Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3021 insertions, 0 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
new file mode 100644
index 000000000..76f8dedc0
--- /dev/null
+++ b/mm/migrate.c
@@ -0,0 +1,3021 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Memory Migration functionality - linux/mm/migrate.c
+ *
+ * Copyright (C) 2006 Silicon Graphics, Inc., Christoph Lameter
+ *
+ * Page migration was first developed in the context of the memory hotplug
+ * project. The main authors of the migration code are:
+ *
+ * IWAMOTO Toshihiro <iwamoto@valinux.co.jp>
+ * Hirokazu Takahashi <taka@valinux.co.jp>
+ * Dave Hansen <haveblue@us.ibm.com>
+ * Christoph Lameter
+ */
+
+#include <linux/migrate.h>
+#include <linux/export.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
+#include <linux/pagemap.h>
+#include <linux/buffer_head.h>
+#include <linux/mm_inline.h>
+#include <linux/nsproxy.h>
+#include <linux/pagevec.h>
+#include <linux/ksm.h>
+#include <linux/rmap.h>
+#include <linux/topology.h>
+#include <linux/cpu.h>
+#include <linux/cpuset.h>
+#include <linux/writeback.h>
+#include <linux/mempolicy.h>
+#include <linux/vmalloc.h>
+#include <linux/security.h>
+#include <linux/backing-dev.h>
+#include <linux/compaction.h>
+#include <linux/syscalls.h>
+#include <linux/compat.h>
+#include <linux/hugetlb.h>
+#include <linux/hugetlb_cgroup.h>
+#include <linux/gfp.h>
+#include <linux/pfn_t.h>
+#include <linux/memremap.h>
+#include <linux/userfaultfd_k.h>
+#include <linux/balloon_compaction.h>
+#include <linux/mmu_notifier.h>
+#include <linux/page_idle.h>
+#include <linux/page_owner.h>
+#include <linux/sched/mm.h>
+#include <linux/ptrace.h>
+
+#include <asm/tlbflush.h>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/migrate.h>
+
+#include "internal.h"
+
+/*
+ * migrate_prep() needs to be called before we start compiling a list of pages
+ * to be migrated using isolate_lru_page(). If scheduling work on other CPUs is
+ * undesirable, use migrate_prep_local()
+ */
+int migrate_prep(void)
+{
+	/*
+	 * Clear the LRU lists so pages can be isolated.
+	 * Note that pages may be moved off the LRU after we have
+	 * drained them. Those pages will fail to migrate like other
+	 * pages that may be busy.
+	 */
+	lru_add_drain_all();
+
+	return 0;
+}
+
+/* Do the necessary work of migrate_prep but not if it involves other CPUs */
+int migrate_prep_local(void)
+{
+	lru_add_drain();
+
+	return 0;
+}
+
+int isolate_movable_page(struct page *page, isolate_mode_t mode)
+{
+	struct address_space *mapping;
+
+	/*
+	 * Avoid burning cycles with pages that are yet under __free_pages(),
+	 * or just got freed under us.
+	 *
+	 * In case we 'win' a race for a movable page being freed under us and
+	 * raise its refcount preventing __free_pages() from doing its job
+	 * the put_page() at the end of this block will take care of
+	 * release this page, thus avoiding a nasty leakage.
+	 */
+	if (unlikely(!get_page_unless_zero(page)))
+		goto out;
+
+	/*
+	 * Check PageMovable before holding a PG_lock because page's owner
+	 * assumes anybody doesn't touch PG_lock of newly allocated page
+	 * so unconditionally grapping the lock ruins page's owner side.
+	 */
+	if (unlikely(!__PageMovable(page)))
+		goto out_putpage;
+	/*
+	 * As movable pages are not isolated from LRU lists, concurrent
+	 * compaction threads can race against page migration functions
+	 * as well as race against the releasing a page.
+	 *
+	 * In order to avoid having an already isolated movable page
+	 * being (wrongly) re-isolated while it is under migration,
+	 * or to avoid attempting to isolate pages being released,
+	 * lets be sure we have the page lock
+	 * before proceeding with the movable page isolation steps.
+	 */
+	if (unlikely(!trylock_page(page)))
+		goto out_putpage;
+
+	if (!PageMovable(page) || PageIsolated(page))
+		goto out_no_isolated;
+
+	mapping = page_mapping(page);
+	VM_BUG_ON_PAGE(!mapping, page);
+
+	if (!mapping->a_ops->isolate_page(page, mode))
+		goto out_no_isolated;
+
+	/* Driver shouldn't use PG_isolated bit of page->flags */
+	WARN_ON_ONCE(PageIsolated(page));
+	__SetPageIsolated(page);
+	unlock_page(page);
+
+	return 0;
+
+out_no_isolated:
+	unlock_page(page);
+out_putpage:
+	put_page(page);
+out:
+	return -EBUSY;
+}
+
+/* It should be called on page which is PG_movable */
+void putback_movable_page(struct page *page)
+{
+	struct address_space *mapping;
+
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE(!PageMovable(page), page);
+	VM_BUG_ON_PAGE(!PageIsolated(page), page);
+
+	mapping = page_mapping(page);
+	mapping->a_ops->putback_page(page);
+	__ClearPageIsolated(page);
+}
+
+/*
+ * Put previously isolated pages back onto the appropriate lists
+ * from where they were once taken off for compaction/migration.
+ *
+ * This function shall be used whenever the isolated pageset has been
+ * built from lru, balloon, hugetlbfs page. See isolate_migratepages_range()
+ * and isolate_huge_page().
+ */
+void putback_movable_pages(struct list_head *l)
+{
+	struct page *page;
+	struct page *page2;
+
+	list_for_each_entry_safe(page, page2, l, lru) {
+		if (unlikely(PageHuge(page))) {
+			putback_active_hugepage(page);
+			continue;
+		}
+		list_del(&page->lru);
+		/*
+		 * We isolated non-lru movable page so here we can use
+		 * __PageMovable because LRU page's mapping cannot have
+		 * PAGE_MAPPING_MOVABLE.
+		 */
+		if (unlikely(__PageMovable(page))) {
+			VM_BUG_ON_PAGE(!PageIsolated(page), page);
+			lock_page(page);
+			if (PageMovable(page))
+				putback_movable_page(page);
+			else
+				__ClearPageIsolated(page);
+			unlock_page(page);
+			put_page(page);
+		} else {
+			mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON +
+					page_is_file_cache(page), -hpage_nr_pages(page));
+			putback_lru_page(page);
+		}
+	}
+}
+
+/*
+ * Restore a potential migration pte to a working pte entry
+ */
+static bool remove_migration_pte(struct page *page, struct vm_area_struct *vma,
+				 unsigned long addr, void *old)
+{
+	struct page_vma_mapped_walk pvmw = {
+		.page = old,
+		.vma = vma,
+		.address = addr,
+		.flags = PVMW_SYNC | PVMW_MIGRATION,
+	};
+	struct page *new;
+	pte_t pte;
+	swp_entry_t entry;
+
+	VM_BUG_ON_PAGE(PageTail(page), page);
+	while (page_vma_mapped_walk(&pvmw)) {
+		if (PageKsm(page))
+			new = page;
+		else
+			new = page - pvmw.page->index +
+				linear_page_index(vma, pvmw.address);
+
+#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
+		/* PMD-mapped THP migration entry */
+		if (!pvmw.pte) {
+			VM_BUG_ON_PAGE(PageHuge(page) || !PageTransCompound(page), page);
+			remove_migration_pmd(&pvmw, new);
+			continue;
+		}
+#endif
+
+		get_page(new);
+		pte = pte_mkold(mk_pte(new, READ_ONCE(vma->vm_page_prot)));
+		if (pte_swp_soft_dirty(*pvmw.pte))
+			pte = pte_mksoft_dirty(pte);
+
+		/*
+		 * Recheck VMA as permissions can change since migration started
+		 */
+		entry = pte_to_swp_entry(*pvmw.pte);
+		if (is_write_migration_entry(entry))
+			pte = maybe_mkwrite(pte, vma);
+
+		if (unlikely(is_zone_device_page(new))) {
+			if (is_device_private_page(new)) {
+				entry = make_device_private_entry(new, pte_write(pte));
+				pte = swp_entry_to_pte(entry);
+			} else if (is_device_public_page(new)) {
+				pte = pte_mkdevmap(pte);
+			}
+		}
+
+#ifdef CONFIG_HUGETLB_PAGE
+		if (PageHuge(new)) {
+			pte = pte_mkhuge(pte);
+			pte = arch_make_huge_pte(pte, vma, new, 0);
+			set_huge_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte);
+			if (PageAnon(new))
+				hugepage_add_anon_rmap(new, vma, pvmw.address);
+			else
+				page_dup_rmap(new, true);
+		} else
+#endif
+		{
+			set_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte);
+
+			if (PageAnon(new))
+				page_add_anon_rmap(new, vma, pvmw.address, false);
+			else
+				page_add_file_rmap(new, false);
+		}
+		if (vma->vm_flags & VM_LOCKED && !PageTransCompound(new))
+			mlock_vma_page(new);
+
+		if (PageTransHuge(page) && PageMlocked(page))
+			clear_page_mlock(page);
+
+		/* No need to invalidate - it was non-present before */
+		update_mmu_cache(vma, pvmw.address, pvmw.pte);
+	}
+
+	return true;
+}
+
+/*
+ * Get rid of all migration entries and replace them by
+ * references to the indicated page.
