spin_unlock(&mm->page_table_lock);
  	}
  
  	return ret;
  }

  static inline gfp_t alloc_hugepage_gfpmask(int defrag, gfp_t extra_gfp)

  {

  	return (GFP_TRANSHUGE & ~(defrag ? 0 : __GFP_WAIT)) | extra_gfp;

  }
  
  static inline struct page *alloc_hugepage_vma(int defrag,
  					      struct vm_area_struct *vma,

  					      unsigned long haddr, int nd,
  					      gfp_t extra_gfp)

  {

  	return alloc_pages_vma(alloc_hugepage_gfpmask(defrag, extra_gfp),

  			       HPAGE_PMD_ORDER, vma, haddr, nd);

  }
  
  #ifndef CONFIG_NUMA

  static inline struct page *alloc_hugepage(int defrag)
  {

  	return alloc_pages(alloc_hugepage_gfpmask(defrag, 0),

  			   HPAGE_PMD_ORDER);
  }

  #endif

  
  int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
  			       unsigned long address, pmd_t *pmd,
  			       unsigned int flags)
  {
  	struct page *page;
  	unsigned long haddr = address & HPAGE_PMD_MASK;
  	pte_t *pte;
  
  	if (haddr >= vma->vm_start && haddr + HPAGE_PMD_SIZE <= vma->vm_end) {
  		if (unlikely(anon_vma_prepare(vma)))
  			return VM_FAULT_OOM;

  		if (unlikely(khugepaged_enter(vma)))
  			return VM_FAULT_OOM;

  		page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),

  					  vma, haddr, numa_node_id(), 0);

  		if (unlikely(!page)) {
  			count_vm_event(THP_FAULT_FALLBACK);

  			goto out;

  		}
  		count_vm_event(THP_FAULT_ALLOC);

  		if (unlikely(mem_cgroup_newpage_charge(page, mm, GFP_KERNEL))) {
  			put_page(page);
  			goto out;
  		}

  
  		return __do_huge_pmd_anonymous_page(mm, vma, haddr, pmd, page);
  	}
  out:
  	/*
  	 * Use __pte_alloc instead of pte_alloc_map, because we can't
  	 * run pte_offset_map on the pmd, if an huge pmd could
  	 * materialize from under us from a different thread.
  	 */
  	if (unlikely(__pte_alloc(mm, vma, pmd, address)))
  		return VM_FAULT_OOM;
  	/* if an huge pmd materialized from under us just retry later */
  	if (unlikely(pmd_trans_huge(*pmd)))
  		return 0;
  	/*
  	 * A regular pmd is established and it can't morph into a huge pmd
  	 * from under us anymore at this point because we hold the mmap_sem
  	 * read mode and khugepaged takes it in write mode. So now it's
  	 * safe to run pte_offset_map().
  	 */
  	pte = pte_offset_map(pmd, address);
  	return handle_pte_fault(mm, vma, address, pte, pmd, flags);
  }
  
  int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
  		  pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
  		  struct vm_area_struct *vma)
  {
  	struct page *src_page;
  	pmd_t pmd;
  	pgtable_t pgtable;
  	int ret;
  
  	ret = -ENOMEM;
  	pgtable = pte_alloc_one(dst_mm, addr);
  	if (unlikely(!pgtable))
  		goto out;
  
  	spin_lock(&dst_mm->page_table_lock);
  	spin_lock_nested(&src_mm->page_table_lock, SINGLE_DEPTH_NESTING);
  
  	ret = -EAGAIN;
  	pmd = *src_pmd;
  	if (unlikely(!pmd_trans_huge(pmd))) {
  		pte_free(dst_mm, pgtable);
  		goto out_unlock;
  	}
  	if (unlikely(pmd_trans_splitting(pmd))) {
  		/* split huge page running from under us */
  		spin_unlock(&src_mm->page_table_lock);
  		spin_unlock(&dst_mm->page_table_lock);
  		pte_free(dst_mm, pgtable);
  
  		wait_split_huge_page(vma->anon_vma, src_pmd); /* src_vma */
  		goto out;
  	}
  	src_page = pmd_page(pmd);
  	VM_BUG_ON(!PageHead(src_page));
  	get_page(src_page);
  	page_dup_rmap(src_page);
  	add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
  
  	pmdp_set_wrprotect(src_mm, addr, src_pmd);
  	pmd = pmd_mkold(pmd_wrprotect(pmd));
  	set_pmd_at(dst_mm, addr, dst_pmd, pmd);
  	prepare_pmd_huge_pte(pgtable, dst_mm);
  
  	ret = 0;
  out_unlock:
  	spin_unlock(&src_mm->page_table_lock);
  	spin_unlock(&dst_mm->page_table_lock);
  out:
  	return ret;
  }
  
  /* no "address" argument so destroys page coloring of some arch */
  pgtable_t get_pmd_huge_pte(struct mm_struct *mm)
  {
  	pgtable_t pgtable;
  
  	assert_spin_locked(&mm->page_table_lock);
  
  	/* FIFO */
  	pgtable = mm->pmd_huge_pte;
  	if (list_empty(&pgtable->lru))
  		mm->pmd_huge_pte = NULL;
  	else {
  		mm->pmd_huge_pte = list_entry(pgtable->lru.next,
  					      struct page, lru);
  		list_del(&pgtable->lru);
  	}
  	return pgtable;
  }
  
  static int do_huge_pmd_wp_page_fallback(struct mm_struct *mm,
  					struct vm_area_struct *vma,
  					unsigned long address,
  					pmd_t *pmd, pmd_t orig_pmd,
  					struct page *page,
  					unsigned long haddr)
  {
  	pgtable_t pgtable;
  	pmd_t _pmd;
  	int ret = 0, i;
  	struct page **pages;
  
  	pages = kmalloc(sizeof(struct page *) * HPAGE_PMD_NR,
  			GFP_KERNEL);
  	if (unlikely(!pages)) {
  		ret |= VM_FAULT_OOM;
  		goto out;
  	}
  
  	for (i = 0; i < HPAGE_PMD_NR; i++) {

  		pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE |
  					       __GFP_OTHER_NODE,

  					       vma, address, page_to_nid(page));

  		if (unlikely(!pages[i] ||
  			     mem_cgroup_newpage_charge(pages[i], mm,
  						       GFP_KERNEL))) {
  			if (pages[i])

  				put_page(pages[i]);

  			mem_cgroup_uncharge_start();
  			while (--i >= 0) {
  				mem_cgroup_uncharge_page(pages[i]);
  				put_page(pages[i]);
  			}
  			mem_cgroup_uncharge_end();

  			kfree(pages);
  			ret |= VM_FAULT_OOM;
  			goto out;
  		}
  	}
  
  	for (i = 0; i < HPAGE_PMD_NR; i++) {
  		copy_user_highpage(pages[i], page + i,

  				   haddr + PAGE_SIZE * i, vma);

  		__SetPageUptodate(pages[i]);
  		cond_resched();
  	}
  
  	spin_lock(&mm->page_table_lock);
  	if (unlikely(!pmd_same(*pmd, orig_pmd)))
  		goto out_free_pages;
  	VM_BUG_ON(!PageHead(page));
  
  	pmdp_clear_flush_notify(vma, haddr, pmd);
  	/* leave pmd empty until pte is filled */
  
  	pgtable = get_pmd_huge_pte(mm);
  	pmd_populate(mm, &_pmd, pgtable);
  
