Initial import

1 files changed, 3011 insertions, 0 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
new file mode 100644
index 000000000..078832cf3
--- /dev/null
+++ b/mm/huge_memory.c
@@ -0,0 +1,3011 @@
+/*
+ *  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.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#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/shrinker.h>
+#include <linux/mm_inline.h>
+#include <linux/kthread.h>
+#include <linux/khugepaged.h>
+#include <linux/freezer.h>
+#include <linux/mman.h>
+#include <linux/pagemap.h>
+#include <linux/migrate.h>
+#include <linux/hashtable.h>
+
+#include <asm/tlb.h>
+#include <asm/pgalloc.h>
+#include "internal.h"
+
+/*
+ * By default transparent hugepage support is disabled in order that avoid
+ * to risk increase the memory footprint of applications without a guaranteed
+ * benefit. When transparent hugepage support is enabled, is for all mappings,
+ * and khugepaged scans all mappings.
+ * Defrag is invoked by khugepaged hugepage allocations and by page faults
+ * for all hugepage 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)|
+	(1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_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 khugepaged_slab_init(void);
+static void khugepaged_slab_exit(void);
+
+#define MM_SLOTS_HASH_BITS 10
+static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
+
+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;
+
+	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) {
+		if (user_min_free_kbytes >= 0)
+			pr_info("raising min_free_kbytes from %d to %lu "
+				"to help transparent hugepage allocations\n",
+				min_free_kbytes, recommended_min);
+
+		min_free_kbytes = recommended_min;
+	}
+	setup_per_zone_wmarks();
+	return 0;
+}
+
+static int start_stop_khugepaged(void)
+{
+	int err = 0;
+	if (khugepaged_enabled()) {
+		if (!khugepaged_thread)
+			khugepaged_thread = kthread_run(khugepaged, NULL,
+							"khugepaged");
+		if (unlikely(IS_ERR(khugepaged_thread))) {
+			pr_err("khugepaged: kthread_run(khugepaged) failed\n");
+			err = PTR_ERR(khugepaged_thread);
+			khugepaged_thread = NULL;
+			goto fail;
+		}
+
+		if (!list_empty(&khugepaged_scan.mm_head))
+			wake_up_interruptible(&khugepaged_wait);
+
+		set_recommended_min_free_kbytes();
+	} else if (khugepaged_thread) {
+		kthread_stop(khugepaged_thread);
+		khugepaged_thread = NULL;
+	}
+fail:
+	return err;
+}
+
+static atomic_t huge_zero_refcount;
+struct page *huge_zero_page __read_mostly;
+
+static inline bool is_huge_zero_pmd(pmd_t pmd)
+{
+	return is_huge_zero_page(pmd_page(pmd));
+}
+
+static struct page *get_huge_zero_page(void)
+{
+	struct page *zero_page;
+retry:
+	if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
+		return READ_ONCE(huge_zero_page);
+
+	zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
+			HPAGE_PMD_ORDER);
+	if (!zero_page) {
+		count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
+		return NULL;
+	}
+	count_vm_event(THP_ZERO_PAGE_ALLOC);
+	preempt_disable();
+	if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
+		preempt_enable();
+		__free_pages(zero_page, compound_order(zero_page));
+		goto retry;
+	}
+
+	/* We take additional reference here. It will be put back by shrinker */
+	atomic_set(&huge_zero_refcount, 2);
+	preempt_enable();
+	return READ_ONCE(huge_zero_page);
+}
+
+static void put_huge_zero_page(void)
+{
+	/*
+	 * Counter should never go to zero here. Only shrinker can put
+	 * last reference.
+	 */
+	BUG_ON(atomic_dec_and_test(&huge_zero_refcount));
+}
+
+static unsigned long shrink_huge_zero_page_count(struct shrinker *shrink,
+					struct shrink_control *sc)
+{
+	/* we can free zero page only if last reference remains */
+	return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0;
+}
+
+static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
+				       struct shrink_control *sc)
+{
+	if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
+		struct page *zero_page = xchg(&huge_zero_page, NULL);
+		BUG_ON(zero_page == NULL);
+		__free_pages(zero_page, compound_order(zero_page));
+		return HPAGE_PMD_NR;
+	}
+
+	return 0;
+}
+
+static struct shrinker huge_zero_page_shrinker = {
+	.count_objects = shrink_huge_zero_page_count,
+	.scan_objects = shrink_huge_zero_page_scan,
+	.seeks = DEFAULT_SEEKS,
+};
+
+#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\n");
+	} else if (test_bit(req_madv, &transparent_hugepage_flags))
+		return sprintf(buf, "always [madvise] never\n");
+	else
+		return sprintf(buf, "always madvise [never]\n");
+}
+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;
+
+		mutex_lock(&khugepaged_mutex);
+		err = start_stop_khugepaged();
+		mutex_unlock(&khugepaged_mutex);
+
+		if (err)
+			ret = err;
+	}
+
+	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\n",
+		       !!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);
+
+static ssize_t use_zero_page_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	return single_flag_show(kobj, attr, buf,
+				TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
+}
+static ssize_t use_zero_page_store(struct kobject *kobj,
+		struct kobj_attribute *attr, const char *buf, size_t count)
+{
+	return single_flag_store(kobj, attr, buf, count,
+				 TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
+}
+static struct kobj_attribute use_zero_page_attr =
+	__ATTR(use_zero_page, 0644, use_zero_page_show, use_zero_page_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,
+	&use_zero_page_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\n", 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 = kstrtoul(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\n", 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 = kstrtoul(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\n", 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 = kstrtoul(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\n", 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\n", 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\n", 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 = kstrtoul(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)) {
+		pr_err("failed to create transparent hugepage kobject\n");
+		return -ENOMEM;
+	}
+
+	err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);
+	if (err) {
+		pr_err("failed to register transparent hugepage group\n");
+		goto delete_obj;
+	}
+
+	err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);
+	if (err) {
+		pr_err("failed to register transparent hugepage group\n");
+		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)
+		goto err_sysfs;
+
+	err = khugepaged_slab_init();
+	if (err)
+		goto err_slab;
+
+	err = register_shrinker(&huge_zero_page_shrinker);
+	if (err)
+		goto err_hzp_shrinker;
+
+	/*
+	 * 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;
+		return 0;
+	}
+
+	err = start_stop_khugepaged();
+	if (err)
+		goto err_khugepaged;
+
+	return 0;
+err_khugepaged:
+	unregister_shrinker(&huge_zero_page_shrinker);
+err_hzp_shrinker:
+	khugepaged_slab_exit();
+err_slab:
+	hugepage_exit_sysfs(hugepage_kobj);
+err_sysfs:
+	return err;
+}
+subsys_initcall(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)
+		pr_warn("transparent_hugepage= cannot parse, ignored\n");
+	return ret;
+}
+__setup("transparent_hugepage=", setup_transparent_hugepage);
+
+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 inline pmd_t mk_huge_pmd(struct page *page, pgprot_t prot)
+{
+	pmd_t entry;
+	entry = mk_pmd(page, prot);
+	entry = pmd_mkhuge(entry);
+	return entry;
+}
+
+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, gfp_t gfp)
+{
+	struct mem_cgroup *memcg;
+	pgtable_t pgtable;
+	spinlock_t *ptl;
+
+	VM_BUG_ON_PAGE(!PageCompound(page), page);
+
+	if (mem_cgroup_try_charge(page, mm, gfp, &memcg))
+		return VM_FAULT_OOM;
+
+	pgtable = pte_alloc_one(mm, haddr);
+	if (unlikely(!pgtable)) {
+		mem_cgroup_cancel_charge(page, memcg);
+		return VM_FAULT_OOM;
+	}
+
+	clear_huge_page(page, haddr, HPAGE_PMD_NR);
+	/*
+	 * The memory barrier inside __SetPageUptodate makes sure that
+	 * clear_huge_page writes become visible before the set_pmd_at()
+	 * write.