+ */
+void remove_migration_ptes(struct page *old, struct page *new, bool locked)
+{
+	struct rmap_walk_control rwc = {
+		.rmap_one = remove_migration_pte,
+		.arg = old,
+	};
+
+	if (locked)
+		rmap_walk_locked(new, &rwc);
+	else
+		rmap_walk(new, &rwc);
+}
+
+/*
+ * Something used the pte of a page under migration. We need to
+ * get to the page and wait until migration is finished.
+ * When we return from this function the fault will be retried.
+ */
+void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
+				spinlock_t *ptl)
+{
+	pte_t pte;
+	swp_entry_t entry;
+	struct page *page;
+
+	spin_lock(ptl);
+	pte = *ptep;
+	if (!is_swap_pte(pte))
+		goto out;
+
+	entry = pte_to_swp_entry(pte);
+	if (!is_migration_entry(entry))
+		goto out;
+
+	page = migration_entry_to_page(entry);
+
+	/*
+	 * Once radix-tree replacement of page migration started, page_count
+	 * *must* be zero. And, we don't want to call wait_on_page_locked()
+	 * against a page without get_page().
+	 * So, we use get_page_unless_zero(), here. Even failed, page fault
+	 * will occur again.
+	 */
+	if (!get_page_unless_zero(page))
+		goto out;
+	pte_unmap_unlock(ptep, ptl);
+	wait_on_page_locked(page);
+	put_page(page);
+	return;
+out:
+	pte_unmap_unlock(ptep, ptl);
+}
+
+void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
+				unsigned long address)
+{
+	spinlock_t *ptl = pte_lockptr(mm, pmd);
+	pte_t *ptep = pte_offset_map(pmd, address);
+	__migration_entry_wait(mm, ptep, ptl);
+}
+
+void migration_entry_wait_huge(struct vm_area_struct *vma,
+		struct mm_struct *mm, pte_t *pte)
+{
+	spinlock_t *ptl = huge_pte_lockptr(hstate_vma(vma), mm, pte);
+	__migration_entry_wait(mm, pte, ptl);
+}
+
+#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
+void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd)
+{
+	spinlock_t *ptl;
+	struct page *page;
+
+	ptl = pmd_lock(mm, pmd);
+	if (!is_pmd_migration_entry(*pmd))
+		goto unlock;
+	page = migration_entry_to_page(pmd_to_swp_entry(*pmd));
+	if (!get_page_unless_zero(page))
+		goto unlock;
+	spin_unlock(ptl);
+	wait_on_page_locked(page);
+	put_page(page);
+	return;
+unlock:
+	spin_unlock(ptl);
+}
+#endif
+
+#ifdef CONFIG_BLOCK
+/* Returns true if all buffers are successfully locked */
+static bool buffer_migrate_lock_buffers(struct buffer_head *head,
+							enum migrate_mode mode)
+{
+	struct buffer_head *bh = head;
+
+	/* Simple case, sync compaction */
+	if (mode != MIGRATE_ASYNC) {
+		do {
+			get_bh(bh);
+			lock_buffer(bh);
+			bh = bh->b_this_page;
+
+		} while (bh != head);
+
+		return true;
+	}
+
+	/* async case, we cannot block on lock_buffer so use trylock_buffer */
+	do {
+		get_bh(bh);
+		if (!trylock_buffer(bh)) {
+			/*
+			 * We failed to lock the buffer and cannot stall in
+			 * async migration. Release the taken locks
+			 */
+			struct buffer_head *failed_bh = bh;
+			put_bh(failed_bh);
+			bh = head;
+			while (bh != failed_bh) {
+				unlock_buffer(bh);
+				put_bh(bh);
+				bh = bh->b_this_page;
+			}
+			return false;
+		}
+
+		bh = bh->b_this_page;
+	} while (bh != head);
+	return true;
+}
+#else
+static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,
+							enum migrate_mode mode)
+{
+	return true;
+}
+#endif /* CONFIG_BLOCK */
+
+/*
+ * Replace the page in the mapping.
+ *
+ * The number of remaining references must be:
+ * 1 for anonymous pages without a mapping
+ * 2 for pages with a mapping
+ * 3 for pages with a mapping and PagePrivate/PagePrivate2 set.
+ */
+int migrate_page_move_mapping(struct address_space *mapping,
+		struct page *newpage, struct page *page,
+		struct buffer_head *head, enum migrate_mode mode,
+		int extra_count)
+{
+	struct zone *oldzone, *newzone;
+	int dirty;
+	int expected_count = 1 + extra_count;
+	void **pslot;
+
+	/*
+	 * Device public or private pages have an extra refcount as they are
+	 * ZONE_DEVICE pages.
+	 */
+	expected_count += is_device_private_page(page);
+	expected_count += is_device_public_page(page);
+
+	if (!mapping) {
+		/* Anonymous page without mapping */
+		if (page_count(page) != expected_count)
+			return -EAGAIN;
+
+		/* No turning back from here */
+		newpage->index = page->index;
+		newpage->mapping = page->mapping;
+		if (PageSwapBacked(page))
+			__SetPageSwapBacked(newpage);
+
+		return MIGRATEPAGE_SUCCESS;
+	}
+
+	oldzone = page_zone(page);
+	newzone = page_zone(newpage);
+
+	xa_lock_irq(&mapping->i_pages);
+
+	pslot = radix_tree_lookup_slot(&mapping->i_pages,
+ 					page_index(page));
+	if (pslot == NULL) {
+		xa_unlock_irq(&mapping->i_pages);
+		return -EAGAIN;
+	}
+
+	expected_count += hpage_nr_pages(page) + page_has_private(page);
+	if (page_count(page) != expected_count ||
+		radix_tree_deref_slot_protected(pslot,
+					&mapping->i_pages.xa_lock) != page) {
+		xa_unlock_irq(&mapping->i_pages);
+		return -EAGAIN;
+	}
+
+	if (!page_ref_freeze(page, expected_count)) {
+		xa_unlock_irq(&mapping->i_pages);
+		return -EAGAIN;
+	}
+
+	/*
+	 * In the async migration case of moving a page with buffers, lock the
+	 * buffers using trylock before the mapping is moved. If the mapping
+	 * was moved, we later failed to lock the buffers and could not move
+	 * the mapping back due to an elevated page count, we would have to
+	 * block waiting on other references to be dropped.
+	 */
+	if (mode == MIGRATE_ASYNC && head &&
+			!buffer_migrate_lock_buffers(head, mode)) {
+		page_ref_unfreeze(page, expected_count);
+		xa_unlock_irq(&mapping->i_pages);
+		return -EAGAIN;
+	}
+
+	/*
+	 * Now we know that no one else is looking at the page:
+	 * no turning back from here.
+	 */
+	newpage->index = page->index;
+	newpage->mapping = page->mapping;
+	page_ref_add(newpage, hpage_nr_pages(page)); /* add cache reference */
+	if (PageSwapBacked(page)) {
+		__SetPageSwapBacked(newpage);
+		if (PageSwapCache(page)) {
+			SetPageSwapCache(newpage);
+			set_page_private(newpage, page_private(page));
+		}
+	} else {
+		VM_BUG_ON_PAGE(PageSwapCache(page), page);
+	}
+
+	/* Move dirty while page refs frozen and newpage not yet exposed */
+	dirty = PageDirty(page);
+	if (dirty) {
+		ClearPageDirty(page);
+		SetPageDirty(newpage);
+	}
+
+	radix_tree_replace_slot(&mapping->i_pages, pslot, newpage);
+	if (PageTransHuge(page)) {
+		int i;
+		int index = page_index(page);
+
+		for (i = 1; i < HPAGE_PMD_NR; i++) {
+			pslot = radix_tree_lookup_slot(&mapping->i_pages,
+						       index + i);
+			radix_tree_replace_slot(&mapping->i_pages, pslot,
+						newpage + i);
+		}
+	}
+
+	/*
+	 * Drop cache reference from old page by unfreezing
+	 * to one less reference.
+	 * We know this isn't the last reference.
+	 */
+	page_ref_unfreeze(page, expected_count - hpage_nr_pages(page));
+
+	xa_unlock(&mapping->i_pages);
+	/* Leave irq disabled to prevent preemption while updating stats */
+
+	/*
+	 * If moved to a different zone then also account
+	 * the page for that zone. Other VM counters will be
+	 * taken care of when we establish references to the
+	 * new page and drop references to the old page.
+	 *
+	 * Note that anonymous pages are accounted for
+	 * via NR_FILE_PAGES and NR_ANON_MAPPED if they
+	 * are mapped to swap space.