  	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
  		pte_t *pte, entry;
  		entry = mk_pte(pages[i], vma->vm_page_prot);
  		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
  		page_add_new_anon_rmap(pages[i], vma, haddr);
  		pte = pte_offset_map(&_pmd, haddr);
  		VM_BUG_ON(!pte_none(*pte));
  		set_pte_at(mm, haddr, pte, entry);
  		pte_unmap(pte);
  	}
  	kfree(pages);
  
  	mm->nr_ptes++;
  	smp_wmb(); /* make pte visible before pmd */
  	pmd_populate(mm, pmd, pgtable);
  	page_remove_rmap(page);
  	spin_unlock(&mm->page_table_lock);
  
  	ret |= VM_FAULT_WRITE;
  	put_page(page);
  
  out:
  	return ret;
  
  out_free_pages:
  	spin_unlock(&mm->page_table_lock);

  	mem_cgroup_uncharge_start();
  	for (i = 0; i < HPAGE_PMD_NR; i++) {
  		mem_cgroup_uncharge_page(pages[i]);

  		put_page(pages[i]);

  	}
  	mem_cgroup_uncharge_end();

  	kfree(pages);
  	goto out;
  }
  
  int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
  			unsigned long address, pmd_t *pmd, pmd_t orig_pmd)
  {
  	int ret = 0;
  	struct page *page, *new_page;
  	unsigned long haddr;
  
  	VM_BUG_ON(!vma->anon_vma);
  	spin_lock(&mm->page_table_lock);
  	if (unlikely(!pmd_same(*pmd, orig_pmd)))
  		goto out_unlock;
  
  	page = pmd_page(orig_pmd);
  	VM_BUG_ON(!PageCompound(page) || !PageHead(page));
  	haddr = address & HPAGE_PMD_MASK;
  	if (page_mapcount(page) == 1) {
  		pmd_t entry;
  		entry = pmd_mkyoung(orig_pmd);
  		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
  		if (pmdp_set_access_flags(vma, haddr, pmd, entry,  1))
  			update_mmu_cache(vma, address, entry);
  		ret |= VM_FAULT_WRITE;
  		goto out_unlock;
  	}
  	get_page(page);
  	spin_unlock(&mm->page_table_lock);
  
  	if (transparent_hugepage_enabled(vma) &&
  	    !transparent_hugepage_debug_cow())

  		new_page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),

  					      vma, haddr, numa_node_id(), 0);

  	else
  		new_page = NULL;
  
  	if (unlikely(!new_page)) {

  		count_vm_event(THP_FAULT_FALLBACK);

  		ret = do_huge_pmd_wp_page_fallback(mm, vma, address,
  						   pmd, orig_pmd, page, haddr);
  		put_page(page);
  		goto out;
  	}

  	count_vm_event(THP_FAULT_ALLOC);

  	if (unlikely(mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL))) {
  		put_page(new_page);
  		put_page(page);
  		ret |= VM_FAULT_OOM;
  		goto out;
  	}

  	copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
  	__SetPageUptodate(new_page);
  
  	spin_lock(&mm->page_table_lock);
  	put_page(page);

  	if (unlikely(!pmd_same(*pmd, orig_pmd))) {
  		mem_cgroup_uncharge_page(new_page);

  		put_page(new_page);

  	} else {

  		pmd_t entry;
  		VM_BUG_ON(!PageHead(page));
  		entry = mk_pmd(new_page, vma->vm_page_prot);
  		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
  		entry = pmd_mkhuge(entry);
  		pmdp_clear_flush_notify(vma, haddr, pmd);
  		page_add_new_anon_rmap(new_page, vma, haddr);
  		set_pmd_at(mm, haddr, pmd, entry);
  		update_mmu_cache(vma, address, entry);
  		page_remove_rmap(page);
  		put_page(page);
  		ret |= VM_FAULT_WRITE;
  	}
  out_unlock:
  	spin_unlock(&mm->page_table_lock);
  out:
  	return ret;
  }
  
  struct page *follow_trans_huge_pmd(struct mm_struct *mm,
  				   unsigned long addr,
  				   pmd_t *pmd,
  				   unsigned int flags)
  {
  	struct page *page = NULL;
  
  	assert_spin_locked(&mm->page_table_lock);
  
  	if (flags & FOLL_WRITE && !pmd_write(*pmd))
  		goto out;
  
  	page = pmd_page(*pmd);
  	VM_BUG_ON(!PageHead(page));
  	if (flags & FOLL_TOUCH) {
  		pmd_t _pmd;
  		/*
  		 * We should set the dirty bit only for FOLL_WRITE but
  		 * for now the dirty bit in the pmd is meaningless.
  		 * And if the dirty bit will become meaningful and
  		 * we'll only set it with FOLL_WRITE, an atomic
  		 * set_bit will be required on the pmd to set the
  		 * young bit, instead of the current set_pmd_at.
  		 */
  		_pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
  		set_pmd_at(mm, addr & HPAGE_PMD_MASK, pmd, _pmd);
  	}
  	page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
  	VM_BUG_ON(!PageCompound(page));
  	if (flags & FOLL_GET)

  		get_page_foll(page);

  
  out:
  	return page;
  }
  
  int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,

  		 pmd_t *pmd, unsigned long addr)

  {
  	int ret = 0;
  
  	spin_lock(&tlb->mm->page_table_lock);
  	if (likely(pmd_trans_huge(*pmd))) {
  		if (unlikely(pmd_trans_splitting(*pmd))) {
  			spin_unlock(&tlb->mm->page_table_lock);
  			wait_split_huge_page(vma->anon_vma,
  					     pmd);
  		} else {
  			struct page *page;
  			pgtable_t pgtable;
  			pgtable = get_pmd_huge_pte(tlb->mm);
  			page = pmd_page(*pmd);
  			pmd_clear(pmd);

  			tlb_remove_pmd_tlb_entry(tlb, pmd, addr);

  			page_remove_rmap(page);
  			VM_BUG_ON(page_mapcount(page) < 0);
  			add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
  			VM_BUG_ON(!PageHead(page));
  			spin_unlock(&tlb->mm->page_table_lock);
  			tlb_remove_page(tlb, page);
  			pte_free(tlb->mm, pgtable);
  			ret = 1;
  		}
  	} else
  		spin_unlock(&tlb->mm->page_table_lock);
  
  	return ret;
  }

  int mincore_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
  		unsigned long addr, unsigned long end,
  		unsigned char *vec)
  {
  	int ret = 0;
  
  	spin_lock(&vma->vm_mm->page_table_lock);
  	if (likely(pmd_trans_huge(*pmd))) {
  		ret = !pmd_trans_splitting(*pmd);
  		spin_unlock(&vma->vm_mm->page_table_lock);
  		if (unlikely(!ret))
  			wait_split_huge_page(vma->anon_vma, pmd);
  		else {
  			/*
  			 * All logical pages in the range are present
  			 * if backed by a huge page.
  			 */
  			memset(vec, 1, (end - addr) >> PAGE_SHIFT);
  		}
  	} else
  		spin_unlock(&vma->vm_mm->page_table_lock);
  
  	return ret;
  }

  int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
  		  unsigned long old_addr,
  		  unsigned long new_addr, unsigned long old_end,
  		  pmd_t *old_pmd, pmd_t *new_pmd)
  {
  	int ret = 0;
  	pmd_t pmd;
  
  	struct mm_struct *mm = vma->vm_mm;
  
  	if ((old_addr & ~HPAGE_PMD_MASK) ||
  	    (new_addr & ~HPAGE_PMD_MASK) ||
  	    old_end - old_addr < HPAGE_PMD_SIZE ||
  	    (new_vma->vm_flags & VM_NOHUGEPAGE))
  		goto out;
  