+	 */
+	__SetPageUptodate(page);
+
+	ptl = pmd_lock(mm, pmd);
+	if (unlikely(!pmd_none(*pmd))) {
+		spin_unlock(ptl);
+		mem_cgroup_cancel_charge(page, memcg);
+		put_page(page);
+		pte_free(mm, pgtable);
+	} else {
+		pmd_t entry;
+		entry = mk_huge_pmd(page, vma->vm_page_prot);
+		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
+		page_add_new_anon_rmap(page, vma, haddr);
+		mem_cgroup_commit_charge(page, memcg, false);
+		lru_cache_add_active_or_unevictable(page, vma);
+		pgtable_trans_huge_deposit(mm, pmd, pgtable);
+		set_pmd_at(mm, haddr, pmd, entry);
+		add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
+		atomic_long_inc(&mm->nr_ptes);
+		spin_unlock(ptl);
+	}
+
+	return 0;
+}
+
+static inline gfp_t alloc_hugepage_gfpmask(int defrag, gfp_t extra_gfp)
+{
+	return (GFP_TRANSHUGE & ~(defrag ? 0 : __GFP_WAIT)) | extra_gfp;
+}
+
+/* Caller must hold page table lock. */
+static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
+		struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
+		struct page *zero_page)
+{
+	pmd_t entry;
+	if (!pmd_none(*pmd))
+		return false;
+	entry = mk_pmd(zero_page, vma->vm_page_prot);
+	entry = pmd_mkhuge(entry);
+	pgtable_trans_huge_deposit(mm, pmd, pgtable);
+	set_pmd_at(mm, haddr, pmd, entry);
+	atomic_long_inc(&mm->nr_ptes);
+	return true;
+}
+
+int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
+			       unsigned long address, pmd_t *pmd,
+			       unsigned int flags)
+{
+	gfp_t gfp;
+	struct page *page;
+	unsigned long haddr = address & HPAGE_PMD_MASK;
+
+	if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end)
+		return VM_FAULT_FALLBACK;
+	if (unlikely(anon_vma_prepare(vma)))
+		return VM_FAULT_OOM;
+	if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
+		return VM_FAULT_OOM;
+	if (!(flags & FAULT_FLAG_WRITE) && !mm_forbids_zeropage(mm) &&
+			transparent_hugepage_use_zero_page()) {
+		spinlock_t *ptl;
+		pgtable_t pgtable;
+		struct page *zero_page;
+		bool set;
+		pgtable = pte_alloc_one(mm, haddr);
+		if (unlikely(!pgtable))
+			return VM_FAULT_OOM;
+		zero_page = get_huge_zero_page();
+		if (unlikely(!zero_page)) {
+			pte_free(mm, pgtable);
+			count_vm_event(THP_FAULT_FALLBACK);
+			return VM_FAULT_FALLBACK;
+		}
+		ptl = pmd_lock(mm, pmd);
+		set = set_huge_zero_page(pgtable, mm, vma, haddr, pmd,
+				zero_page);
+		spin_unlock(ptl);
+		if (!set) {
+			pte_free(mm, pgtable);
+			put_huge_zero_page();
+		}
+		return 0;
+	}
+	gfp = alloc_hugepage_gfpmask(transparent_hugepage_defrag(vma), 0);
+	page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
+	if (unlikely(!page)) {
+		count_vm_event(THP_FAULT_FALLBACK);
+		return VM_FAULT_FALLBACK;
+	}
+	if (unlikely(__do_huge_pmd_anonymous_page(mm, vma, haddr, pmd, page, gfp))) {
+		put_page(page);
+		count_vm_event(THP_FAULT_FALLBACK);
+		return VM_FAULT_FALLBACK;
+	}
+
+	count_vm_event(THP_FAULT_ALLOC);
+	return 0;
+}
+
+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)
+{
+	spinlock_t *dst_ptl, *src_ptl;
+	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;
+
+	dst_ptl = pmd_lock(dst_mm, dst_pmd);
+	src_ptl = pmd_lockptr(src_mm, src_pmd);
+	spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
+
+	ret = -EAGAIN;
+	pmd = *src_pmd;
+	if (unlikely(!pmd_trans_huge(pmd))) {
+		pte_free(dst_mm, pgtable);
+		goto out_unlock;
+	}
+	/*
+	 * When page table lock is held, the huge zero pmd should not be
+	 * under splitting since we don't split the page itself, only pmd to
+	 * a page table.
+	 */
+	if (is_huge_zero_pmd(pmd)) {
+		struct page *zero_page;
+		bool set;
+		/*
+		 * get_huge_zero_page() will never allocate a new page here,
+		 * since we already have a zero page to copy. It just takes a
+		 * reference.
+		 */
+		zero_page = get_huge_zero_page();
+		set = set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
+				zero_page);
+		BUG_ON(!set); /* unexpected !pmd_none(dst_pmd) */
+		ret = 0;
+		goto out_unlock;
+	}
+
+	if (unlikely(pmd_trans_splitting(pmd))) {
+		/* split huge page running from under us */
+		spin_unlock(src_ptl);
+		spin_unlock(dst_ptl);
+		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_PAGE(!PageHead(src_page), 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));
+	pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
+	set_pmd_at(dst_mm, addr, dst_pmd, pmd);
+	atomic_long_inc(&dst_mm->nr_ptes);
+
+	ret = 0;
+out_unlock:
+	spin_unlock(src_ptl);
+	spin_unlock(dst_ptl);
+out:
+	return ret;
+}
+
+void huge_pmd_set_accessed(struct mm_struct *mm,
+			   struct vm_area_struct *vma,
+			   unsigned long address,
+			   pmd_t *pmd, pmd_t orig_pmd,
+			   int dirty)
+{
+	spinlock_t *ptl;
+	pmd_t entry;
+	unsigned long haddr;
+
+	ptl = pmd_lock(mm, pmd);
+	if (unlikely(!pmd_same(*pmd, orig_pmd)))
+		goto unlock;
+
+	entry = pmd_mkyoung(orig_pmd);
+	haddr = address & HPAGE_PMD_MASK;
+	if (pmdp_set_access_flags(vma, haddr, pmd, entry, dirty))
+		update_mmu_cache_pmd(vma, address, pmd);
+
+unlock:
+	spin_unlock(ptl);
+}
+
+/*
+ * Save CONFIG_DEBUG_PAGEALLOC from faulting falsely on tail pages
+ * during copy_user_huge_page()'s copy_page_rep(): in the case when
+ * the source page gets split and a tail freed before copy completes.
+ * Called under pmd_lock of checked pmd, so safe from splitting itself.