+	 */
+	if (newzone != oldzone) {
+		__dec_node_state(oldzone->zone_pgdat, NR_FILE_PAGES);
+		__inc_node_state(newzone->zone_pgdat, NR_FILE_PAGES);
+		if (PageSwapBacked(page) && !PageSwapCache(page)) {
+			__dec_node_state(oldzone->zone_pgdat, NR_SHMEM);
+			__inc_node_state(newzone->zone_pgdat, NR_SHMEM);
+		}
+		if (dirty && mapping_cap_account_dirty(mapping)) {
+			__dec_node_state(oldzone->zone_pgdat, NR_FILE_DIRTY);
+			__dec_zone_state(oldzone, NR_ZONE_WRITE_PENDING);
+			__inc_node_state(newzone->zone_pgdat, NR_FILE_DIRTY);
+			__inc_zone_state(newzone, NR_ZONE_WRITE_PENDING);
+		}
+	}
+	local_irq_enable();
+
+	return MIGRATEPAGE_SUCCESS;
+}
+EXPORT_SYMBOL(migrate_page_move_mapping);
+
+/*
+ * The expected number of remaining references is the same as that
+ * of migrate_page_move_mapping().
+ */
+int migrate_huge_page_move_mapping(struct address_space *mapping,
+				   struct page *newpage, struct page *page)
+{
+	int expected_count;
+	void **pslot;
+
+	xa_lock_irq(&mapping->i_pages);
+
+	pslot = radix_tree_lookup_slot(&mapping->i_pages, page_index(page));
+	if (pslot == NULL) {
+		xa_unlock_irq(&mapping->i_pages);
+		return -EAGAIN;
+	}
+
+	expected_count = 2 + page_has_private(page);
+	if (page_count(page) != expected_count ||
+		radix_tree_deref_slot_protected(pslot, &mapping->i_pages.xa_lock) != page) {
+		xa_unlock_irq(&mapping->i_pages);
+		return -EAGAIN;
+	}
+
+	if (!page_ref_freeze(page, expected_count)) {
+		xa_unlock_irq(&mapping->i_pages);
+		return -EAGAIN;
+	}
+
+	newpage->index = page->index;
+	newpage->mapping = page->mapping;
+
+	get_page(newpage);
+
+	radix_tree_replace_slot(&mapping->i_pages, pslot, newpage);
+
+	page_ref_unfreeze(page, expected_count - 1);
+
+	xa_unlock_irq(&mapping->i_pages);
+
+	return MIGRATEPAGE_SUCCESS;
+}
+
+/*
+ * Gigantic pages are so large that we do not guarantee that page++ pointer
+ * arithmetic will work across the entire page.  We need something more
+ * specialized.
+ */
+static void __copy_gigantic_page(struct page *dst, struct page *src,
+				int nr_pages)
+{
+	int i;
+	struct page *dst_base = dst;
+	struct page *src_base = src;
+
+	for (i = 0; i < nr_pages; ) {
+		cond_resched();
+		copy_highpage(dst, src);
+
+		i++;
+		dst = mem_map_next(dst, dst_base, i);
+		src = mem_map_next(src, src_base, i);
+	}
+}
+
+static void copy_huge_page(struct page *dst, struct page *src)
+{
+	int i;
+	int nr_pages;
+
+	if (PageHuge(src)) {
+		/* hugetlbfs page */
+		struct hstate *h = page_hstate(src);
+		nr_pages = pages_per_huge_page(h);
+
+		if (unlikely(nr_pages > MAX_ORDER_NR_PAGES)) {
+			__copy_gigantic_page(dst, src, nr_pages);
+			return;
+		}
+	} else {
+		/* thp page */
+		BUG_ON(!PageTransHuge(src));
+		nr_pages = hpage_nr_pages(src);
+	}
+
+	for (i = 0; i < nr_pages; i++) {
+		cond_resched();
+		copy_highpage(dst + i, src + i);
+	}
+}
+
+/*
+ * Copy the page to its new location
+ */
+void migrate_page_states(struct page *newpage, struct page *page)
+{
+	int cpupid;
+
+	if (PageError(page))
+		SetPageError(newpage);
+	if (PageReferenced(page))
+		SetPageReferenced(newpage);
+	if (PageUptodate(page))
+		SetPageUptodate(newpage);
+	if (TestClearPageActive(page)) {
+		VM_BUG_ON_PAGE(PageUnevictable(page), page);
+		SetPageActive(newpage);
+	} else if (TestClearPageUnevictable(page))
+		SetPageUnevictable(newpage);
+	if (PageChecked(page))
+		SetPageChecked(newpage);
+	if (PageMappedToDisk(page))
+		SetPageMappedToDisk(newpage);
+
+	/* Move dirty on pages not done by migrate_page_move_mapping() */
+	if (PageDirty(page))
+		SetPageDirty(newpage);
+
+	if (page_is_young(page))
+		set_page_young(newpage);
+	if (page_is_idle(page))
+		set_page_idle(newpage);
+
+	/*
+	 * Copy NUMA information to the new page, to prevent over-eager
+	 * future migrations of this same page.
+	 */
+	cpupid = page_cpupid_xchg_last(page, -1);
+	page_cpupid_xchg_last(newpage, cpupid);
+
+	ksm_migrate_page(newpage, page);
+	/*
+	 * Please do not reorder this without considering how mm/ksm.c's
+	 * get_ksm_page() depends upon ksm_migrate_page() and PageSwapCache().
+	 */
+	if (PageSwapCache(page))
+		ClearPageSwapCache(page);
+	ClearPagePrivate(page);
+	set_page_private(page, 0);
+
+	/*
+	 * If any waiters have accumulated on the new page then
+	 * wake them up.
+	 */
+	if (PageWriteback(newpage))
+		end_page_writeback(newpage);
+
+	copy_page_owner(page, newpage);
+
+	mem_cgroup_migrate(page, newpage);
+}
+EXPORT_SYMBOL(migrate_page_states);
+
+void migrate_page_copy(struct page *newpage, struct page *page)
+{
+	if (PageHuge(page) || PageTransHuge(page))
+		copy_huge_page(newpage, page);
+	else
+		copy_highpage(newpage, page);
+
+	migrate_page_states(newpage, page);
+}
+EXPORT_SYMBOL(migrate_page_copy);
+
+/************************************************************
+ *                    Migration functions
+ ***********************************************************/
+
+/*
+ * Common logic to directly migrate a single LRU page suitable for
+ * pages that do not use PagePrivate/PagePrivate2.
+ *
+ * Pages are locked upon entry and exit.
+ */
+int migrate_page(struct address_space *mapping,
+		struct page *newpage, struct page *page,
+		enum migrate_mode mode)
+{
+	int rc;
+
+	BUG_ON(PageWriteback(page));	/* Writeback must be complete */
+
+	rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0);
+
+	if (rc != MIGRATEPAGE_SUCCESS)
+		return rc;
+
+	if (mode != MIGRATE_SYNC_NO_COPY)
+		migrate_page_copy(newpage, page);
+	else
+		migrate_page_states(newpage, page);
+	return MIGRATEPAGE_SUCCESS;
+}
+EXPORT_SYMBOL(migrate_page);
+
+#ifdef CONFIG_BLOCK
+/*
+ * Migration function for pages with buffers. This function can only be used
+ * if the underlying filesystem guarantees that no other references to "page"
+ * exist.
+ */
+int buffer_migrate_page(struct address_space *mapping,
+		struct page *newpage, struct page *page, enum migrate_mode mode)
+{
+	struct buffer_head *bh, *head;
+	int rc;
+
+	if (!page_has_buffers(page))
+		return migrate_page(mapping, newpage, page, mode);
+
+	head = page_buffers(page);
+
+	rc = migrate_page_move_mapping(mapping, newpage, page, head, mode, 0);
+
+	if (rc != MIGRATEPAGE_SUCCESS)
+		return rc;
+
+	/*
+	 * In the async case, migrate_page_move_mapping locked the buffers
+	 * with an IRQ-safe spinlock held. In the sync case, the buffers
+	 * need to be locked now
+	 */
+	if (mode != MIGRATE_ASYNC)
+		BUG_ON(!buffer_migrate_lock_buffers(head, mode));
+
+	ClearPagePrivate(page);
+	set_page_private(newpage, page_private(page));
+	set_page_private(page, 0);
+	put_page(page);
+	get_page(newpage);
+
+	bh = head;
+	do {
+		set_bh_page(bh, newpage, bh_offset(bh));
+		bh = bh->b_this_page;
+
+	} while (bh != head);
+
+	SetPagePrivate(newpage);
+
+	if (mode != MIGRATE_SYNC_NO_COPY)
+		migrate_page_copy(newpage, page);
+	else
+		migrate_page_states(newpage, page);
+
+	bh = head;
+	do {
+		unlock_buffer(bh);
+		put_bh(bh);
+		bh = bh->b_this_page;
+
+	} while (bh != head);
+
+	return MIGRATEPAGE_SUCCESS;
+}
+EXPORT_SYMBOL(buffer_migrate_page);
+#endif
+
+/*
+ * Writeback a page to clean the dirty state
+ */
+static int writeout(struct address_space *mapping, struct page *page)
+{
+	struct writeback_control wbc = {
+		.sync_mode = WB_SYNC_NONE,
+		.nr_to_write = 1,
+		.range_start = 0,
+		.range_end = LLONG_MAX,
+		.for_reclaim = 1
+	};
+	int rc;
+
+	if (!mapping->a_ops->writepage)
+		/* No write method for the address space */
+		return -EINVAL;
+
+	if (!clear_page_dirty_for_io(page))
+		/* Someone else already triggered a write */
+		return -EAGAIN;
+
+	/*
+	 * A dirty page may imply that the underlying filesystem has
+	 * the page on some queue. So the page must be clean for
+	 * migration. Writeout may mean we loose the lock and the
+	 * page state is no longer what we checked for earlier.