  	/*
  	 * The destination pmd shouldn't be established, free_pgtables()
  	 * should have release it.
  	 */
  	if (WARN_ON(!pmd_none(*new_pmd))) {
  		VM_BUG_ON(pmd_trans_huge(*new_pmd));
  		goto out;
  	}
  
  	spin_lock(&mm->page_table_lock);
  	if (likely(pmd_trans_huge(*old_pmd))) {
  		if (pmd_trans_splitting(*old_pmd)) {
  			spin_unlock(&mm->page_table_lock);
  			wait_split_huge_page(vma->anon_vma, old_pmd);
  			ret = -1;
  		} else {
  			pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
  			VM_BUG_ON(!pmd_none(*new_pmd));
  			set_pmd_at(mm, new_addr, new_pmd, pmd);
  			spin_unlock(&mm->page_table_lock);
  			ret = 1;
  		}
  	} else {
  		spin_unlock(&mm->page_table_lock);
  	}
  out:
  	return ret;
  }

  int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
  		unsigned long addr, pgprot_t newprot)
  {
  	struct mm_struct *mm = vma->vm_mm;
  	int ret = 0;
  
  	spin_lock(&mm->page_table_lock);
  	if (likely(pmd_trans_huge(*pmd))) {
  		if (unlikely(pmd_trans_splitting(*pmd))) {
  			spin_unlock(&mm->page_table_lock);
  			wait_split_huge_page(vma->anon_vma, pmd);
  		} else {
  			pmd_t entry;
  
  			entry = pmdp_get_and_clear(mm, addr, pmd);
  			entry = pmd_modify(entry, newprot);
  			set_pmd_at(mm, addr, pmd, entry);
  			spin_unlock(&vma->vm_mm->page_table_lock);

  			ret = 1;
  		}
  	} else
  		spin_unlock(&vma->vm_mm->page_table_lock);
  
  	return ret;
  }

  pmd_t *page_check_address_pmd(struct page *page,
  			      struct mm_struct *mm,
  			      unsigned long address,
  			      enum page_check_address_pmd_flag flag)
  {
  	pgd_t *pgd;
  	pud_t *pud;
  	pmd_t *pmd, *ret = NULL;
  
  	if (address & ~HPAGE_PMD_MASK)
  		goto out;
  
  	pgd = pgd_offset(mm, address);
  	if (!pgd_present(*pgd))
  		goto out;
  
  	pud = pud_offset(pgd, address);
  	if (!pud_present(*pud))
  		goto out;
  
  	pmd = pmd_offset(pud, address);
  	if (pmd_none(*pmd))
  		goto out;
  	if (pmd_page(*pmd) != page)
  		goto out;

  	/*
  	 * split_vma() may create temporary aliased mappings. There is
  	 * no risk as long as all huge pmd are found and have their
  	 * splitting bit set before __split_huge_page_refcount
  	 * runs. Finding the same huge pmd more than once during the
  	 * same rmap walk is not a problem.
  	 */
  	if (flag == PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG &&
  	    pmd_trans_splitting(*pmd))
  		goto out;

  	if (pmd_trans_huge(*pmd)) {
  		VM_BUG_ON(flag == PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG &&
  			  !pmd_trans_splitting(*pmd));
  		ret = pmd;
  	}
  out:
  	return ret;
  }
  
  static int __split_huge_page_splitting(struct page *page,
  				       struct vm_area_struct *vma,
  				       unsigned long address)
  {
  	struct mm_struct *mm = vma->vm_mm;
  	pmd_t *pmd;
  	int ret = 0;
  
  	spin_lock(&mm->page_table_lock);
  	pmd = page_check_address_pmd(page, mm, address,
  				     PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG);
  	if (pmd) {
  		/*
  		 * We can't temporarily set the pmd to null in order
  		 * to split it, the pmd must remain marked huge at all
  		 * times or the VM won't take the pmd_trans_huge paths

  		 * and it won't wait on the anon_vma->root->mutex to

  		 * serialize against split_huge_page*.
  		 */
  		pmdp_splitting_flush_notify(vma, address, pmd);
  		ret = 1;
  	}
  	spin_unlock(&mm->page_table_lock);
  
  	return ret;
  }
  
  static void __split_huge_page_refcount(struct page *page)
  {
  	int i;

  	struct zone *zone = page_zone(page);

  	int tail_count = 0;

  
  	/* prevent PageLRU to go away from under us, and freeze lru stats */
  	spin_lock_irq(&zone->lru_lock);
  	compound_lock(page);

  	/* complete memcg works before add pages to LRU */
  	mem_cgroup_split_huge_fixup(page);

  	for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {

  		struct page *page_tail = page + i;

  		/* tail_page->_mapcount cannot change */
  		BUG_ON(page_mapcount(page_tail) < 0);
  		tail_count += page_mapcount(page_tail);
  		/* check for overflow */
  		BUG_ON(tail_count < 0);
  		BUG_ON(atomic_read(&page_tail->_count) != 0);
  		/*
  		 * tail_page->_count is zero and not changing from
  		 * under us. But get_page_unless_zero() may be running
  		 * from under us on the tail_page. If we used
  		 * atomic_set() below instead of atomic_add(), we
  		 * would then run atomic_set() concurrently with
  		 * get_page_unless_zero(), and atomic_set() is
  		 * implemented in C not using locked ops. spin_unlock
  		 * on x86 sometime uses locked ops because of PPro
  		 * errata 66, 92, so unless somebody can guarantee
  		 * atomic_set() here would be safe on all archs (and
  		 * not only on x86), it's safer to use atomic_add().
  		 */
  		atomic_add(page_mapcount(page) + page_mapcount(page_tail) + 1,
  			   &page_tail->_count);

  
  		/* after clearing PageTail the gup refcount can be released */
  		smp_mb();

  		/*
  		 * retain hwpoison flag of the poisoned tail page:
  		 *   fix for the unsuitable process killed on Guest Machine(KVM)
  		 *   by the memory-failure.
  		 */
  		page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP | __PG_HWPOISON;

  		page_tail->flags |= (page->flags &
  				     ((1L << PG_referenced) |
  				      (1L << PG_swapbacked) |
  				      (1L << PG_mlocked) |
  				      (1L << PG_uptodate)));
  		page_tail->flags |= (1L << PG_dirty);

  		/* clear PageTail before overwriting first_page */

  		smp_wmb();
  
  		/*
  		 * __split_huge_page_splitting() already set the
  		 * splitting bit in all pmd that could map this
  		 * hugepage, that will ensure no CPU can alter the
  		 * mapcount on the head page. The mapcount is only
  		 * accounted in the head page and it has to be
  		 * transferred to all tail pages in the below code. So
  		 * for this code to be safe, the split the mapcount
  		 * can't change. But that doesn't mean userland can't
  		 * keep changing and reading the page contents while
  		 * we transfer the mapcount, so the pmd splitting
  		 * status is achieved setting a reserved bit in the
  		 * pmd, not by clearing the present bit.
  		*/

  		page_tail->_mapcount = page->_mapcount;
  
  		BUG_ON(page_tail->mapping);
  		page_tail->mapping = page->mapping;

  		page_tail->index = page->index + i;

  
  		BUG_ON(!PageAnon(page_tail));
  		BUG_ON(!PageUptodate(page_tail));
  		BUG_ON(!PageDirty(page_tail));
  		BUG_ON(!PageSwapBacked(page_tail));

  		lru_add_page_tail(zone, page, page_tail);
  	}

  	atomic_sub(tail_count, &page->_count);
  	BUG_ON(atomic_read(&page->_count) <= 0);

  	__dec_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES);
  	__mod_zone_page_state(zone, NR_ANON_PAGES, HPAGE_PMD_NR);