+ */
+static void get_user_huge_page(struct page *page)
+{
+	if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
+		struct page *endpage = page + HPAGE_PMD_NR;
+
+		atomic_add(HPAGE_PMD_NR, &page->_count);
+		while (++page < endpage)
+			get_huge_page_tail(page);
+	} else {
+		get_page(page);
+	}
+}
+
+static void put_user_huge_page(struct page *page)
+{
+	if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
+		struct page *endpage = page + HPAGE_PMD_NR;
+
+		while (page < endpage)
+			put_page(page++);
+	} else {
+		put_page(page);
+	}
+}
+
+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)
+{
+	struct mem_cgroup *memcg;
+	spinlock_t *ptl;
+	pgtable_t pgtable;
+	pmd_t _pmd;
+	int ret = 0, i;
+	struct page **pages;
+	unsigned long mmun_start;	/* For mmu_notifiers */
+	unsigned long mmun_end;		/* For mmu_notifiers */
+
+	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_try_charge(pages[i], mm, GFP_KERNEL,
+						   &memcg))) {
+			if (pages[i])
+				put_page(pages[i]);
+			while (--i >= 0) {
+				memcg = (void *)page_private(pages[i]);
+				set_page_private(pages[i], 0);
+				mem_cgroup_cancel_charge(pages[i], memcg);
+				put_page(pages[i]);
+			}
+			kfree(pages);
+			ret |= VM_FAULT_OOM;
+			goto out;
+		}
+		set_page_private(pages[i], (unsigned long)memcg);
+	}
+
+	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();
+	}
+
+	mmun_start = haddr;
+	mmun_end   = haddr + HPAGE_PMD_SIZE;
+	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
+
+	ptl = pmd_lock(mm, pmd);
+	if (unlikely(!pmd_same(*pmd, orig_pmd)))
+		goto out_free_pages;
+	VM_BUG_ON_PAGE(!PageHead(page), page);
+
+	pmdp_clear_flush_notify(vma, haddr, pmd);
+	/* leave pmd empty until pte is filled */
+
+	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
+	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);
+		memcg = (void *)page_private(pages[i]);
+		set_page_private(pages[i], 0);
+		page_add_new_anon_rmap(pages[i], vma, haddr);
+		mem_cgroup_commit_charge(pages[i], memcg, false);
+		lru_cache_add_active_or_unevictable(pages[i], vma);
+		pte = pte_offset_map(&_pmd, haddr);
+		VM_BUG_ON(!pte_none(*pte));
+		set_pte_at(mm, haddr, pte, entry);
+		pte_unmap(pte);
+	}
+	kfree(pages);
+
+	smp_wmb(); /* make pte visible before pmd */
+	pmd_populate(mm, pmd, pgtable);
+	page_remove_rmap(page);
+	spin_unlock(ptl);
+
+	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
+
+	ret |= VM_FAULT_WRITE;
+	put_page(page);
+
+out:
+	return ret;
+
+out_free_pages:
+	spin_unlock(ptl);
+	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
+	for (i = 0; i < HPAGE_PMD_NR; i++) {
+		memcg = (void *)page_private(pages[i]);
+		set_page_private(pages[i], 0);
+		mem_cgroup_cancel_charge(pages[i], memcg);
+		put_page(pages[i]);
+	}
+	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)
+{
+	spinlock_t *ptl;
+	int ret = 0;
+	struct page *page = NULL, *new_page;
+	struct mem_cgroup *memcg;
+	unsigned long haddr;
+	unsigned long mmun_start;	/* For mmu_notifiers */
+	unsigned long mmun_end;		/* For mmu_notifiers */
+	gfp_t huge_gfp;			/* for allocation and charge */
+
+	ptl = pmd_lockptr(mm, pmd);
+	VM_BUG_ON_VMA(!vma->anon_vma, vma);
+	haddr = address & HPAGE_PMD_MASK;
+	if (is_huge_zero_pmd(orig_pmd))
+		goto alloc;
+	spin_lock(ptl);
+	if (unlikely(!pmd_same(*pmd, orig_pmd)))
+		goto out_unlock;
+
+	page = pmd_page(orig_pmd);
+	VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
+	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_pmd(vma, address, pmd);
+		ret |= VM_FAULT_WRITE;
+		goto out_unlock;
+	}
+	get_user_huge_page(page);
+	spin_unlock(ptl);
+alloc:
+	if (transparent_hugepage_enabled(vma) &&
+	    !transparent_hugepage_debug_cow()) {
+		huge_gfp = alloc_hugepage_gfpmask(transparent_hugepage_defrag(vma), 0);
+		new_page = alloc_hugepage_vma(huge_gfp, vma, haddr, HPAGE_PMD_ORDER);
+	} else
+		new_page = NULL;
+
+	if (unlikely(!new_page)) {
+		if (!page) {
+			split_huge_page_pmd(vma, address, pmd);
+			ret |= VM_FAULT_FALLBACK;
+		} else {
+			ret = do_huge_pmd_wp_page_fallback(mm, vma, address,
+					pmd, orig_pmd, page, haddr);
+			if (ret & VM_FAULT_OOM) {
+				split_huge_page(page);
+				ret |= VM_FAULT_FALLBACK;
+			}
+			put_user_huge_page(page);
+		}
+		count_vm_event(THP_FAULT_FALLBACK);
+		goto out;
+	}
+
+	if (unlikely(mem_cgroup_try_charge(new_page, mm, huge_gfp, &memcg))) {
+		put_page(new_page);
+		if (page) {
+			split_huge_page(page);
+			put_user_huge_page(page);
+		} else
+			split_huge_page_pmd(vma, address, pmd);
+		ret |= VM_FAULT_FALLBACK;
+		count_vm_event(THP_FAULT_FALLBACK);
+		goto out;
+	}
+
+	count_vm_event(THP_FAULT_ALLOC);
+
+	if (!page)
+		clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
+	else
+		copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
+	__SetPageUptodate(new_page);
+
+	mmun_start = haddr;
+	mmun_end   = haddr + HPAGE_PMD_SIZE;
+	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
+
+	spin_lock(ptl);
+	if (page)
+		put_user_huge_page(page);
+	if (unlikely(!pmd_same(*pmd, orig_pmd))) {
+		spin_unlock(ptl);
+		mem_cgroup_cancel_charge(new_page, memcg);
+		put_page(new_page);
+		goto out_mn;
+	} else {
+		pmd_t entry;
+		entry = mk_huge_pmd(new_page, vma->vm_page_prot);
+		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
+		pmdp_clear_flush_notify(vma, haddr, pmd);
+		page_add_new_anon_rmap(new_page, vma, haddr);
+		mem_cgroup_commit_charge(new_page, memcg, false);
+		lru_cache_add_active_or_unevictable(new_page, vma);
+		set_pmd_at(mm, haddr, pmd, entry);
+		update_mmu_cache_pmd(vma, address, pmd);
+		if (!page) {
+			add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
+			put_huge_zero_page();
+		} else {
+			VM_BUG_ON_PAGE(!PageHead(page), page);
+			page_remove_rmap(page);
+			put_page(page);
+		}
+		ret |= VM_FAULT_WRITE;
+	}
+	spin_unlock(ptl);
+out_mn:
+	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
+out:
+	return ret;
+out_unlock:
+	spin_unlock(ptl);
+	return ret;
+}
+
+struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
+				   unsigned long addr,