+	 * At this point we know that the migration attempt cannot
+	 * be successful.
+	 */
+	remove_migration_ptes(page, page, false);
+
+	rc = mapping->a_ops->writepage(page, &wbc);
+
+	if (rc != AOP_WRITEPAGE_ACTIVATE)
+		/* unlocked. Relock */
+		lock_page(page);
+
+	return (rc < 0) ? -EIO : -EAGAIN;
+}
+
+/*
+ * Default handling if a filesystem does not provide a migration function.
+ */
+static int fallback_migrate_page(struct address_space *mapping,
+	struct page *newpage, struct page *page, enum migrate_mode mode)
+{
+	if (PageDirty(page)) {
+		/* Only writeback pages in full synchronous migration */
+		switch (mode) {
+		case MIGRATE_SYNC:
+		case MIGRATE_SYNC_NO_COPY:
+			break;
+		default:
+			return -EBUSY;
+		}
+		return writeout(mapping, page);
+	}
+
+	/*
+	 * Buffers may be managed in a filesystem specific way.
+	 * We must have no buffers or drop them.
+	 */
+	if (page_has_private(page) &&
+	    !try_to_release_page(page, GFP_KERNEL))
+		return -EAGAIN;
+
+	return migrate_page(mapping, newpage, page, mode);
+}
+
+/*
+ * Move a page to a newly allocated page
+ * The page is locked and all ptes have been successfully removed.
+ *
+ * The new page will have replaced the old page if this function
+ * is successful.
+ *
+ * Return value:
+ *   < 0 - error code
+ *  MIGRATEPAGE_SUCCESS - success
+ */
+static int move_to_new_page(struct page *newpage, struct page *page,
+				enum migrate_mode mode)
+{
+	struct address_space *mapping;
+	int rc = -EAGAIN;
+	bool is_lru = !__PageMovable(page);
+
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
+
+	mapping = page_mapping(page);
+
+	if (likely(is_lru)) {
+		if (!mapping)
+			rc = migrate_page(mapping, newpage, page, mode);
+		else if (mapping->a_ops->migratepage)
+			/*
+			 * Most pages have a mapping and most filesystems
+			 * provide a migratepage callback. Anonymous pages
+			 * are part of swap space which also has its own
+			 * migratepage callback. This is the most common path
+			 * for page migration.
+			 */
+			rc = mapping->a_ops->migratepage(mapping, newpage,
+							page, mode);
+		else
+			rc = fallback_migrate_page(mapping, newpage,
+							page, mode);
+	} else {
+		/*
+		 * In case of non-lru page, it could be released after
+		 * isolation step. In that case, we shouldn't try migration.
+		 */
+		VM_BUG_ON_PAGE(!PageIsolated(page), page);
+		if (!PageMovable(page)) {
+			rc = MIGRATEPAGE_SUCCESS;
+			__ClearPageIsolated(page);
+			goto out;
+		}
+
+		rc = mapping->a_ops->migratepage(mapping, newpage,
+						page, mode);
+		WARN_ON_ONCE(rc == MIGRATEPAGE_SUCCESS &&
+			!PageIsolated(page));
+	}
+
+	/*
+	 * When successful, old pagecache page->mapping must be cleared before
+	 * page is freed; but stats require that PageAnon be left as PageAnon.
+	 */
+	if (rc == MIGRATEPAGE_SUCCESS) {
+		if (__PageMovable(page)) {
+			VM_BUG_ON_PAGE(!PageIsolated(page), page);
+
+			/*
+			 * We clear PG_movable under page_lock so any compactor
+			 * cannot try to migrate this page.
+			 */
+			__ClearPageIsolated(page);
+		}
+
+		/*
+		 * Anonymous and movable page->mapping will be cleard by
+		 * free_pages_prepare so don't reset it here for keeping
+		 * the type to work PageAnon, for example.
+		 */
+		if (!PageMappingFlags(page))
+			page->mapping = NULL;
+
+		if (unlikely(is_zone_device_page(newpage))) {
+			if (is_device_public_page(newpage))
+				flush_dcache_page(newpage);
+		} else
+			flush_dcache_page(newpage);
+
+	}
+out:
+	return rc;
+}
+
+static int __unmap_and_move(struct page *page, struct page *newpage,
+				int force, enum migrate_mode mode)
+{
+	int rc = -EAGAIN;
+	int page_was_mapped = 0;
+	struct anon_vma *anon_vma = NULL;
+	bool is_lru = !__PageMovable(page);
+
+	if (!trylock_page(page)) {
+		if (!force || mode == MIGRATE_ASYNC)
+			goto out;
+
+		/*
+		 * It's not safe for direct compaction to call lock_page.
+		 * For example, during page readahead pages are added locked
+		 * to the LRU. Later, when the IO completes the pages are
+		 * marked uptodate and unlocked. However, the queueing
+		 * could be merging multiple pages for one bio (e.g.
+		 * mpage_readpages). If an allocation happens for the
+		 * second or third page, the process can end up locking
+		 * the same page twice and deadlocking. Rather than
+		 * trying to be clever about what pages can be locked,
+		 * avoid the use of lock_page for direct compaction
+		 * altogether.
+		 */
+		if (current->flags & PF_MEMALLOC)
+			goto out;
+
+		lock_page(page);
+	}
+
+	if (PageWriteback(page)) {
+		/*
+		 * Only in the case of a full synchronous migration is it
+		 * necessary to wait for PageWriteback. In the async case,
+		 * the retry loop is too short and in the sync-light case,
+		 * the overhead of stalling is too much
+		 */
+		switch (mode) {
+		case MIGRATE_SYNC:
+		case MIGRATE_SYNC_NO_COPY:
+			break;
+		default:
+			rc = -EBUSY;
+			goto out_unlock;
+		}
+		if (!force)
+			goto out_unlock;
+		wait_on_page_writeback(page);
+	}
+
+	/*
+	 * By try_to_unmap(), page->mapcount goes down to 0 here. In this case,
+	 * we cannot notice that anon_vma is freed while we migrates a page.
+	 * This get_anon_vma() delays freeing anon_vma pointer until the end
+	 * of migration. File cache pages are no problem because of page_lock()
+	 * File Caches may use write_page() or lock_page() in migration, then,
+	 * just care Anon page here.
+	 *
+	 * Only page_get_anon_vma() understands the subtleties of
+	 * getting a hold on an anon_vma from outside one of its mms.
+	 * But if we cannot get anon_vma, then we won't need it anyway,
+	 * because that implies that the anon page is no longer mapped
+	 * (and cannot be remapped so long as we hold the page lock).
+	 */
+	if (PageAnon(page) && !PageKsm(page))
+		anon_vma = page_get_anon_vma(page);
+
+	/*
+	 * Block others from accessing the new page when we get around to
+	 * establishing additional references. We are usually the only one
+	 * holding a reference to newpage at this point. We used to have a BUG
+	 * here if trylock_page(newpage) fails, but would like to allow for
+	 * cases where there might be a race with the previous use of newpage.
+	 * This is much like races on refcount of oldpage: just don't BUG().
+	 */
+	if (unlikely(!trylock_page(newpage)))
+		goto out_unlock;
+
+	if (unlikely(!is_lru)) {
+		rc = move_to_new_page(newpage, page, mode);
+		goto out_unlock_both;
+	}
+
+	/*
+	 * Corner case handling:
+	 * 1. When a new swap-cache page is read into, it is added to the LRU
+	 * and treated as swapcache but it has no rmap yet.
+	 * Calling try_to_unmap() against a page->mapping==NULL page will
+	 * trigger a BUG.  So handle it here.
+	 * 2. An orphaned page (see truncate_complete_page) might have
+	 * fs-private metadata. The page can be picked up due to memory
+	 * offlining.  Everywhere else except page reclaim, the page is
+	 * invisible to the vm, so the page can not be migrated.  So try to
+	 * free the metadata, so the page can be freed.