  	ClearPageCompound(page);
  	compound_unlock(page);
  	spin_unlock_irq(&zone->lru_lock);
  
  	for (i = 1; i < HPAGE_PMD_NR; i++) {
  		struct page *page_tail = page + i;
  		BUG_ON(page_count(page_tail) <= 0);
  		/*
  		 * Tail pages may be freed if there wasn't any mapping
  		 * like if add_to_swap() is running on a lru page that
  		 * had its mapping zapped. And freeing these pages
  		 * requires taking the lru_lock so we do the put_page
  		 * of the tail pages after the split is complete.
  		 */
  		put_page(page_tail);
  	}
  
  	/*
  	 * Only the head page (now become a regular page) is required
  	 * to be pinned by the caller.
  	 */
  	BUG_ON(page_count(page) <= 0);
  }
  
  static int __split_huge_page_map(struct page *page,
  				 struct vm_area_struct *vma,
  				 unsigned long address)
  {
  	struct mm_struct *mm = vma->vm_mm;
  	pmd_t *pmd, _pmd;
  	int ret = 0, i;
  	pgtable_t pgtable;
  	unsigned long haddr;
  
  	spin_lock(&mm->page_table_lock);
  	pmd = page_check_address_pmd(page, mm, address,
  				     PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG);
  	if (pmd) {
  		pgtable = get_pmd_huge_pte(mm);
  		pmd_populate(mm, &_pmd, pgtable);
  
  		for (i = 0, haddr = address; i < HPAGE_PMD_NR;
  		     i++, haddr += PAGE_SIZE) {
  			pte_t *pte, entry;
  			BUG_ON(PageCompound(page+i));
  			entry = mk_pte(page + i, vma->vm_page_prot);
  			entry = maybe_mkwrite(pte_mkdirty(entry), vma);
  			if (!pmd_write(*pmd))
  				entry = pte_wrprotect(entry);
  			else
  				BUG_ON(page_mapcount(page) != 1);
  			if (!pmd_young(*pmd))
  				entry = pte_mkold(entry);
  			pte = pte_offset_map(&_pmd, haddr);
  			BUG_ON(!pte_none(*pte));
  			set_pte_at(mm, haddr, pte, entry);
  			pte_unmap(pte);
  		}
  
  		mm->nr_ptes++;
  		smp_wmb(); /* make pte visible before pmd */
  		/*
  		 * Up to this point the pmd is present and huge and
  		 * userland has the whole access to the hugepage
  		 * during the split (which happens in place). If we
  		 * overwrite the pmd with the not-huge version
  		 * pointing to the pte here (which of course we could
  		 * if all CPUs were bug free), userland could trigger
  		 * a small page size TLB miss on the small sized TLB
  		 * while the hugepage TLB entry is still established
  		 * in the huge TLB. Some CPU doesn't like that. See
  		 * http://support.amd.com/us/Processor_TechDocs/41322.pdf,
  		 * Erratum 383 on page 93. Intel should be safe but is
  		 * also warns that it's only safe if the permission
  		 * and cache attributes of the two entries loaded in
  		 * the two TLB is identical (which should be the case
  		 * here). But it is generally safer to never allow
  		 * small and huge TLB entries for the same virtual
  		 * address to be loaded simultaneously. So instead of
  		 * doing "pmd_populate(); flush_tlb_range();" we first
  		 * mark the current pmd notpresent (atomically because
  		 * here the pmd_trans_huge and pmd_trans_splitting
  		 * must remain set at all times on the pmd until the
  		 * split is complete for this pmd), then we flush the
  		 * SMP TLB and finally we write the non-huge version
  		 * of the pmd entry with pmd_populate.
  		 */
  		set_pmd_at(mm, address, pmd, pmd_mknotpresent(*pmd));
  		flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
  		pmd_populate(mm, pmd, pgtable);
  		ret = 1;
  	}
  	spin_unlock(&mm->page_table_lock);
  
  	return ret;
  }

  /* must be called with anon_vma->root->mutex hold */

  static void __split_huge_page(struct page *page,
  			      struct anon_vma *anon_vma)
  {
  	int mapcount, mapcount2;
  	struct anon_vma_chain *avc;
  
  	BUG_ON(!PageHead(page));
  	BUG_ON(PageTail(page));
  
  	mapcount = 0;
  	list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
  		struct vm_area_struct *vma = avc->vma;
  		unsigned long addr = vma_address(page, vma);
  		BUG_ON(is_vma_temporary_stack(vma));
  		if (addr == -EFAULT)
  			continue;
  		mapcount += __split_huge_page_splitting(page, vma, addr);
  	}

  	/*
  	 * It is critical that new vmas are added to the tail of the
  	 * anon_vma list. This guarantes that if copy_huge_pmd() runs
  	 * and establishes a child pmd before
  	 * __split_huge_page_splitting() freezes the parent pmd (so if
  	 * we fail to prevent copy_huge_pmd() from running until the
  	 * whole __split_huge_page() is complete), we will still see
  	 * the newly established pmd of the child later during the
  	 * walk, to be able to set it as pmd_trans_splitting too.
  	 */
  	if (mapcount != page_mapcount(page))
  		printk(KERN_ERR "mapcount %d page_mapcount %d
  ",
  		       mapcount, page_mapcount(page));

  	BUG_ON(mapcount != page_mapcount(page));
  
  	__split_huge_page_refcount(page);
  
  	mapcount2 = 0;
  	list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
  		struct vm_area_struct *vma = avc->vma;
  		unsigned long addr = vma_address(page, vma);
  		BUG_ON(is_vma_temporary_stack(vma));
  		if (addr == -EFAULT)
  			continue;
  		mapcount2 += __split_huge_page_map(page, vma, addr);
  	}

  	if (mapcount != mapcount2)
  		printk(KERN_ERR "mapcount %d mapcount2 %d page_mapcount %d
  ",
  		       mapcount, mapcount2, page_mapcount(page));

  	BUG_ON(mapcount != mapcount2);
  }
  
  int split_huge_page(struct page *page)
  {
  	struct anon_vma *anon_vma;
  	int ret = 1;
  
  	BUG_ON(!PageAnon(page));
  	anon_vma = page_lock_anon_vma(page);
  	if (!anon_vma)
  		goto out;
  	ret = 0;
  	if (!PageCompound(page))
  		goto out_unlock;
  
  	BUG_ON(!PageSwapBacked(page));
  	__split_huge_page(page, anon_vma);

  	count_vm_event(THP_SPLIT);

  
  	BUG_ON(PageCompound(page));
  out_unlock:
  	page_unlock_anon_vma(anon_vma);
  out:
  	return ret;
  }

  #define VM_NO_THP (VM_SPECIAL|VM_INSERTPAGE|VM_MIXEDMAP|VM_SAO| \
  		   VM_HUGETLB|VM_SHARED|VM_MAYSHARE)

  int hugepage_madvise(struct vm_area_struct *vma,
  		     unsigned long *vm_flags, int advice)

  {

  	switch (advice) {
  	case MADV_HUGEPAGE:
  		/*
  		 * Be somewhat over-protective like KSM for now!
  		 */

  		if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP))

  			return -EINVAL;
  		*vm_flags &= ~VM_NOHUGEPAGE;
  		*vm_flags |= VM_HUGEPAGE;

  		/*
  		 * If the vma become good for khugepaged to scan,
  		 * register it here without waiting a page fault that
  		 * may not happen any time soon.
  		 */
  		if (unlikely(khugepaged_enter_vma_merge(vma)))
  			return -ENOMEM;

  		break;
  	case MADV_NOHUGEPAGE:
  		/*
  		 * Be somewhat over-protective like KSM for now!
  		 */

  		if (*vm_flags & (VM_NOHUGEPAGE | VM_NO_THP))

  			return -EINVAL;
  		*vm_flags &= ~VM_HUGEPAGE;
  		*vm_flags |= VM_NOHUGEPAGE;