+				   pmd_t *pmd,
+				   unsigned int flags)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	struct page *page = NULL;
+
+	assert_spin_locked(pmd_lockptr(mm, pmd));
+
+	if (flags & FOLL_WRITE && !pmd_write(*pmd))
+		goto out;
+
+	/* Avoid dumping huge zero page */
+	if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd))
+		return ERR_PTR(-EFAULT);
+
+	/* Full NUMA hinting faults to serialise migration in fault paths */
+	if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
+		goto out;
+
+	page = pmd_page(*pmd);
+	VM_BUG_ON_PAGE(!PageHead(page), 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));
+		if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
+					  pmd, _pmd,  1))
+			update_mmu_cache_pmd(vma, addr, pmd);
+	}
+	if ((flags & FOLL_POPULATE) && (vma->vm_flags & VM_LOCKED)) {
+		if (page->mapping && trylock_page(page)) {
+			lru_add_drain();
+			if (page->mapping)
+				mlock_vma_page(page);
+			unlock_page(page);
+		}
+	}
+	page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
+	VM_BUG_ON_PAGE(!PageCompound(page), page);
+	if (flags & FOLL_GET)
+		get_page_foll(page);
+
+out:
+	return page;
+}
+
+/* NUMA hinting page fault entry point for trans huge pmds */
+int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
+				unsigned long addr, pmd_t pmd, pmd_t *pmdp)
+{
+	spinlock_t *ptl;
+	struct anon_vma *anon_vma = NULL;
+	struct page *page;
+	unsigned long haddr = addr & HPAGE_PMD_MASK;
+	int page_nid = -1, this_nid = numa_node_id();
+	int target_nid, last_cpupid = -1;
+	bool page_locked;
+	bool migrated = false;
+	bool was_writable;
+	int flags = 0;
+
+	/* A PROT_NONE fault should not end up here */
+	BUG_ON(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)));
+
+	ptl = pmd_lock(mm, pmdp);
+	if (unlikely(!pmd_same(pmd, *pmdp)))
+		goto out_unlock;
+
+	/*
+	 * If there are potential migrations, wait for completion and retry
+	 * without disrupting NUMA hinting information. Do not relock and
+	 * check_same as the page may no longer be mapped.
+	 */
+	if (unlikely(pmd_trans_migrating(*pmdp))) {
+		page = pmd_page(*pmdp);
+		spin_unlock(ptl);
+		wait_on_page_locked(page);
+		goto out;
+	}
+
+	page = pmd_page(pmd);
+	BUG_ON(is_huge_zero_page(page));
+	page_nid = page_to_nid(page);
+	last_cpupid = page_cpupid_last(page);
+	count_vm_numa_event(NUMA_HINT_FAULTS);
+	if (page_nid == this_nid) {
+		count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
+		flags |= TNF_FAULT_LOCAL;
+	}
+
+	/* See similar comment in do_numa_page for explanation */
+	if (!(vma->vm_flags & VM_WRITE))
+		flags |= TNF_NO_GROUP;
+
+	/*
+	 * Acquire the page lock to serialise THP migrations but avoid dropping
+	 * page_table_lock if at all possible
+	 */
+	page_locked = trylock_page(page);
+	target_nid = mpol_misplaced(page, vma, haddr);
+	if (target_nid == -1) {
+		/* If the page was locked, there are no parallel migrations */
+		if (page_locked)
+			goto clear_pmdnuma;
+	}
+
+	/* Migration could have started since the pmd_trans_migrating check */
+	if (!page_locked) {
+		spin_unlock(ptl);
+		wait_on_page_locked(page);
+		page_nid = -1;
+		goto out;
+	}
+
+	/*
+	 * Page is misplaced. Page lock serialises migrations. Acquire anon_vma
+	 * to serialises splits
+	 */
+	get_page(page);
+	spin_unlock(ptl);
+	anon_vma = page_lock_anon_vma_read(page);
+
+	/* Confirm the PMD did not change while page_table_lock was released */
+	spin_lock(ptl);
+	if (unlikely(!pmd_same(pmd, *pmdp))) {
+		unlock_page(page);
+		put_page(page);
+		page_nid = -1;
+		goto out_unlock;
+	}
+
+	/* Bail if we fail to protect against THP splits for any reason */
+	if (unlikely(!anon_vma)) {
+		put_page(page);
+		page_nid = -1;
+		goto clear_pmdnuma;
+	}
+
+	/*
+	 * Migrate the THP to the requested node, returns with page unlocked
+	 * and access rights restored.
+	 */
+	spin_unlock(ptl);
+	migrated = migrate_misplaced_transhuge_page(mm, vma,
+				pmdp, pmd, addr, page, target_nid);
+	if (migrated) {
+		flags |= TNF_MIGRATED;
+		page_nid = target_nid;
+	} else
+		flags |= TNF_MIGRATE_FAIL;
+
+	goto out;
+clear_pmdnuma:
+	BUG_ON(!PageLocked(page));
+	was_writable = pmd_write(pmd);
+	pmd = pmd_modify(pmd, vma->vm_page_prot);
+	pmd = pmd_mkyoung(pmd);
+	if (was_writable)
+		pmd = pmd_mkwrite(pmd);
+	set_pmd_at(mm, haddr, pmdp, pmd);
+	update_mmu_cache_pmd(vma, addr, pmdp);
+	unlock_page(page);
+out_unlock:
+	spin_unlock(ptl);
+
+out:
+	if (anon_vma)
+		page_unlock_anon_vma_read(anon_vma);
+
+	if (page_nid != -1)
+		task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR, flags);
+
+	return 0;
+}
+
+int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
+		 pmd_t *pmd, unsigned long addr)
+{
+	spinlock_t *ptl;
+	int ret = 0;
+
+	if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
+		struct page *page;
+		pgtable_t pgtable;
+		pmd_t orig_pmd;
+		/*
+		 * For architectures like ppc64 we look at deposited pgtable
+		 * when calling pmdp_get_and_clear. So do the
+		 * pgtable_trans_huge_withdraw after finishing pmdp related
+		 * operations.
+		 */
+		orig_pmd = pmdp_get_and_clear_full(tlb->mm, addr, pmd,
+						   tlb->fullmm);
+		tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
+		pgtable = pgtable_trans_huge_withdraw(tlb->mm, pmd);
+		if (is_huge_zero_pmd(orig_pmd)) {
+			atomic_long_dec(&tlb->mm->nr_ptes);
+			spin_unlock(ptl);
+			put_huge_zero_page();
+		} else {
+			page = pmd_page(orig_pmd);
+			page_remove_rmap(page);
+			VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
+			add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
+			VM_BUG_ON_PAGE(!PageHead(page), page);
+			atomic_long_dec(&tlb->mm->nr_ptes);
+			spin_unlock(ptl);
+			tlb_remove_page(tlb, page);
+		}
+		pte_free(tlb->mm, pgtable);
+		ret = 1;
+	}
+	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)
+{
+	spinlock_t *old_ptl, *new_ptl;
+	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;
+	}
+
+	/*
+	 * We don't have to worry about the ordering of src and dst
+	 * ptlocks because exclusive mmap_sem prevents deadlock.