+	 */
+	if (!page->mapping) {
+		VM_BUG_ON_PAGE(PageAnon(page), page);
+		if (page_has_private(page)) {
+			try_to_free_buffers(page);
+			goto out_unlock_both;
+		}
+	} else if (page_mapped(page)) {
+		/* Establish migration ptes */
+		VM_BUG_ON_PAGE(PageAnon(page) && !PageKsm(page) && !anon_vma,
+				page);
+		try_to_unmap(page,
+			TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
+		page_was_mapped = 1;
+	}
+
+	if (!page_mapped(page))
+		rc = move_to_new_page(newpage, page, mode);
+
+	if (page_was_mapped)
+		remove_migration_ptes(page,
+			rc == MIGRATEPAGE_SUCCESS ? newpage : page, false);
+
+out_unlock_both:
+	unlock_page(newpage);
+out_unlock:
+	/* Drop an anon_vma reference if we took one */
+	if (anon_vma)
+		put_anon_vma(anon_vma);
+	unlock_page(page);
+out:
+	/*
+	 * If migration is successful, decrease refcount of the newpage
+	 * which will not free the page because new page owner increased
+	 * refcounter. As well, if it is LRU page, add the page to LRU
+	 * list in here. Use the old state of the isolated source page to
+	 * determine if we migrated a LRU page. newpage was already unlocked
+	 * and possibly modified by its owner - don't rely on the page
+	 * state.
+	 */
+	if (rc == MIGRATEPAGE_SUCCESS) {
+		if (unlikely(!is_lru))
+			put_page(newpage);
+		else
+			putback_lru_page(newpage);
+	}
+
+	return rc;
+}
+
+/*
+ * gcc 4.7 and 4.8 on arm get an ICEs when inlining unmap_and_move().  Work
+ * around it.
+ */
+#if defined(CONFIG_ARM) && \
+	defined(GCC_VERSION) && GCC_VERSION < 40900 && GCC_VERSION >= 40700
+#define ICE_noinline noinline
+#else
+#define ICE_noinline
+#endif
+
+/*
+ * Obtain the lock on page, remove all ptes and migrate the page
+ * to the newly allocated page in newpage.
+ */
+static ICE_noinline int unmap_and_move(new_page_t get_new_page,
+				   free_page_t put_new_page,
+				   unsigned long private, struct page *page,
+				   int force, enum migrate_mode mode,
+				   enum migrate_reason reason)
+{
+	int rc = MIGRATEPAGE_SUCCESS;
+	struct page *newpage;
+
+	if (!thp_migration_supported() && PageTransHuge(page))
+		return -ENOMEM;
+
+	newpage = get_new_page(page, private);
+	if (!newpage)
+		return -ENOMEM;
+
+	if (page_count(page) == 1) {
+		/* page was freed from under us. So we are done. */
+		ClearPageActive(page);
+		ClearPageUnevictable(page);
+		if (unlikely(__PageMovable(page))) {
+			lock_page(page);
+			if (!PageMovable(page))
+				__ClearPageIsolated(page);
+			unlock_page(page);
+		}
+		if (put_new_page)
+			put_new_page(newpage, private);
+		else
+			put_page(newpage);
+		goto out;
+	}
+
+	rc = __unmap_and_move(page, newpage, force, mode);
+	if (rc == MIGRATEPAGE_SUCCESS)
+		set_page_owner_migrate_reason(newpage, reason);
+
+out:
+	if (rc != -EAGAIN) {
+		/*
+		 * A page that has been migrated has all references
+		 * removed and will be freed. A page that has not been
+		 * migrated will have kepts its references and be
+		 * restored.
+		 */
+		list_del(&page->lru);
+
+		/*
+		 * Compaction can migrate also non-LRU pages which are
+		 * not accounted to NR_ISOLATED_*. They can be recognized
+		 * as __PageMovable
+		 */
+		if (likely(!__PageMovable(page)))
+			mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON +
+					page_is_file_cache(page), -hpage_nr_pages(page));
+	}
+
+	/*
+	 * If migration is successful, releases reference grabbed during
+	 * isolation. Otherwise, restore the page to right list unless
+	 * we want to retry.
+	 */
+	if (rc == MIGRATEPAGE_SUCCESS) {
+		put_page(page);
+		if (reason == MR_MEMORY_FAILURE) {
+			/*
+			 * Set PG_HWPoison on just freed page
+			 * intentionally. Although it's rather weird,
+			 * it's how HWPoison flag works at the moment.
+			 */
+			if (set_hwpoison_free_buddy_page(page))
+				num_poisoned_pages_inc();
+		}
+	} else {
+		if (rc != -EAGAIN) {
+			if (likely(!__PageMovable(page))) {
+				putback_lru_page(page);
+				goto put_new;
+			}
+
+			lock_page(page);
+			if (PageMovable(page))
+				putback_movable_page(page);
+			else
+				__ClearPageIsolated(page);
+			unlock_page(page);
+			put_page(page);
+		}
+put_new:
+		if (put_new_page)
+			put_new_page(newpage, private);
+		else
+			put_page(newpage);
+	}
+
+	return rc;
+}
+
+/*
+ * Counterpart of unmap_and_move_page() for hugepage migration.
+ *
+ * This function doesn't wait the completion of hugepage I/O
+ * because there is no race between I/O and migration for hugepage.
+ * Note that currently hugepage I/O occurs only in direct I/O
+ * where no lock is held and PG_writeback is irrelevant,
+ * and writeback status of all subpages are counted in the reference
+ * count of the head page (i.e. if all subpages of a 2MB hugepage are
+ * under direct I/O, the reference of the head page is 512 and a bit more.)
+ * This means that when we try to migrate hugepage whose subpages are
+ * doing direct I/O, some references remain after try_to_unmap() and
+ * hugepage migration fails without data corruption.
+ *
+ * There is also no race when direct I/O is issued on the page under migration,
+ * because then pte is replaced with migration swap entry and direct I/O code
+ * will wait in the page fault for migration to complete.
+ */
+static int unmap_and_move_huge_page(new_page_t get_new_page,
+				free_page_t put_new_page, unsigned long private,
+				struct page *hpage, int force,
+				enum migrate_mode mode, int reason)
+{
+	int rc = -EAGAIN;
+	int page_was_mapped = 0;
+	struct page *new_hpage;
+	struct anon_vma *anon_vma = NULL;
+
+	/*
+	 * Movability of hugepages depends on architectures and hugepage size.
+	 * This check is necessary because some callers of hugepage migration
+	 * like soft offline and memory hotremove don't walk through page
+	 * tables or check whether the hugepage is pmd-based or not before
+	 * kicking migration.
+	 */
+	if (!hugepage_migration_supported(page_hstate(hpage))) {
+		putback_active_hugepage(hpage);
+		return -ENOSYS;
+	}
+
+	new_hpage = get_new_page(hpage, private);
+	if (!new_hpage)
+		return -ENOMEM;
+
+	if (!trylock_page(hpage)) {
+		if (!force)
+			goto out;
+		switch (mode) {
+		case MIGRATE_SYNC:
+		case MIGRATE_SYNC_NO_COPY:
+			break;
+		default:
+			goto out;
+		}
+		lock_page(hpage);
+	}
+
+	/*
+	 * Check for pages which are in the process of being freed.  Without
+	 * page_mapping() set, hugetlbfs specific move page routine will not
+	 * be called and we could leak usage counts for subpools.
+	 */
+	if (page_private(hpage) && !page_mapping(hpage)) {
+		rc = -EBUSY;
+		goto out_unlock;
+	}
+
+	if (PageAnon(hpage))
+		anon_vma = page_get_anon_vma(hpage);
+
+	if (unlikely(!trylock_page(new_hpage)))
+		goto put_anon;
+
+	if (page_mapped(hpage)) {
+		try_to_unmap(hpage,
+			TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
+		page_was_mapped = 1;
+	}
+
+	if (!page_mapped(hpage))
+		rc = move_to_new_page(new_hpage, hpage, mode);
+
+	if (page_was_mapped)
+		remove_migration_ptes(hpage,
+			rc == MIGRATEPAGE_SUCCESS ? new_hpage : hpage, false);
+
+	unlock_page(new_hpage);
+
+put_anon:
+	if (anon_vma)
+		put_anon_vma(anon_vma);
+
+	if (rc == MIGRATEPAGE_SUCCESS) {
+		move_hugetlb_state(hpage, new_hpage, reason);
+		put_new_page = NULL;
+	}
+
+out_unlock:
+	unlock_page(hpage);
+out:
+	if (rc != -EAGAIN)
+		putback_active_hugepage(hpage);
+
+	/*
+	 * If migration was not successful and there's a freeing callback, use
+	 * it.  Otherwise, put_page() will drop the reference grabbed during
+	 * isolation.
+	 */
+	if (put_new_page)
+		put_new_page(new_hpage, private);
+	else
+		putback_active_hugepage(new_hpage);
+
+	return rc;
+}
+
+/*
+ * migrate_pages - migrate the pages specified in a list, to the free pages
+ *		   supplied as the target for the page migration
+ *
+ * @from:		The list of pages to be migrated.
+ * @get_new_page:	The function used to allocate free pages to be used
+ *			as the target of the page migration.
+ * @put_new_page:	The function used to free target pages if migration
+ *			fails, or NULL if no special handling is necessary.
+ * @private:		Private data to be passed on to get_new_page()
+ * @mode:		The migration mode that specifies the constraints for
+ *			page migration, if any.
+ * @reason:		The reason for page migration.