  		/*
  		 * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
  		 * this vma even if we leave the mm registered in khugepaged if
  		 * it got registered before VM_NOHUGEPAGE was set.
  		 */

  		break;
  	}

  
  	return 0;
  }

  static int __init khugepaged_slab_init(void)
  {
  	mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
  					  sizeof(struct mm_slot),
  					  __alignof__(struct mm_slot), 0, NULL);
  	if (!mm_slot_cache)
  		return -ENOMEM;
  
  	return 0;
  }
  
  static void __init khugepaged_slab_free(void)
  {
  	kmem_cache_destroy(mm_slot_cache);
  	mm_slot_cache = NULL;
  }
  
  static inline struct mm_slot *alloc_mm_slot(void)
  {
  	if (!mm_slot_cache)	/* initialization failed */
  		return NULL;
  	return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
  }
  
  static inline void free_mm_slot(struct mm_slot *mm_slot)
  {
  	kmem_cache_free(mm_slot_cache, mm_slot);
  }
  
  static int __init mm_slots_hash_init(void)
  {
  	mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head),
  				GFP_KERNEL);
  	if (!mm_slots_hash)
  		return -ENOMEM;
  	return 0;
  }
  
  #if 0
  static void __init mm_slots_hash_free(void)
  {
  	kfree(mm_slots_hash);
  	mm_slots_hash = NULL;
  }
  #endif
  
  static struct mm_slot *get_mm_slot(struct mm_struct *mm)
  {
  	struct mm_slot *mm_slot;
  	struct hlist_head *bucket;
  	struct hlist_node *node;
  
  	bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
  				% MM_SLOTS_HASH_HEADS];
  	hlist_for_each_entry(mm_slot, node, bucket, hash) {
  		if (mm == mm_slot->mm)
  			return mm_slot;
  	}
  	return NULL;
  }
  
  static void insert_to_mm_slots_hash(struct mm_struct *mm,
  				    struct mm_slot *mm_slot)
  {
  	struct hlist_head *bucket;
  
  	bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
  				% MM_SLOTS_HASH_HEADS];
  	mm_slot->mm = mm;
  	hlist_add_head(&mm_slot->hash, bucket);
  }
  
  static inline int khugepaged_test_exit(struct mm_struct *mm)
  {
  	return atomic_read(&mm->mm_users) == 0;
  }
  
  int __khugepaged_enter(struct mm_struct *mm)
  {
  	struct mm_slot *mm_slot;
  	int wakeup;
  
  	mm_slot = alloc_mm_slot();
  	if (!mm_slot)
  		return -ENOMEM;
  
  	/* __khugepaged_exit() must not run from under us */
  	VM_BUG_ON(khugepaged_test_exit(mm));
  	if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
  		free_mm_slot(mm_slot);
  		return 0;
  	}
  
  	spin_lock(&khugepaged_mm_lock);
  	insert_to_mm_slots_hash(mm, mm_slot);
  	/*
  	 * Insert just behind the scanning cursor, to let the area settle
  	 * down a little.
  	 */
  	wakeup = list_empty(&khugepaged_scan.mm_head);
  	list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
  	spin_unlock(&khugepaged_mm_lock);
  
  	atomic_inc(&mm->mm_count);
  	if (wakeup)
  		wake_up_interruptible(&khugepaged_wait);
  
  	return 0;
  }
  
  int khugepaged_enter_vma_merge(struct vm_area_struct *vma)
  {
  	unsigned long hstart, hend;
  	if (!vma->anon_vma)
  		/*
  		 * Not yet faulted in so we will register later in the
  		 * page fault if needed.
  		 */
  		return 0;

  	if (vma->vm_ops)

  		/* khugepaged not yet working on file or special mappings */
  		return 0;

  	/*
  	 * If is_pfn_mapping() is true is_learn_pfn_mapping() must be
  	 * true too, verify it here.
  	 */
  	VM_BUG_ON(is_linear_pfn_mapping(vma) || vma->vm_flags & VM_NO_THP);

  	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
  	hend = vma->vm_end & HPAGE_PMD_MASK;
  	if (hstart < hend)
  		return khugepaged_enter(vma);
  	return 0;
  }
  
  void __khugepaged_exit(struct mm_struct *mm)
  {
  	struct mm_slot *mm_slot;
  	int free = 0;
  
  	spin_lock(&khugepaged_mm_lock);
  	mm_slot = get_mm_slot(mm);
  	if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
  		hlist_del(&mm_slot->hash);
  		list_del(&mm_slot->mm_node);
  		free = 1;
  	}

  	spin_unlock(&khugepaged_mm_lock);

  
  	if (free) {

  		clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
  		free_mm_slot(mm_slot);
  		mmdrop(mm);
  	} else if (mm_slot) {

  		/*
  		 * This is required to serialize against
  		 * khugepaged_test_exit() (which is guaranteed to run
  		 * under mmap sem read mode). Stop here (after we
  		 * return all pagetables will be destroyed) until
  		 * khugepaged has finished working on the pagetables
  		 * under the mmap_sem.
  		 */
  		down_write(&mm->mmap_sem);
  		up_write(&mm->mmap_sem);

  	}

  }
  
  static void release_pte_page(struct page *page)
  {
  	/* 0 stands for page_is_file_cache(page) == false */
  	dec_zone_page_state(page, NR_ISOLATED_ANON + 0);
  	unlock_page(page);
  	putback_lru_page(page);
  }
  
  static void release_pte_pages(pte_t *pte, pte_t *_pte)
  {
  	while (--_pte >= pte) {
  		pte_t pteval = *_pte;
  		if (!pte_none(pteval))
  			release_pte_page(pte_page(pteval));
  	}
  }
  
  static void release_all_pte_pages(pte_t *pte)
  {
  	release_pte_pages(pte, pte + HPAGE_PMD_NR);
  }
  
  static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
  					unsigned long address,
  					pte_t *pte)
  {
  	struct page *page;
  	pte_t *_pte;
  	int referenced = 0, isolated = 0, none = 0;
  	for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
  	     _pte++, address += PAGE_SIZE) {
  		pte_t pteval = *_pte;
  		if (pte_none(pteval)) {
  			if (++none <= khugepaged_max_ptes_none)
  				continue;
  			else {
  				release_pte_pages(pte, _pte);
  				goto out;
  			}
  		}
  		if (!pte_present(pteval) || !pte_write(pteval)) {
  			release_pte_pages(pte, _pte);
  			goto out;
  		}
  		page = vm_normal_page(vma, address, pteval);
  		if (unlikely(!page)) {
  			release_pte_pages(pte, _pte);
  			goto out;
  		}
  		VM_BUG_ON(PageCompound(page));
  		BUG_ON(!PageAnon(page));
  		VM_BUG_ON(!PageSwapBacked(page));
  
  		/* cannot use mapcount: can't collapse if there's a gup pin */
  		if (page_count(page) != 1) {
  			release_pte_pages(pte, _pte);
  			goto out;
  		}
  		/*
  		 * We can do it before isolate_lru_page because the
  		 * page can't be freed from under us. NOTE: PG_lock
  		 * is needed to serialize against split_huge_page
  		 * when invoked from the VM.
  		 */
  		if (!trylock_page(page)) {
  			release_pte_pages(pte, _pte);
  			goto out;
  		}
  		/*
  		 * Isolate the page to avoid collapsing an hugepage
  		 * currently in use by the VM.
  		 */
  		if (isolate_lru_page(page)) {
  			unlock_page(page);
  			release_pte_pages(pte, _pte);
  			goto out;
  		}
  		/* 0 stands for page_is_file_cache(page) == false */
  		inc_zone_page_state(page, NR_ISOLATED_ANON + 0);
  		VM_BUG_ON(!PageLocked(page));
  		VM_BUG_ON(PageLRU(page));
  