+	 */
+	ret = __pmd_trans_huge_lock(old_pmd, vma, &old_ptl);
+	if (ret == 1) {
+		new_ptl = pmd_lockptr(mm, new_pmd);
+		if (new_ptl != old_ptl)
+			spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
+		pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
+		VM_BUG_ON(!pmd_none(*new_pmd));
+
+		if (pmd_move_must_withdraw(new_ptl, old_ptl)) {
+			pgtable_t pgtable;
+			pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
+			pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
+		}
+		set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
+		if (new_ptl != old_ptl)
+			spin_unlock(new_ptl);
+		spin_unlock(old_ptl);
+	}
+out:
+	return ret;
+}
+
+/*
+ * Returns
+ *  - 0 if PMD could not be locked
+ *  - 1 if PMD was locked but protections unchange and TLB flush unnecessary
+ *  - HPAGE_PMD_NR is protections changed and TLB flush necessary
+ */
+int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
+		unsigned long addr, pgprot_t newprot, int prot_numa)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	spinlock_t *ptl;
+	int ret = 0;
+
+	if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
+		pmd_t entry;
+		bool preserve_write = prot_numa && pmd_write(*pmd);
+		ret = 1;
+
+		/*
+		 * Avoid trapping faults against the zero page. The read-only
+		 * data is likely to be read-cached on the local CPU and
+		 * local/remote hits to the zero page are not interesting.
+		 */
+		if (prot_numa && is_huge_zero_pmd(*pmd)) {
+			spin_unlock(ptl);
+			return ret;
+		}
+
+		if (!prot_numa || !pmd_protnone(*pmd)) {
+			entry = pmdp_get_and_clear_notify(mm, addr, pmd);
+			entry = pmd_modify(entry, newprot);
+			if (preserve_write)
+				entry = pmd_mkwrite(entry);
+			ret = HPAGE_PMD_NR;
+			set_pmd_at(mm, addr, pmd, entry);
+			BUG_ON(!preserve_write && pmd_write(entry));
+		}
+		spin_unlock(ptl);
+	}
+
+	return ret;
+}
+
+/*
+ * Returns 1 if a given pmd maps a stable (not under splitting) thp.
+ * Returns -1 if it maps a thp under splitting. Returns 0 otherwise.
+ *
+ * Note that if it returns 1, this routine returns without unlocking page
+ * table locks. So callers must unlock them.
+ */
+int __pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma,
+		spinlock_t **ptl)
+{
+	*ptl = pmd_lock(vma->vm_mm, pmd);
+	if (likely(pmd_trans_huge(*pmd))) {
+		if (unlikely(pmd_trans_splitting(*pmd))) {
+			spin_unlock(*ptl);
+			wait_split_huge_page(vma->anon_vma, pmd);
+			return -1;
+		} else {
+			/* Thp mapped by 'pmd' is stable, so we can
+			 * handle it as it is. */
+			return 1;
+		}
+	}
+	spin_unlock(*ptl);
+	return 0;
+}
+
+/*
+ * This function returns whether a given @page is mapped onto the @address
+ * in the virtual space of @mm.
+ *
+ * When it's true, this function returns *pmd with holding the page table lock
+ * and passing it back to the caller via @ptl.
+ * If it's false, returns NULL without holding the page table lock.
+ */
+pmd_t *page_check_address_pmd(struct page *page,
+			      struct mm_struct *mm,
+			      unsigned long address,
+			      enum page_check_address_pmd_flag flag,
+			      spinlock_t **ptl)
+{
+	pgd_t *pgd;
+	pud_t *pud;
+	pmd_t *pmd;
+
+	if (address & ~HPAGE_PMD_MASK)
+		return NULL;
+
+	pgd = pgd_offset(mm, address);
+	if (!pgd_present(*pgd))
+		return NULL;
+	pud = pud_offset(pgd, address);
+	if (!pud_present(*pud))
+		return NULL;
+	pmd = pmd_offset(pud, address);
+
+	*ptl = pmd_lock(mm, pmd);
+	if (!pmd_present(*pmd))
+		goto unlock;
+	if (pmd_page(*pmd) != page)
+		goto unlock;
+	/*
+	 * 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 unlock;
+	if (pmd_trans_huge(*pmd)) {
+		VM_BUG_ON(flag == PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG &&
+			  !pmd_trans_splitting(*pmd));
+		return pmd;
+	}
+unlock:
+	spin_unlock(*ptl);
+	return NULL;
+}
+
+static int __split_huge_page_splitting(struct page *page,
+				       struct vm_area_struct *vma,
+				       unsigned long address)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	spinlock_t *ptl;
+	pmd_t *pmd;
+	int ret = 0;
+	/* For mmu_notifiers */
+	const unsigned long mmun_start = address;
+	const unsigned long mmun_end   = address + HPAGE_PMD_SIZE;
+
+	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
+	pmd = page_check_address_pmd(page, mm, address,
+			PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG, &ptl);
+	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->rwsem to
+		 * serialize against split_huge_page*.
+		 */
+		pmdp_splitting_flush(vma, address, pmd);
+
+		ret = 1;
+		spin_unlock(ptl);
+	}
+	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
+
+	return ret;
+}
+
+static void __split_huge_page_refcount(struct page *page,
+				       struct list_head *list)
+{
+	int i;
+	struct zone *zone = page_zone(page);
+	struct lruvec *lruvec;
+	int tail_count = 0;
+
+	/* prevent PageLRU to go away from under us, and freeze lru stats */
+	spin_lock_irq(&zone->lru_lock);
+	lruvec = mem_cgroup_page_lruvec(page, zone);
+
+	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__after_atomic();
+
+		/*
+		 * 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) |
+				      (1L << PG_active) |
+				      (1L << PG_unevictable)));
+		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;
+		page_cpupid_xchg_last(page_tail, page_cpupid_last(page));
+
+		BUG_ON(!PageAnon(page_tail));
+		BUG_ON(!PageUptodate(page_tail));
+		BUG_ON(!PageDirty(page_tail));
+		BUG_ON(!PageSwapBacked(page_tail));
+
+		lru_add_page_tail(page, page_tail, lruvec, list);
+	}
+	atomic_sub(tail_count, &page->_count);
+	BUG_ON(atomic_read(&page->_count) <= 0);
+
+	__mod_zone_page_state(zone, NR_ANON_TRANSPARENT_HUGEPAGES, -1);
+
+	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;
+	spinlock_t *ptl;
+	pmd_t *pmd, _pmd;
+	int ret = 0, i;
+	pgtable_t pgtable;
+	unsigned long haddr;
+
+	pmd = page_check_address_pmd(page, mm, address,
+			PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG, &ptl);
+	if (pmd) {
+		pgtable = pgtable_trans_huge_withdraw(mm, pmd);
+		pmd_populate(mm, &_pmd, pgtable);
+		if (pmd_write(*pmd))
+			BUG_ON(page_mapcount(page) != 1);
+
+		haddr = address;
+		for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
+			pte_t *pte, entry;
+			BUG_ON(PageCompound(page+i));
+			/*
+			 * Note that NUMA hinting access restrictions are not
+			 * transferred to avoid any possibility of altering
+			 * permissions across VMAs.
+			 */
+			entry = mk_pte(page + i, vma->vm_page_prot);
+			entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+			if (!pmd_write(*pmd))
+				entry = pte_wrprotect(entry);
+			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);
+		}
+
+		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.