+ *
+ * The function returns after 10 attempts or if no pages are movable any more
+ * because the list has become empty or no retryable pages exist any more.
+ * The caller should call putback_movable_pages() to return pages to the LRU
+ * or free list only if ret != 0.
+ *
+ * Returns the number of pages that were not migrated, or an error code.
+ */
+int migrate_pages(struct list_head *from, new_page_t get_new_page,
+		free_page_t put_new_page, unsigned long private,
+		enum migrate_mode mode, int reason)
+{
+	int retry = 1;
+	int nr_failed = 0;
+	int nr_succeeded = 0;
+	int pass = 0;
+	struct page *page;
+	struct page *page2;
+	int swapwrite = current->flags & PF_SWAPWRITE;
+	int rc;
+
+	if (!swapwrite)
+		current->flags |= PF_SWAPWRITE;
+
+	for(pass = 0; pass < 10 && retry; pass++) {
+		retry = 0;
+
+		list_for_each_entry_safe(page, page2, from, lru) {
+retry:
+			cond_resched();
+
+			if (PageHuge(page))
+				rc = unmap_and_move_huge_page(get_new_page,
+						put_new_page, private, page,
+						pass > 2, mode, reason);
+			else
+				rc = unmap_and_move(get_new_page, put_new_page,
+						private, page, pass > 2, mode,
+						reason);
+
+			switch(rc) {
+			case -ENOMEM:
+				/*
+				 * THP migration might be unsupported or the
+				 * allocation could've failed so we should
+				 * retry on the same page with the THP split
+				 * to base pages.
+				 *
+				 * Head page is retried immediately and tail
+				 * pages are added to the tail of the list so
+				 * we encounter them after the rest of the list
+				 * is processed.
+				 */
+				if (PageTransHuge(page) && !PageHuge(page)) {
+					lock_page(page);
+					rc = split_huge_page_to_list(page, from);
+					unlock_page(page);
+					if (!rc) {
+						list_safe_reset_next(page, page2, lru);
+						goto retry;
+					}
+				}
+				nr_failed++;
+				goto out;
+			case -EAGAIN:
+				retry++;
+				break;
+			case MIGRATEPAGE_SUCCESS:
+				nr_succeeded++;
+				break;
+			default:
+				/*
+				 * Permanent failure (-EBUSY, -ENOSYS, etc.):
+				 * unlike -EAGAIN case, the failed page is
+				 * removed from migration page list and not
+				 * retried in the next outer loop.
+				 */
+				nr_failed++;
+				break;
+			}
+		}
+	}
+	nr_failed += retry;
+	rc = nr_failed;
+out:
+	if (nr_succeeded)
+		count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
+	if (nr_failed)
+		count_vm_events(PGMIGRATE_FAIL, nr_failed);
+	trace_mm_migrate_pages(nr_succeeded, nr_failed, mode, reason);
+
+	if (!swapwrite)
+		current->flags &= ~PF_SWAPWRITE;
+
+	return rc;
+}
+
+#ifdef CONFIG_NUMA
+
+static int store_status(int __user *status, int start, int value, int nr)
+{
+	while (nr-- > 0) {
+		if (put_user(value, status + start))
+			return -EFAULT;
+		start++;
+	}
+
+	return 0;
+}
+
+static int do_move_pages_to_node(struct mm_struct *mm,
+		struct list_head *pagelist, int node)
+{
+	int err;
+
+	if (list_empty(pagelist))
+		return 0;
+
+	err = migrate_pages(pagelist, alloc_new_node_page, NULL, node,
+			MIGRATE_SYNC, MR_SYSCALL);
+	if (err)
+		putback_movable_pages(pagelist);
+	return err;
+}
+
+/*
+ * Resolves the given address to a struct page, isolates it from the LRU and
+ * puts it to the given pagelist.
+ * Returns:
+ *     errno - if the page cannot be found/isolated
+ *     0 - when it doesn't have to be migrated because it is already on the
+ *         target node
+ *     1 - when it has been queued
+ */
+static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
+		int node, struct list_head *pagelist, bool migrate_all)
+{
+	struct vm_area_struct *vma;
+	struct page *page;
+	unsigned int follflags;
+	int err;
+
+	down_read(&mm->mmap_sem);
+	err = -EFAULT;
+	vma = find_vma(mm, addr);
+	if (!vma || addr < vma->vm_start || !vma_migratable(vma))
+		goto out;
+
+	/* FOLL_DUMP to ignore special (like zero) pages */
+	follflags = FOLL_GET | FOLL_DUMP;
+	page = follow_page(vma, addr, follflags);
+
+	err = PTR_ERR(page);
+	if (IS_ERR(page))
+		goto out;
+
+	err = -ENOENT;
+	if (!page)
+		goto out;
+
+	err = 0;
+	if (page_to_nid(page) == node)
+		goto out_putpage;
+
+	err = -EACCES;
+	if (page_mapcount(page) > 1 && !migrate_all)
+		goto out_putpage;
+
+	if (PageHuge(page)) {
+		if (PageHead(page)) {
+			isolate_huge_page(page, pagelist);
+			err = 1;
+		}
+	} else {
+		struct page *head;
+
+		head = compound_head(page);
+		err = isolate_lru_page(head);
+		if (err)
+			goto out_putpage;
+
+		err = 1;
+		list_add_tail(&head->lru, pagelist);
+		mod_node_page_state(page_pgdat(head),
+			NR_ISOLATED_ANON + page_is_file_cache(head),
+			hpage_nr_pages(head));
+	}
+out_putpage:
+	/*
+	 * Either remove the duplicate refcount from
+	 * isolate_lru_page() or drop the page ref if it was
+	 * not isolated.
+	 */
+	put_page(page);
+out:
+	up_read(&mm->mmap_sem);
+	return err;
+}
+
+/*
+ * Migrate an array of page address onto an array of nodes and fill
+ * the corresponding array of status.
+ */
+static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
+			 unsigned long nr_pages,
+			 const void __user * __user *pages,
+			 const int __user *nodes,
+			 int __user *status, int flags)
+{
+	int current_node = NUMA_NO_NODE;
+	LIST_HEAD(pagelist);
+	int start, i;
+	int err = 0, err1;
+
+	migrate_prep();
+
+	for (i = start = 0; i < nr_pages; i++) {
+		const void __user *p;
+		unsigned long addr;
+		int node;
+
+		err = -EFAULT;
+		if (get_user(p, pages + i))
+			goto out_flush;
+		if (get_user(node, nodes + i))
+			goto out_flush;
+		addr = (unsigned long)p;
+
+		err = -ENODEV;
+		if (node < 0 || node >= MAX_NUMNODES)
+			goto out_flush;
+		if (!node_state(node, N_MEMORY))
+			goto out_flush;
+
+		err = -EACCES;
+		if (!node_isset(node, task_nodes))
+			goto out_flush;
+
+		if (current_node == NUMA_NO_NODE) {
+			current_node = node;
+			start = i;
+		} else if (node != current_node) {
+			err = do_move_pages_to_node(mm, &pagelist, current_node);
+			if (err) {
+				/*
+				 * Positive err means the number of failed
+				 * pages to migrate.  Since we are going to
+				 * abort and return the number of non-migrated
+				 * pages, so need to incude the rest of the
+				 * nr_pages that have not been attempted as
+				 * well.
+				 */
+				if (err > 0)
+					err += nr_pages - i - 1;
+				goto out;
+			}
+			err = store_status(status, start, current_node, i - start);
+			if (err)
+				goto out;
+			start = i;
+			current_node = node;
+		}
+
+		/*
+		 * Errors in the page lookup or isolation are not fatal and we simply
+		 * report them via status
+		 */
+		err = add_page_for_migration(mm, addr, current_node,
+				&pagelist, flags & MPOL_MF_MOVE_ALL);
+
+		if (!err) {
+			/* The page is already on the target node */
+			err = store_status(status, i, current_node, 1);
+			if (err)
+				goto out_flush;
+			continue;
+		} else if (err > 0) {
+			/* The page is successfully queued for migration */
+			continue;
+		}
+
+		err = store_status(status, i, err, 1);
+		if (err)
+			goto out_flush;
+
+		err = do_move_pages_to_node(mm, &pagelist, current_node);
+		if (err) {
+			if (err > 0)
+				err += nr_pages - i - 1;
+			goto out;
+		}
+		if (i > start) {
+			err = store_status(status, start, current_node, i - start);
+			if (err)
+				goto out;
+		}
+		current_node = NUMA_NO_NODE;
+	}
+out_flush:
+	if (list_empty(&pagelist))
+		return err;
+
+	/* Make sure we do not overwrite the existing error */
+	err1 = do_move_pages_to_node(mm, &pagelist, current_node);
+	/*
+	 * Don't have to report non-attempted pages here since:
+	 *     - If the above loop is done gracefully all pages have been
+	 *       attempted.
+	 *     - If the above loop is aborted it means a fatal error
+	 *       happened, should return ret.
+	 */
+	if (!err1)
+		err1 = store_status(status, start, current_node, i - start);
+	if (err >= 0)
+		err = err1;
+out:
+	return err;
+}
+
+/*
+ * Determine the nodes of an array of pages and store it in an array of status.