  		/* If there is no mapped pte young don't collapse the page */

  		if (pte_young(pteval) || PageReferenced(page) ||
  		    mmu_notifier_test_young(vma->vm_mm, address))

  			referenced = 1;
  	}
  	if (unlikely(!referenced))
  		release_all_pte_pages(pte);
  	else
  		isolated = 1;
  out:
  	return isolated;
  }
  
  static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
  				      struct vm_area_struct *vma,
  				      unsigned long address,
  				      spinlock_t *ptl)
  {
  	pte_t *_pte;
  	for (_pte = pte; _pte < pte+HPAGE_PMD_NR; _pte++) {
  		pte_t pteval = *_pte;
  		struct page *src_page;
  
  		if (pte_none(pteval)) {
  			clear_user_highpage(page, address);
  			add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
  		} else {
  			src_page = pte_page(pteval);
  			copy_user_highpage(page, src_page, address, vma);
  			VM_BUG_ON(page_mapcount(src_page) != 1);
  			VM_BUG_ON(page_count(src_page) != 2);
  			release_pte_page(src_page);
  			/*
  			 * ptl mostly unnecessary, but preempt has to
  			 * be disabled to update the per-cpu stats
  			 * inside page_remove_rmap().
  			 */
  			spin_lock(ptl);
  			/*
  			 * paravirt calls inside pte_clear here are
  			 * superfluous.
  			 */
  			pte_clear(vma->vm_mm, address, _pte);
  			page_remove_rmap(src_page);
  			spin_unlock(ptl);
  			free_page_and_swap_cache(src_page);
  		}
  
  		address += PAGE_SIZE;
  		page++;
  	}
  }
  
  static void collapse_huge_page(struct mm_struct *mm,
  			       unsigned long address,

  			       struct page **hpage,

  			       struct vm_area_struct *vma,
  			       int node)

  {

  	pgd_t *pgd;
  	pud_t *pud;
  	pmd_t *pmd, _pmd;
  	pte_t *pte;
  	pgtable_t pgtable;
  	struct page *new_page;
  	spinlock_t *ptl;
  	int isolated;
  	unsigned long hstart, hend;
  
  	VM_BUG_ON(address & ~HPAGE_PMD_MASK);

  #ifndef CONFIG_NUMA

  	up_read(&mm->mmap_sem);

  	VM_BUG_ON(!*hpage);

  	new_page = *hpage;

  #else
  	VM_BUG_ON(*hpage);

  	/*
  	 * Allocate the page while the vma is still valid and under
  	 * the mmap_sem read mode so there is no memory allocation
  	 * later when we take the mmap_sem in write mode. This is more
  	 * friendly behavior (OTOH it may actually hide bugs) to
  	 * filesystems in userland with daemons allocating memory in
  	 * the userland I/O paths.  Allocating memory with the
  	 * mmap_sem in read mode is good idea also to allow greater
  	 * scalability.
  	 */

  	new_page = alloc_hugepage_vma(khugepaged_defrag(), vma, address,

  				      node, __GFP_OTHER_NODE);

  
  	/*
  	 * After allocating the hugepage, release the mmap_sem read lock in
  	 * preparation for taking it in write mode.
  	 */
  	up_read(&mm->mmap_sem);

  	if (unlikely(!new_page)) {

  		count_vm_event(THP_COLLAPSE_ALLOC_FAILED);

  		*hpage = ERR_PTR(-ENOMEM);
  		return;
  	}

  #endif

  	count_vm_event(THP_COLLAPSE_ALLOC);

  	if (unlikely(mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL))) {

  #ifdef CONFIG_NUMA

  		put_page(new_page);

  #endif

  		return;
  	}

  
  	/*
  	 * Prevent all access to pagetables with the exception of
  	 * gup_fast later hanlded by the ptep_clear_flush and the VM
  	 * handled by the anon_vma lock + PG_lock.
  	 */
  	down_write(&mm->mmap_sem);
  	if (unlikely(khugepaged_test_exit(mm)))
  		goto out;
  
  	vma = find_vma(mm, address);
  	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
  	hend = vma->vm_end & HPAGE_PMD_MASK;
  	if (address < hstart || address + HPAGE_PMD_SIZE > hend)
  		goto out;

  	if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
  	    (vma->vm_flags & VM_NOHUGEPAGE))

  		goto out;

  	if (!vma->anon_vma || vma->vm_ops)

  		goto out;

  	if (is_vma_temporary_stack(vma))
  		goto out;

  	/*
  	 * If is_pfn_mapping() is true is_learn_pfn_mapping() must be
  	 * true too, verify it here.
  	 */
  	VM_BUG_ON(is_linear_pfn_mapping(vma) || vma->vm_flags & VM_NO_THP);

  
  	pgd = pgd_offset(mm, address);
  	if (!pgd_present(*pgd))
  		goto out;
  
  	pud = pud_offset(pgd, address);
  	if (!pud_present(*pud))
  		goto out;
  
  	pmd = pmd_offset(pud, address);
  	/* pmd can't go away or become huge under us */
  	if (!pmd_present(*pmd) || pmd_trans_huge(*pmd))
  		goto out;

  	anon_vma_lock(vma->anon_vma);
  
  	pte = pte_offset_map(pmd, address);
  	ptl = pte_lockptr(mm, pmd);
  
  	spin_lock(&mm->page_table_lock); /* probably unnecessary */
  	/*
  	 * After this gup_fast can't run anymore. This also removes
  	 * any huge TLB entry from the CPU so we won't allow
  	 * huge and small TLB entries for the same virtual address
  	 * to avoid the risk of CPU bugs in that area.
  	 */
  	_pmd = pmdp_clear_flush_notify(vma, address, pmd);
  	spin_unlock(&mm->page_table_lock);
  
  	spin_lock(ptl);
  	isolated = __collapse_huge_page_isolate(vma, address, pte);
  	spin_unlock(ptl);

  
  	if (unlikely(!isolated)) {

  		pte_unmap(pte);

  		spin_lock(&mm->page_table_lock);
  		BUG_ON(!pmd_none(*pmd));
  		set_pmd_at(mm, address, pmd, _pmd);
  		spin_unlock(&mm->page_table_lock);
  		anon_vma_unlock(vma->anon_vma);

  		goto out;

  	}
  
  	/*
  	 * All pages are isolated and locked so anon_vma rmap
  	 * can't run anymore.
  	 */
  	anon_vma_unlock(vma->anon_vma);
  
  	__collapse_huge_page_copy(pte, new_page, vma, address, ptl);

  	pte_unmap(pte);

  	__SetPageUptodate(new_page);
  	pgtable = pmd_pgtable(_pmd);
  	VM_BUG_ON(page_count(pgtable) != 1);
  	VM_BUG_ON(page_mapcount(pgtable) != 0);
  
  	_pmd = mk_pmd(new_page, vma->vm_page_prot);
  	_pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
  	_pmd = pmd_mkhuge(_pmd);
  
  	/*
  	 * spin_lock() below is not the equivalent of smp_wmb(), so
  	 * this is needed to avoid the copy_huge_page writes to become
  	 * visible after the set_pmd_at() write.
  	 */
  	smp_wmb();
  
  	spin_lock(&mm->page_table_lock);
  	BUG_ON(!pmd_none(*pmd));
  	page_add_new_anon_rmap(new_page, vma, address);
  	set_pmd_at(mm, address, pmd, _pmd);

  	update_mmu_cache(vma, address, _pmd);

  	prepare_pmd_huge_pte(pgtable, mm);
  	mm->nr_ptes--;
  	spin_unlock(&mm->page_table_lock);