+		 */
+		pmdp_invalidate(vma, address, pmd);
+		pmd_populate(mm, pmd, pgtable);
+		ret = 1;
+		spin_unlock(ptl);
+	}
+
+	return ret;
+}
+
+/* must be called with anon_vma->root->rwsem held */
+static void __split_huge_page(struct page *page,
+			      struct anon_vma *anon_vma,
+			      struct list_head *list)
+{
+	int mapcount, mapcount2;
+	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
+	struct anon_vma_chain *avc;
+
+	BUG_ON(!PageHead(page));
+	BUG_ON(PageTail(page));
+
+	mapcount = 0;
+	anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
+		struct vm_area_struct *vma = avc->vma;
+		unsigned long addr = vma_address(page, vma);
+		BUG_ON(is_vma_temporary_stack(vma));
+		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)) {
+		pr_err("mapcount %d page_mapcount %d\n",
+			mapcount, page_mapcount(page));
+		BUG();
+	}
+
+	__split_huge_page_refcount(page, list);
+
+	mapcount2 = 0;
+	anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
+		struct vm_area_struct *vma = avc->vma;
+		unsigned long addr = vma_address(page, vma);
+		BUG_ON(is_vma_temporary_stack(vma));
+		mapcount2 += __split_huge_page_map(page, vma, addr);
+	}
+	if (mapcount != mapcount2) {
+		pr_err("mapcount %d mapcount2 %d page_mapcount %d\n",
+			mapcount, mapcount2, page_mapcount(page));
+		BUG();
+	}
+}
+
+/*
+ * Split a hugepage into normal pages. This doesn't change the position of head
+ * page. If @list is null, tail pages will be added to LRU list, otherwise, to
+ * @list. Both head page and tail pages will inherit mapping, flags, and so on
+ * from the hugepage.
+ * Return 0 if the hugepage is split successfully otherwise return 1.
+ */
+int split_huge_page_to_list(struct page *page, struct list_head *list)
+{
+	struct anon_vma *anon_vma;
+	int ret = 1;
+
+	BUG_ON(is_huge_zero_page(page));
+	BUG_ON(!PageAnon(page));
+
+	/*
+	 * The caller does not necessarily hold an mmap_sem that would prevent
+	 * the anon_vma disappearing so we first we take a reference to it
+	 * and then lock the anon_vma for write. This is similar to
+	 * page_lock_anon_vma_read except the write lock is taken to serialise
+	 * against parallel split or collapse operations.
+	 */
+	anon_vma = page_get_anon_vma(page);
+	if (!anon_vma)
+		goto out;
+	anon_vma_lock_write(anon_vma);
+
+	ret = 0;
+	if (!PageCompound(page))
+		goto out_unlock;
+
+	BUG_ON(!PageSwapBacked(page));
+	__split_huge_page(page, anon_vma, list);
+	count_vm_event(THP_SPLIT);
+
+	BUG_ON(PageCompound(page));
+out_unlock:
+	anon_vma_unlock_write(anon_vma);
+	put_anon_vma(anon_vma);
+out:
+	return ret;
+}
+
+#define VM_NO_THP (VM_SPECIAL | 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:
+#ifdef CONFIG_S390
+		/*
+		 * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
+		 * can't handle this properly after s390_enable_sie, so we simply
+		 * ignore the madvise to prevent qemu from causing a SIGSEGV.
+		 */
+		if (mm_has_pgste(vma->vm_mm))
+			return 0;
+#endif
+		/*
+		 * 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, *vm_flags)))
+			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_exit(void)
+{
+	kmem_cache_destroy(mm_slot_cache);
+}
+
+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 struct mm_slot *get_mm_slot(struct mm_struct *mm)
+{
+	struct mm_slot *mm_slot;
+
+	hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
+		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)
+{
+	mm_slot->mm = mm;
+	hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
+}
+
+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_MM(khugepaged_test_exit(mm), 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 vm_flags)
+{
+	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;
+	VM_BUG_ON_VMA(vm_flags & VM_NO_THP, vma);
+	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
+	hend = vma->vm_end & HPAGE_PMD_MASK;
+	if (hstart < hend)
+		return khugepaged_enter(vma, vm_flags);
+	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) {
+		hash_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) && !is_zero_pfn(pte_pfn(pteval)))
+			release_pte_page(pte_page(pteval));
+	}
+}
+
+static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
+					unsigned long address,
+					pte_t *pte)
+{
+	struct page *page;
+	pte_t *_pte;
+	int none_or_zero = 0;
+	bool referenced = false, writable = false;
+	for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
+	     _pte++, address += PAGE_SIZE) {
+		pte_t pteval = *_pte;
+		if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
+			if (++none_or_zero <= khugepaged_max_ptes_none)
+				continue;
+			else
+				goto out;
+		}
+		if (!pte_present(pteval))
+			goto out;
+		page = vm_normal_page(vma, address, pteval);
+		if (unlikely(!page))
+			goto out;
+
+		VM_BUG_ON_PAGE(PageCompound(page), page);
+		VM_BUG_ON_PAGE(!PageAnon(page), page);
+		VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
+
+		/*
+		 * 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))
+			goto out;
+
+		/*
+		 * cannot use mapcount: can't collapse if there's a gup pin.
+		 * The page must only be referenced by the scanned process
+		 * and page swap cache.
+		 */
+		if (page_count(page) != 1 + !!PageSwapCache(page)) {
+			unlock_page(page);
+			goto out;
+		}
+		if (pte_write(pteval)) {
+			writable = true;
+		} else {
+			if (PageSwapCache(page) && !reuse_swap_page(page)) {
+				unlock_page(page);
+				goto out;
+			}
+			/*
+			 * Page is not in the swap cache. It can be collapsed
+			 * into a THP.
+			 */
+		}
+
+		/*
+		 * Isolate the page to avoid collapsing an hugepage
+		 * currently in use by the VM.
+		 */
+		if (isolate_lru_page(page)) {
+			unlock_page(page);
+			goto out;
+		}
+		/* 0 stands for page_is_file_cache(page) == false */
+		inc_zone_page_state(page, NR_ISOLATED_ANON + 0);
+		VM_BUG_ON_PAGE(!PageLocked(page), page);
+		VM_BUG_ON_PAGE(PageLRU(page), 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 = true;
+	}
+	if (likely(referenced && writable))
+		return 1;
+out:
+	release_pte_pages(pte, _pte);
+	return 0;
+}
+
+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) || is_zero_pfn(pte_pfn(pteval))) {
+			clear_user_highpage(page, address);
+			add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
+			if (is_zero_pfn(pte_pfn(pteval))) {
+				/*
+				 * ptl mostly unnecessary.
+				 */
+				spin_lock(ptl);
+				/*
+				 * paravirt calls inside pte_clear here are
+				 * superfluous.
+				 */
+				pte_clear(vma->vm_mm, address, _pte);
+				spin_unlock(ptl);
+			}
+		} else {
+			src_page = pte_page(pteval);
+			copy_user_highpage(page, src_page, address, vma);
+			VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page);
+			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 khugepaged_alloc_sleep(void)
+{
+	wait_event_freezable_timeout(khugepaged_wait, false,
+			msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
+}
+
+static int khugepaged_node_load[MAX_NUMNODES];
+
+static bool khugepaged_scan_abort(int nid)
+{
+	int i;
+
+	/*
+	 * If zone_reclaim_mode is disabled, then no extra effort is made to
+	 * allocate memory locally.