+ */
+static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
+				const void __user **pages, int *status)
+{
+	unsigned long i;
+
+	down_read(&mm->mmap_sem);
+
+	for (i = 0; i < nr_pages; i++) {
+		unsigned long addr = (unsigned long)(*pages);
+		struct vm_area_struct *vma;
+		struct page *page;
+		int err = -EFAULT;
+
+		vma = find_vma(mm, addr);
+		if (!vma || addr < vma->vm_start)
+			goto set_status;
+
+		/* FOLL_DUMP to ignore special (like zero) pages */
+		page = follow_page(vma, addr, FOLL_DUMP);
+
+		err = PTR_ERR(page);
+		if (IS_ERR(page))
+			goto set_status;
+
+		err = page ? page_to_nid(page) : -ENOENT;
+set_status:
+		*status = err;
+
+		pages++;
+		status++;
+	}
+
+	up_read(&mm->mmap_sem);
+}
+
+/*
+ * Determine the nodes of a user array of pages and store it in
+ * a user array of status.
+ */
+static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
+			 const void __user * __user *pages,
+			 int __user *status)
+{
+#define DO_PAGES_STAT_CHUNK_NR 16
+	const void __user *chunk_pages[DO_PAGES_STAT_CHUNK_NR];
+	int chunk_status[DO_PAGES_STAT_CHUNK_NR];
+
+	while (nr_pages) {
+		unsigned long chunk_nr;
+
+		chunk_nr = nr_pages;
+		if (chunk_nr > DO_PAGES_STAT_CHUNK_NR)
+			chunk_nr = DO_PAGES_STAT_CHUNK_NR;
+
+		if (copy_from_user(chunk_pages, pages, chunk_nr * sizeof(*chunk_pages)))
+			break;
+
+		do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);
+
+		if (copy_to_user(status, chunk_status, chunk_nr * sizeof(*status)))
+			break;
+
+		pages += chunk_nr;
+		status += chunk_nr;
+		nr_pages -= chunk_nr;
+	}
+	return nr_pages ? -EFAULT : 0;
+}
+
+/*
+ * Move a list of pages in the address space of the currently executing
+ * process.
+ */
+static int kernel_move_pages(pid_t pid, unsigned long nr_pages,
+			     const void __user * __user *pages,
+			     const int __user *nodes,
+			     int __user *status, int flags)
+{
+	struct task_struct *task;
+	struct mm_struct *mm;
+	int err;
+	nodemask_t task_nodes;
+
+	/* Check flags */
+	if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL))
+		return -EINVAL;
+
+	if ((flags & MPOL_MF_MOVE_ALL) && !capable(CAP_SYS_NICE))
+		return -EPERM;
+
+	/* Find the mm_struct */
+	rcu_read_lock();
+	task = pid ? find_task_by_vpid(pid) : current;
+	if (!task) {
+		rcu_read_unlock();
+		return -ESRCH;
+	}
+	get_task_struct(task);
+
+	/*
+	 * Check if this process has the right to modify the specified
+	 * process. Use the regular "ptrace_may_access()" checks.
+	 */
+	if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) {
+		rcu_read_unlock();
+		err = -EPERM;
+		goto out;
+	}
+	rcu_read_unlock();
+
+ 	err = security_task_movememory(task);
+ 	if (err)
+		goto out;
+
+	task_nodes = cpuset_mems_allowed(task);
+	mm = get_task_mm(task);
+	put_task_struct(task);
+
+	if (!mm)
+		return -EINVAL;
+
+	if (nodes)
+		err = do_pages_move(mm, task_nodes, nr_pages, pages,
+				    nodes, status, flags);
+	else
+		err = do_pages_stat(mm, nr_pages, pages, status);
+
+	mmput(mm);
+	return err;
+
+out:
+	put_task_struct(task);
+	return err;
+}
+
+SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
+		const void __user * __user *, pages,
+		const int __user *, nodes,
+		int __user *, status, int, flags)
+{
+	return kernel_move_pages(pid, nr_pages, pages, nodes, status, flags);
+}
+
+#ifdef CONFIG_COMPAT
+COMPAT_SYSCALL_DEFINE6(move_pages, pid_t, pid, compat_ulong_t, nr_pages,
+		       compat_uptr_t __user *, pages32,
+		       const int __user *, nodes,
+		       int __user *, status,
+		       int, flags)
+{
+	const void __user * __user *pages;
+	int i;
+
+	pages = compat_alloc_user_space(nr_pages * sizeof(void *));
+	for (i = 0; i < nr_pages; i++) {
+		compat_uptr_t p;
+
+		if (get_user(p, pages32 + i) ||
+			put_user(compat_ptr(p), pages + i))
+			return -EFAULT;
+	}
+	return kernel_move_pages(pid, nr_pages, pages, nodes, status, flags);
+}
+#endif /* CONFIG_COMPAT */
+
+#ifdef CONFIG_NUMA_BALANCING
+/*
+ * Returns true if this is a safe migration target node for misplaced NUMA
+ * pages. Currently it only checks the watermarks which crude
+ */
+static bool migrate_balanced_pgdat(struct pglist_data *pgdat,
+				   unsigned long nr_migrate_pages)
+{
+	int z;
+
+	for (z = pgdat->nr_zones - 1; z >= 0; z--) {
+		struct zone *zone = pgdat->node_zones + z;
+
+		if (!populated_zone(zone))
+			continue;
+
+		/* Avoid waking kswapd by allocating pages_to_migrate pages. */
+		if (!zone_watermark_ok(zone, 0,
+				       high_wmark_pages(zone) +
+				       nr_migrate_pages,
+				       0, 0))
+			continue;
+		return true;
+	}
+	return false;
+}
+
+static struct page *alloc_misplaced_dst_page(struct page *page,
+					   unsigned long data)
+{
+	int nid = (int) data;
+	struct page *newpage;
+
+	newpage = __alloc_pages_node(nid,
+					 (GFP_HIGHUSER_MOVABLE |
+					  __GFP_THISNODE | __GFP_NOMEMALLOC |
+					  __GFP_NORETRY | __GFP_NOWARN) &
+					 ~__GFP_RECLAIM, 0);
+
+	return newpage;
+}
+
+static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
+{
+	int page_lru;
+
+	VM_BUG_ON_PAGE(compound_order(page) && !PageTransHuge(page), page);
+
+	/* Avoid migrating to a node that is nearly full */
+	if (!migrate_balanced_pgdat(pgdat, 1UL << compound_order(page)))
+		return 0;
+
+	if (isolate_lru_page(page))
+		return 0;
+
+	/*
+	 * migrate_misplaced_transhuge_page() skips page migration's usual
+	 * check on page_count(), so we must do it here, now that the page
+	 * has been isolated: a GUP pin, or any other pin, prevents migration.
+	 * The expected page count is 3: 1 for page's mapcount and 1 for the
+	 * caller's pin and 1 for the reference taken by isolate_lru_page().
+	 */
+	if (PageTransHuge(page) && page_count(page) != 3) {
+		putback_lru_page(page);
+		return 0;
+	}
+
+	page_lru = page_is_file_cache(page);
+	mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON + page_lru,
+				hpage_nr_pages(page));
+
+	/*
+	 * Isolating the page has taken another reference, so the
+	 * caller's reference can be safely dropped without the page
+	 * disappearing underneath us during migration.
+	 */
+	put_page(page);
+	return 1;
+}
+
+bool pmd_trans_migrating(pmd_t pmd)
+{
+	struct page *page = pmd_page(pmd);
+	return PageLocked(page);
+}
+
+/*
+ * Attempt to migrate a misplaced page to the specified destination
+ * node. Caller is expected to have an elevated reference count on
+ * the page that will be dropped by this function before returning.
+ */
+int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
+			   int node)
+{
+	pg_data_t *pgdat = NODE_DATA(node);
+	int isolated;
+	int nr_remaining;
+	LIST_HEAD(migratepages);
+
+	/*
+	 * Don't migrate file pages that are mapped in multiple processes
+	 * with execute permissions as they are probably shared libraries.
+	 */
+	if (page_mapcount(page) != 1 && page_is_file_cache(page) &&
+	    (vma->vm_flags & VM_EXEC))
+		goto out;
+
+	/*
+	 * Also do not migrate dirty pages as not all filesystems can move
+	 * dirty pages in MIGRATE_ASYNC mode which is a waste of cycles.
+	 */
+	if (page_is_file_cache(page) && PageDirty(page))
+		goto out;
+
+	isolated = numamigrate_isolate_page(pgdat, page);
+	if (!isolated)
+		goto out;
+
+	list_add(&page->lru, &migratepages);
+	nr_remaining = migrate_pages(&migratepages, alloc_misplaced_dst_page,
+				     NULL, node, MIGRATE_ASYNC,
+				     MR_NUMA_MISPLACED);
+	if (nr_remaining) {
+		if (!list_empty(&migratepages)) {
+			list_del(&page->lru);
+			dec_node_page_state(page, NR_ISOLATED_ANON +
+					page_is_file_cache(page));
+			putback_lru_page(page);
+		}
+		isolated = 0;
+	} else
+		count_vm_numa_event(NUMA_PAGE_MIGRATE);
+	BUG_ON(!list_empty(&migratepages));
+	return isolated;
+
+out:
+	put_page(page);
+	return 0;
+}
+#endif /* CONFIG_NUMA_BALANCING */
+
+#if defined(CONFIG_NUMA_BALANCING) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
+/*
+ * Migrates a THP to a given target node. page must be locked and is unlocked
+ * before returning.