  #ifndef CONFIG_NUMA

  	*hpage = NULL;

  #endif

  	khugepaged_pages_collapsed++;

  out_up_write:

  	up_write(&mm->mmap_sem);

  	return;

  out:

  	mem_cgroup_uncharge_page(new_page);

  #ifdef CONFIG_NUMA
  	put_page(new_page);
  #endif

  	goto out_up_write;

  }
  
  static int khugepaged_scan_pmd(struct mm_struct *mm,
  			       struct vm_area_struct *vma,
  			       unsigned long address,
  			       struct page **hpage)
  {
  	pgd_t *pgd;
  	pud_t *pud;
  	pmd_t *pmd;
  	pte_t *pte, *_pte;
  	int ret = 0, referenced = 0, none = 0;
  	struct page *page;
  	unsigned long _address;
  	spinlock_t *ptl;

  	int node = -1;

  
  	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
  
  	pgd = pgd_offset(mm, address);
  	if (!pgd_present(*pgd))
  		goto out;
  
  	pud = pud_offset(pgd, address);
  	if (!pud_present(*pud))
  		goto out;
  
  	pmd = pmd_offset(pud, address);
  	if (!pmd_present(*pmd) || pmd_trans_huge(*pmd))
  		goto out;
  
  	pte = pte_offset_map_lock(mm, pmd, address, &ptl);
  	for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
  	     _pte++, _address += PAGE_SIZE) {
  		pte_t pteval = *_pte;
  		if (pte_none(pteval)) {
  			if (++none <= khugepaged_max_ptes_none)
  				continue;
  			else
  				goto out_unmap;
  		}
  		if (!pte_present(pteval) || !pte_write(pteval))
  			goto out_unmap;
  		page = vm_normal_page(vma, _address, pteval);
  		if (unlikely(!page))
  			goto out_unmap;

  		/*
  		 * Chose the node of the first page. This could
  		 * be more sophisticated and look at more pages,
  		 * but isn't for now.
  		 */
  		if (node == -1)
  			node = page_to_nid(page);

  		VM_BUG_ON(PageCompound(page));
  		if (!PageLRU(page) || PageLocked(page) || !PageAnon(page))
  			goto out_unmap;
  		/* cannot use mapcount: can't collapse if there's a gup pin */
  		if (page_count(page) != 1)
  			goto out_unmap;

  		if (pte_young(pteval) || PageReferenced(page) ||
  		    mmu_notifier_test_young(vma->vm_mm, address))

  			referenced = 1;
  	}
  	if (referenced)
  		ret = 1;
  out_unmap:
  	pte_unmap_unlock(pte, ptl);

  	if (ret)
  		/* collapse_huge_page will return with the mmap_sem released */

  		collapse_huge_page(mm, address, hpage, vma, node);

  out:
  	return ret;
  }
  
  static void collect_mm_slot(struct mm_slot *mm_slot)
  {
  	struct mm_struct *mm = mm_slot->mm;
  
  	VM_BUG_ON(!spin_is_locked(&khugepaged_mm_lock));
  
  	if (khugepaged_test_exit(mm)) {
  		/* free mm_slot */
  		hlist_del(&mm_slot->hash);
  		list_del(&mm_slot->mm_node);
  
  		/*
  		 * Not strictly needed because the mm exited already.
  		 *
  		 * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
  		 */
  
  		/* khugepaged_mm_lock actually not necessary for the below */
  		free_mm_slot(mm_slot);
  		mmdrop(mm);
  	}
  }
  
  static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
  					    struct page **hpage)

  	__releases(&khugepaged_mm_lock)
  	__acquires(&khugepaged_mm_lock)

  {
  	struct mm_slot *mm_slot;
  	struct mm_struct *mm;
  	struct vm_area_struct *vma;
  	int progress = 0;
  
  	VM_BUG_ON(!pages);
  	VM_BUG_ON(!spin_is_locked(&khugepaged_mm_lock));
  
  	if (khugepaged_scan.mm_slot)
  		mm_slot = khugepaged_scan.mm_slot;
  	else {
  		mm_slot = list_entry(khugepaged_scan.mm_head.next,
  				     struct mm_slot, mm_node);
  		khugepaged_scan.address = 0;
  		khugepaged_scan.mm_slot = mm_slot;
  	}
  	spin_unlock(&khugepaged_mm_lock);
  
  	mm = mm_slot->mm;
  	down_read(&mm->mmap_sem);
  	if (unlikely(khugepaged_test_exit(mm)))
  		vma = NULL;
  	else
  		vma = find_vma(mm, khugepaged_scan.address);
  
  	progress++;
  	for (; vma; vma = vma->vm_next) {
  		unsigned long hstart, hend;
  
  		cond_resched();
  		if (unlikely(khugepaged_test_exit(mm))) {
  			progress++;
  			break;
  		}

  		if ((!(vma->vm_flags & VM_HUGEPAGE) &&
  		     !khugepaged_always()) ||
  		    (vma->vm_flags & VM_NOHUGEPAGE)) {

  		skip:

  			progress++;
  			continue;
  		}

  		if (!vma->anon_vma || vma->vm_ops)

  			goto skip;
  		if (is_vma_temporary_stack(vma))
  			goto skip;

  		/*
  		 * If is_pfn_mapping() is true is_learn_pfn_mapping()
  		 * must be true too, verify it here.
  		 */
  		VM_BUG_ON(is_linear_pfn_mapping(vma) ||
  			  vma->vm_flags & VM_NO_THP);

  
  		hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
  		hend = vma->vm_end & HPAGE_PMD_MASK;

  		if (hstart >= hend)
  			goto skip;
  		if (khugepaged_scan.address > hend)
  			goto skip;

  		if (khugepaged_scan.address < hstart)
  			khugepaged_scan.address = hstart;

  		VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);

  
  		while (khugepaged_scan.address < hend) {
  			int ret;
  			cond_resched();
  			if (unlikely(khugepaged_test_exit(mm)))
  				goto breakouterloop;
  
  			VM_BUG_ON(khugepaged_scan.address < hstart ||
  				  khugepaged_scan.address + HPAGE_PMD_SIZE >
  				  hend);
  			ret = khugepaged_scan_pmd(mm, vma,
  						  khugepaged_scan.address,
  						  hpage);
  			/* move to next address */
  			khugepaged_scan.address += HPAGE_PMD_SIZE;
  			progress += HPAGE_PMD_NR;
  			if (ret)
  				/* we released mmap_sem so break loop */
  				goto breakouterloop_mmap_sem;
  			if (progress >= pages)
  				goto breakouterloop;
  		}
  	}
  breakouterloop:
  	up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
  breakouterloop_mmap_sem:
  
  	spin_lock(&khugepaged_mm_lock);

  	VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);