+	 */
+	if (!zone_reclaim_mode)
+		return false;
+
+	/* If there is a count for this node already, it must be acceptable */
+	if (khugepaged_node_load[nid])
+		return false;
+
+	for (i = 0; i < MAX_NUMNODES; i++) {
+		if (!khugepaged_node_load[i])
+			continue;
+		if (node_distance(nid, i) > RECLAIM_DISTANCE)
+			return true;
+	}
+	return false;
+}
+
+#ifdef CONFIG_NUMA
+static int khugepaged_find_target_node(void)
+{
+	static int last_khugepaged_target_node = NUMA_NO_NODE;
+	int nid, target_node = 0, max_value = 0;
+
+	/* find first node with max normal pages hit */
+	for (nid = 0; nid < MAX_NUMNODES; nid++)
+		if (khugepaged_node_load[nid] > max_value) {
+			max_value = khugepaged_node_load[nid];
+			target_node = nid;
+		}
+
+	/* do some balance if several nodes have the same hit record */
+	if (target_node <= last_khugepaged_target_node)
+		for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
+				nid++)
+			if (max_value == khugepaged_node_load[nid]) {
+				target_node = nid;
+				break;
+			}
+
+	last_khugepaged_target_node = target_node;
+	return target_node;
+}
+
+static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
+{
+	if (IS_ERR(*hpage)) {
+		if (!*wait)
+			return false;
+
+		*wait = false;
+		*hpage = NULL;
+		khugepaged_alloc_sleep();
+	} else if (*hpage) {
+		put_page(*hpage);
+		*hpage = NULL;
+	}
+
+	return true;
+}
+
+static struct page *
+khugepaged_alloc_page(struct page **hpage, gfp_t gfp, struct mm_struct *mm,
+		       struct vm_area_struct *vma, unsigned long address,
+		       int node)
+{
+	VM_BUG_ON_PAGE(*hpage, *hpage);
+
+	/*
+	 * Before allocating the hugepage, release the mmap_sem read lock.
+	 * The allocation can take potentially a long time if it involves
+	 * sync compaction, and we do not need to hold the mmap_sem during
+	 * that. We will recheck the vma after taking it again in write mode.
+	 */
+	up_read(&mm->mmap_sem);
+
+	*hpage = alloc_pages_exact_node(node, gfp, HPAGE_PMD_ORDER);
+	if (unlikely(!*hpage)) {
+		count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
+		*hpage = ERR_PTR(-ENOMEM);
+		return NULL;
+	}
+
+	count_vm_event(THP_COLLAPSE_ALLOC);
+	return *hpage;
+}
+#else
+static int khugepaged_find_target_node(void)
+{
+	return 0;
+}
+
+static inline struct page *alloc_hugepage(int defrag)
+{
+	return alloc_pages(alloc_hugepage_gfpmask(defrag, 0),
+			   HPAGE_PMD_ORDER);
+}
+
+static struct page *khugepaged_alloc_hugepage(bool *wait)
+{
+	struct page *hpage;
+
+	do {
+		hpage = alloc_hugepage(khugepaged_defrag());
+		if (!hpage) {
+			count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
+			if (!*wait)
+				return NULL;
+
+			*wait = false;
+			khugepaged_alloc_sleep();
+		} else
+			count_vm_event(THP_COLLAPSE_ALLOC);
+	} while (unlikely(!hpage) && likely(khugepaged_enabled()));
+
+	return hpage;
+}
+
+static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
+{
+	if (!*hpage)
+		*hpage = khugepaged_alloc_hugepage(wait);
+
+	if (unlikely(!*hpage))
+		return false;
+
+	return true;
+}
+
+static struct page *
+khugepaged_alloc_page(struct page **hpage, gfp_t gfp, struct mm_struct *mm,
+		       struct vm_area_struct *vma, unsigned long address,
+		       int node)
+{
+	up_read(&mm->mmap_sem);
+	VM_BUG_ON(!*hpage);
+
+	return  *hpage;
+}
+#endif
+
+static bool hugepage_vma_check(struct vm_area_struct *vma)
+{
+	if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
+	    (vma->vm_flags & VM_NOHUGEPAGE))
+		return false;
+
+	if (!vma->anon_vma || vma->vm_ops)
+		return false;
+	if (is_vma_temporary_stack(vma))
+		return false;
+	VM_BUG_ON_VMA(vma->vm_flags & VM_NO_THP, vma);
+	return true;
+}
+
+static void collapse_huge_page(struct mm_struct *mm,
+				   unsigned long address,
+				   struct page **hpage,
+				   struct vm_area_struct *vma,
+				   int node)
+{
+	pmd_t *pmd, _pmd;
+	pte_t *pte;
+	pgtable_t pgtable;
+	struct page *new_page;
+	spinlock_t *pmd_ptl, *pte_ptl;
+	int isolated;
+	unsigned long hstart, hend;
+	struct mem_cgroup *memcg;
+	unsigned long mmun_start;	/* For mmu_notifiers */
+	unsigned long mmun_end;		/* For mmu_notifiers */
+	gfp_t gfp;
+
+	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
+
+	/* Only allocate from the target node */
+	gfp = alloc_hugepage_gfpmask(khugepaged_defrag(), __GFP_OTHER_NODE) |
+		__GFP_THISNODE;
+
+	/* release the mmap_sem read lock. */
+	new_page = khugepaged_alloc_page(hpage, gfp, mm, vma, address, node);
+	if (!new_page)
+		return;
+
+	if (unlikely(mem_cgroup_try_charge(new_page, mm,
+					   gfp, &memcg)))
+		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);
+	if (!vma)
+		goto out;
+	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 (!hugepage_vma_check(vma))
+		goto out;
+	pmd = mm_find_pmd(mm, address);
+	if (!pmd)
+		goto out;
+
+	anon_vma_lock_write(vma->anon_vma);
+
+	pte = pte_offset_map(pmd, address);
+	pte_ptl = pte_lockptr(mm, pmd);
+
+	mmun_start = address;
+	mmun_end   = address + HPAGE_PMD_SIZE;
+	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
+	pmd_ptl = pmd_lock(mm, pmd); /* 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(vma, address, pmd);
+	spin_unlock(pmd_ptl);
+	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
+
+	spin_lock(pte_ptl);
+	isolated = __collapse_huge_page_isolate(vma, address, pte);
+	spin_unlock(pte_ptl);
+
+	if (unlikely(!isolated)) {
+		pte_unmap(pte);
+		spin_lock(pmd_ptl);
+		BUG_ON(!pmd_none(*pmd));
+		/*
+		 * We can only use set_pmd_at when establishing
+		 * hugepmds and never for establishing regular pmds that
+		 * points to regular pagetables. Use pmd_populate for that
+		 */
+		pmd_populate(mm, pmd, pmd_pgtable(_pmd));
+		spin_unlock(pmd_ptl);
+		anon_vma_unlock_write(vma->anon_vma);
+		goto out;
+	}
+
+	/*
+	 * All pages are isolated and locked so anon_vma rmap
+	 * can't run anymore.