  	/*
  	 * Release the current mm_slot if this mm is about to die, or
  	 * if we scanned all vmas of this mm.
  	 */
  	if (khugepaged_test_exit(mm) || !vma) {
  		/*
  		 * Make sure that if mm_users is reaching zero while
  		 * khugepaged runs here, khugepaged_exit will find
  		 * mm_slot not pointing to the exiting mm.
  		 */
  		if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
  			khugepaged_scan.mm_slot = list_entry(
  				mm_slot->mm_node.next,
  				struct mm_slot, mm_node);
  			khugepaged_scan.address = 0;
  		} else {
  			khugepaged_scan.mm_slot = NULL;
  			khugepaged_full_scans++;
  		}
  
  		collect_mm_slot(mm_slot);
  	}
  
  	return progress;
  }
  
  static int khugepaged_has_work(void)
  {
  	return !list_empty(&khugepaged_scan.mm_head) &&
  		khugepaged_enabled();
  }
  
  static int khugepaged_wait_event(void)
  {
  	return !list_empty(&khugepaged_scan.mm_head) ||
  		!khugepaged_enabled();
  }
  
  static void khugepaged_do_scan(struct page **hpage)
  {
  	unsigned int progress = 0, pass_through_head = 0;
  	unsigned int pages = khugepaged_pages_to_scan;
  
  	barrier(); /* write khugepaged_pages_to_scan to local stack */
  
  	while (progress < pages) {
  		cond_resched();

  #ifndef CONFIG_NUMA

  		if (!*hpage) {
  			*hpage = alloc_hugepage(khugepaged_defrag());

  			if (unlikely(!*hpage)) {
  				count_vm_event(THP_COLLAPSE_ALLOC_FAILED);

  				break;

  			}
  			count_vm_event(THP_COLLAPSE_ALLOC);

  		}

  #else
  		if (IS_ERR(*hpage))
  			break;
  #endif

  		if (unlikely(kthread_should_stop() || freezing(current)))
  			break;

  		spin_lock(&khugepaged_mm_lock);
  		if (!khugepaged_scan.mm_slot)
  			pass_through_head++;
  		if (khugepaged_has_work() &&
  		    pass_through_head < 2)
  			progress += khugepaged_scan_mm_slot(pages - progress,
  							    hpage);
  		else
  			progress = pages;
  		spin_unlock(&khugepaged_mm_lock);
  	}
  }

  static void khugepaged_alloc_sleep(void)
  {

  	wait_event_freezable_timeout(khugepaged_wait, false,
  			msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));

  }
  
  #ifndef CONFIG_NUMA

  static struct page *khugepaged_alloc_hugepage(void)
  {
  	struct page *hpage;
  
  	do {
  		hpage = alloc_hugepage(khugepaged_defrag());

  		if (!hpage) {
  			count_vm_event(THP_COLLAPSE_ALLOC_FAILED);

  			khugepaged_alloc_sleep();

  		} else
  			count_vm_event(THP_COLLAPSE_ALLOC);

  	} while (unlikely(!hpage) &&
  		 likely(khugepaged_enabled()));
  	return hpage;
  }

  #endif

  
  static void khugepaged_loop(void)
  {
  	struct page *hpage;

  #ifdef CONFIG_NUMA
  	hpage = NULL;
  #endif

  	while (likely(khugepaged_enabled())) {

  #ifndef CONFIG_NUMA

  		hpage = khugepaged_alloc_hugepage();

  		if (unlikely(!hpage))

  			break;

  #else
  		if (IS_ERR(hpage)) {
  			khugepaged_alloc_sleep();
  			hpage = NULL;
  		}
  #endif

  
  		khugepaged_do_scan(&hpage);

  #ifndef CONFIG_NUMA

  		if (hpage)
  			put_page(hpage);

  #endif

  		try_to_freeze();
  		if (unlikely(kthread_should_stop()))
  			break;

  		if (khugepaged_has_work()) {

  			if (!khugepaged_scan_sleep_millisecs)
  				continue;

  			wait_event_freezable_timeout(khugepaged_wait, false,
  			    msecs_to_jiffies(khugepaged_scan_sleep_millisecs));

  		} else if (khugepaged_enabled())

  			wait_event_freezable(khugepaged_wait,
  					     khugepaged_wait_event());

  	}
  }
  
  static int khugepaged(void *none)
  {
  	struct mm_slot *mm_slot;

  	set_freezable();

  	set_user_nice(current, 19);
  
  	/* serialize with start_khugepaged() */
  	mutex_lock(&khugepaged_mutex);
  
  	for (;;) {
  		mutex_unlock(&khugepaged_mutex);

  		VM_BUG_ON(khugepaged_thread != current);

  		khugepaged_loop();

  		VM_BUG_ON(khugepaged_thread != current);

  
  		mutex_lock(&khugepaged_mutex);
  		if (!khugepaged_enabled())
  			break;

  		if (unlikely(kthread_should_stop()))
  			break;

  	}
  
  	spin_lock(&khugepaged_mm_lock);
  	mm_slot = khugepaged_scan.mm_slot;
  	khugepaged_scan.mm_slot = NULL;
  	if (mm_slot)
  		collect_mm_slot(mm_slot);
  	spin_unlock(&khugepaged_mm_lock);
  
  	khugepaged_thread = NULL;
  	mutex_unlock(&khugepaged_mutex);
  
  	return 0;
  }

  void __split_huge_page_pmd(struct mm_struct *mm, pmd_t *pmd)
  {
  	struct page *page;
  
  	spin_lock(&mm->page_table_lock);
  	if (unlikely(!pmd_trans_huge(*pmd))) {
  		spin_unlock(&mm->page_table_lock);
  		return;
  	}
  	page = pmd_page(*pmd);
  	VM_BUG_ON(!page_count(page));
  	get_page(page);
  	spin_unlock(&mm->page_table_lock);
  
  	split_huge_page(page);
  
  	put_page(page);
  	BUG_ON(pmd_trans_huge(*pmd));
  }

  
  static void split_huge_page_address(struct mm_struct *mm,
  				    unsigned long address)
  {
  	pgd_t *pgd;
  	pud_t *pud;
  	pmd_t *pmd;
  
  	VM_BUG_ON(!(address & ~HPAGE_PMD_MASK));
  
  	pgd = pgd_offset(mm, address);
  	if (!pgd_present(*pgd))
  		return;
  
  	pud = pud_offset(pgd, address);
  	if (!pud_present(*pud))
  		return;
  
  	pmd = pmd_offset(pud, address);
  	if (!pmd_present(*pmd))
  		return;
  	/*
  	 * Caller holds the mmap_sem write mode, so a huge pmd cannot
  	 * materialize from under us.
  	 */
  	split_huge_page_pmd(mm, pmd);
  }
  
  void __vma_adjust_trans_huge(struct vm_area_struct *vma,
  			     unsigned long start,
  			     unsigned long end,
  			     long adjust_next)
  {
  	/*
  	 * If the new start address isn't hpage aligned and it could
  	 * previously contain an hugepage: check if we need to split
  	 * an huge pmd.
  	 */
  	if (start & ~HPAGE_PMD_MASK &&
  	    (start & HPAGE_PMD_MASK) >= vma->vm_start &&
  	    (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
  		split_huge_page_address(vma->vm_mm, start);
  
  	/*
  	 * If the new end address isn't hpage aligned and it could
  	 * previously contain an hugepage: check if we need to split
  	 * an huge pmd.
  	 */
  	if (end & ~HPAGE_PMD_MASK &&
  	    (end & HPAGE_PMD_MASK) >= vma->vm_start &&
  	    (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
  		split_huge_page_address(vma->vm_mm, end);
  
  	/*
  	 * If we're also updating the vma->vm_next->vm_start, if the new
  	 * vm_next->vm_start isn't page aligned and it could previously
  	 * contain an hugepage: check if we need to split an huge pmd.
  	 */
  	if (adjust_next > 0) {
  		struct vm_area_struct *next = vma->vm_next;
  		unsigned long nstart = next->vm_start;
  		nstart += adjust_next << PAGE_SHIFT;
  		if (nstart & ~HPAGE_PMD_MASK &&
  		    (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
  		    (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
  			split_huge_page_address(next->vm_mm, nstart);
  	}
  }