+	 */
+	anon_vma_unlock_write(vma->anon_vma);
+
+	__collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
+	pte_unmap(pte);
+	__SetPageUptodate(new_page);
+	pgtable = pmd_pgtable(_pmd);
+
+	_pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
+	_pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
+
+	/*
+	 * 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(pmd_ptl);
+	BUG_ON(!pmd_none(*pmd));
+	page_add_new_anon_rmap(new_page, vma, address);
+	mem_cgroup_commit_charge(new_page, memcg, false);
+	lru_cache_add_active_or_unevictable(new_page, vma);
+	pgtable_trans_huge_deposit(mm, pmd, pgtable);
+	set_pmd_at(mm, address, pmd, _pmd);
+	update_mmu_cache_pmd(vma, address, pmd);
+	spin_unlock(pmd_ptl);
+
+	*hpage = NULL;
+
+	khugepaged_pages_collapsed++;
+out_up_write:
+	up_write(&mm->mmap_sem);
+	return;
+
+out:
+	mem_cgroup_cancel_charge(new_page, memcg);
+	goto out_up_write;
+}
+
+static int khugepaged_scan_pmd(struct mm_struct *mm,
+			       struct vm_area_struct *vma,
+			       unsigned long address,
+			       struct page **hpage)
+{
+	pmd_t *pmd;
+	pte_t *pte, *_pte;
+	int ret = 0, none_or_zero = 0;
+	struct page *page;
+	unsigned long _address;
+	spinlock_t *ptl;
+	int node = NUMA_NO_NODE;
+	bool writable = false, referenced = false;
+
+	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
+
+	pmd = mm_find_pmd(mm, address);
+	if (!pmd)
+		goto out;
+
+	memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
+	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) || is_zero_pfn(pte_pfn(pteval))) {
+			if (++none_or_zero <= khugepaged_max_ptes_none)
+				continue;
+			else
+				goto out_unmap;
+		}
+		if (!pte_present(pteval))
+			goto out_unmap;
+		if (pte_write(pteval))
+			writable = true;
+
+		page = vm_normal_page(vma, _address, pteval);
+		if (unlikely(!page))
+			goto out_unmap;
+		/*
+		 * Record which node the original page is from and save this
+		 * information to khugepaged_node_load[].
+		 * Khupaged will allocate hugepage from the node has the max
+		 * hit record.
+		 */
+		node = page_to_nid(page);
+		if (khugepaged_scan_abort(node))
+			goto out_unmap;
+		khugepaged_node_load[node]++;
+		VM_BUG_ON_PAGE(PageCompound(page), page);
+		if (!PageLRU(page) || PageLocked(page) || !PageAnon(page))
+			goto out_unmap;
+		/*
+		 * cannot use mapcount: can't collapse if there's a gup pin.
+		 * The page must only be referenced by the scanned process
+		 * and page swap cache.
+		 */
+		if (page_count(page) != 1 + !!PageSwapCache(page))
+			goto out_unmap;
+		if (pte_young(pteval) || PageReferenced(page) ||
+		    mmu_notifier_test_young(vma->vm_mm, address))
+			referenced = true;
+	}
+	if (referenced && writable)
+		ret = 1;
+out_unmap:
+	pte_unmap_unlock(pte, ptl);
+	if (ret) {
+		node = khugepaged_find_target_node();
+		/* 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(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
+
+	if (khugepaged_test_exit(mm)) {
+		/* free mm_slot */
+		hash_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(NR_CPUS != 1 && !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 (!hugepage_vma_check(vma)) {
+skip:
+			progress++;
+			continue;
+		}
+		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) ||
+		kthread_should_stop();
+}
+
+static void khugepaged_do_scan(void)
+{
+	struct page *hpage = NULL;
+	unsigned int progress = 0, pass_through_head = 0;
+	unsigned int pages = khugepaged_pages_to_scan;
+	bool wait = true;
+
+	barrier(); /* write khugepaged_pages_to_scan to local stack */
+
+	while (progress < pages) {
+		if (!khugepaged_prealloc_page(&hpage, &wait))
+			break;
+
+		cond_resched();
+
+		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);
+	}
+
+	if (!IS_ERR_OR_NULL(hpage))
+		put_page(hpage);
+}
+
+static void khugepaged_wait_work(void)
+{
+	try_to_freeze();
+
+	if (khugepaged_has_work()) {
+		if (!khugepaged_scan_sleep_millisecs)
+			return;
+
+		wait_event_freezable_timeout(khugepaged_wait,
+					     kthread_should_stop(),
+			msecs_to_jiffies(khugepaged_scan_sleep_millisecs));
+		return;
+	}
+
+	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, MAX_NICE);
+
+	while (!kthread_should_stop()) {
+		khugepaged_do_scan();
+		khugepaged_wait_work();
+	}
+
+	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);
+	return 0;
+}
+
+static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
+		unsigned long haddr, pmd_t *pmd)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	pgtable_t pgtable;
+	pmd_t _pmd;
+	int i;
+
+	pmdp_clear_flush_notify(vma, haddr, pmd);
+	/* leave pmd empty until pte is filled */
+
+	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
+	pmd_populate(mm, &_pmd, pgtable);
+
+	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
+		pte_t *pte, entry;
+		entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
+		entry = pte_mkspecial(entry);
+		pte = pte_offset_map(&_pmd, haddr);
+		VM_BUG_ON(!pte_none(*pte));
+		set_pte_at(mm, haddr, pte, entry);
+		pte_unmap(pte);
+	}
+	smp_wmb(); /* make pte visible before pmd */
+	pmd_populate(mm, pmd, pgtable);
+	put_huge_zero_page();
+}
+
+void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
+		pmd_t *pmd)
+{
+	spinlock_t *ptl;
+	struct page *page;
+	struct mm_struct *mm = vma->vm_mm;
+	unsigned long haddr = address & HPAGE_PMD_MASK;
+	unsigned long mmun_start;	/* For mmu_notifiers */
+	unsigned long mmun_end;		/* For mmu_notifiers */
+
+	BUG_ON(vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE);
+
+	mmun_start = haddr;
+	mmun_end   = haddr + HPAGE_PMD_SIZE;
+again:
+	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
+	ptl = pmd_lock(mm, pmd);
+	if (unlikely(!pmd_trans_huge(*pmd))) {
+		spin_unlock(ptl);
+		mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
+		return;
+	}
+	if (is_huge_zero_pmd(*pmd)) {
+		__split_huge_zero_page_pmd(vma, haddr, pmd);
+		spin_unlock(ptl);
+		mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
+		return;
+	}
+	page = pmd_page(*pmd);
+	VM_BUG_ON_PAGE(!page_count(page), page);
+	get_page(page);
+	spin_unlock(ptl);
+	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
+
+	split_huge_page(page);
+
+	put_page(page);
+
+	/*
+	 * We don't always have down_write of mmap_sem here: a racing
+	 * do_huge_pmd_wp_page() might have copied-on-write to another
+	 * huge page before our split_huge_page() got the anon_vma lock.
+	 */
+	if (unlikely(pmd_trans_huge(*pmd)))
+		goto again;
+}
+
+void split_huge_page_pmd_mm(struct mm_struct *mm, unsigned long address,
+		pmd_t *pmd)
+{
+	struct vm_area_struct *vma;
+
+	vma = find_vma(mm, address);
+	BUG_ON(vma == NULL);
+	split_huge_page_pmd(vma, address, 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(mm, address, 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);
+	}
+}