+ */
+int migrate_misplaced_transhuge_page(struct mm_struct *mm,
+				struct vm_area_struct *vma,
+				pmd_t *pmd, pmd_t entry,
+				unsigned long address,
+				struct page *page, int node)
+{
+	spinlock_t *ptl;
+	pg_data_t *pgdat = NODE_DATA(node);
+	int isolated = 0;
+	struct page *new_page = NULL;
+	int page_lru = page_is_file_cache(page);
+	unsigned long mmun_start = address & HPAGE_PMD_MASK;
+	unsigned long mmun_end = mmun_start + HPAGE_PMD_SIZE;
+
+	new_page = alloc_pages_node(node,
+		(GFP_TRANSHUGE_LIGHT | __GFP_THISNODE),
+		HPAGE_PMD_ORDER);
+	if (!new_page)
+		goto out_fail;
+	prep_transhuge_page(new_page);
+
+	isolated = numamigrate_isolate_page(pgdat, page);
+	if (!isolated) {
+		put_page(new_page);
+		goto out_fail;
+	}
+
+	/* Prepare a page as a migration target */
+	__SetPageLocked(new_page);
+	if (PageSwapBacked(page))
+		__SetPageSwapBacked(new_page);
+
+	/* anon mapping, we can simply copy page->mapping to the new page: */
+	new_page->mapping = page->mapping;
+	new_page->index = page->index;
+	migrate_page_copy(new_page, page);
+	WARN_ON(PageLRU(new_page));
+
+	/* Recheck the target PMD */
+	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
+	ptl = pmd_lock(mm, pmd);
+	if (unlikely(!pmd_same(*pmd, entry) || !page_ref_freeze(page, 2))) {
+		spin_unlock(ptl);
+		mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
+
+		/* Reverse changes made by migrate_page_copy() */
+		if (TestClearPageActive(new_page))
+			SetPageActive(page);
+		if (TestClearPageUnevictable(new_page))
+			SetPageUnevictable(page);
+
+		unlock_page(new_page);
+		put_page(new_page);		/* Free it */
+
+		/* Retake the callers reference and putback on LRU */
+		get_page(page);
+		putback_lru_page(page);
+		mod_node_page_state(page_pgdat(page),
+			 NR_ISOLATED_ANON + page_lru, -HPAGE_PMD_NR);
+
+		goto out_unlock;
+	}
+
+	entry = mk_huge_pmd(new_page, vma->vm_page_prot);
+	entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
+
+	/*
+	 * Overwrite the old entry under pagetable lock and establish
+	 * the new PTE. Any parallel GUP will either observe the old
+	 * page blocking on the page lock, block on the page table
+	 * lock or observe the new page. The SetPageUptodate on the
+	 * new page and page_add_new_anon_rmap guarantee the copy is
+	 * visible before the pagetable update.
+	 */
+	flush_cache_range(vma, mmun_start, mmun_end);
+	page_add_anon_rmap(new_page, vma, mmun_start, true);
+	/*
+	 * At this point the pmd is numa/protnone (i.e. non present) and the TLB
+	 * has already been flushed globally.  So no TLB can be currently
+	 * caching this non present pmd mapping.  There's no need to clear the
+	 * pmd before doing set_pmd_at(), nor to flush the TLB after
+	 * set_pmd_at().  Clearing the pmd here would introduce a race
+	 * condition against MADV_DONTNEED, because MADV_DONTNEED only holds the
+	 * mmap_sem for reading.  If the pmd is set to NULL at any given time,
+	 * MADV_DONTNEED won't wait on the pmd lock and it'll skip clearing this
+	 * pmd.
+	 */
+	set_pmd_at(mm, mmun_start, pmd, entry);
+	update_mmu_cache_pmd(vma, address, &entry);
+
+	page_ref_unfreeze(page, 2);
+	mlock_migrate_page(new_page, page);
+	page_remove_rmap(page, true);
+	set_page_owner_migrate_reason(new_page, MR_NUMA_MISPLACED);
+
+	spin_unlock(ptl);
+	/*
+	 * No need to double call mmu_notifier->invalidate_range() callback as
+	 * the above pmdp_huge_clear_flush_notify() did already call it.
+	 */
+	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
+
+	/* Take an "isolate" reference and put new page on the LRU. */
+	get_page(new_page);
+	putback_lru_page(new_page);
+
+	unlock_page(new_page);
+	unlock_page(page);
+	put_page(page);			/* Drop the rmap reference */
+	put_page(page);			/* Drop the LRU isolation reference */
+
+	count_vm_events(PGMIGRATE_SUCCESS, HPAGE_PMD_NR);
+	count_vm_numa_events(NUMA_PAGE_MIGRATE, HPAGE_PMD_NR);
+
+	mod_node_page_state(page_pgdat(page),
+			NR_ISOLATED_ANON + page_lru,
+			-HPAGE_PMD_NR);
+	return isolated;
+
+out_fail:
+	count_vm_events(PGMIGRATE_FAIL, HPAGE_PMD_NR);
+	ptl = pmd_lock(mm, pmd);
+	if (pmd_same(*pmd, entry)) {
+		entry = pmd_modify(entry, vma->vm_page_prot);
+		set_pmd_at(mm, mmun_start, pmd, entry);
+		update_mmu_cache_pmd(vma, address, &entry);
+	}
+	spin_unlock(ptl);
+
+out_unlock:
+	unlock_page(page);
+	put_page(page);
+	return 0;
+}
+#endif /* CONFIG_NUMA_BALANCING */
+
+#endif /* CONFIG_NUMA */
+
+#if defined(CONFIG_MIGRATE_VMA_HELPER)
+struct migrate_vma {
+	struct vm_area_struct	*vma;
+	unsigned long		*dst;
+	unsigned long		*src;
+	unsigned long		cpages;
+	unsigned long		npages;
+	unsigned long		start;
+	unsigned long		end;
+};
+
+static int migrate_vma_collect_hole(unsigned long start,
+				    unsigned long end,
+				    struct mm_walk *walk)
+{
+	struct migrate_vma *migrate = walk->private;
+	unsigned long addr;
+
+	for (addr = start & PAGE_MASK; addr < end; addr += PAGE_SIZE) {
+		migrate->src[migrate->npages] = MIGRATE_PFN_MIGRATE;
+		migrate->dst[migrate->npages] = 0;
+		migrate->npages++;
+		migrate->cpages++;
+	}
+
+	return 0;
+}
+
+static int migrate_vma_collect_skip(unsigned long start,
+				    unsigned long end,
+				    struct mm_walk *walk)
+{
+	struct migrate_vma *migrate = walk->private;
+	unsigned long addr;
+
+	for (addr = start & PAGE_MASK; addr < end; addr += PAGE_SIZE) {
+		migrate->dst[migrate->npages] = 0;
+		migrate->src[migrate->npages++] = 0;
+	}
+
+	return 0;
+}
+
+static int migrate_vma_collect_pmd(pmd_t *pmdp,
+				   unsigned long start,
+				   unsigned long end,
+				   struct mm_walk *walk)
+{
+	struct migrate_vma *migrate = walk->private;
+	struct vm_area_struct *vma = walk->vma;
+	struct mm_struct *mm = vma->vm_mm;
+	unsigned long addr = start, unmapped = 0;
+	spinlock_t *ptl;
+	pte_t *ptep;
+
+again:
+	if (pmd_none(*pmdp))
+		return migrate_vma_collect_hole(start, end, walk);
+
+	if (pmd_trans_huge(*pmdp)) {
+		struct page *page;
+
+		ptl = pmd_lock(mm, pmdp);
+		if (unlikely(!pmd_trans_huge(*pmdp))) {
+			spin_unlock(ptl);
+			goto again;
+		}
+
+		page = pmd_page(*pmdp);
+		if (is_huge_zero_page(page)) {
+			spin_unlock(ptl);
+			split_huge_pmd(vma, pmdp, addr);
+			if (pmd_trans_unstable(pmdp))
+				return migrate_vma_collect_skip(start, end,
+								walk);
+		} else {
+			int ret;
+
+			get_page(page);
+			spin_unlock(ptl);
+			if (unlikely(!trylock_page(page)))
+				return migrate_vma_collect_skip(start, end,
+								walk);
+			ret = split_huge_page(page);
+			unlock_page(page);
+			put_page(page);
+			if (ret)
+				return migrate_vma_collect_skip(start, end,
+								walk);
+			if (pmd_none(*pmdp))
+				return migrate_vma_collect_hole(start, end,
+								walk);
+		}
+	}
+
+	if (unlikely(pmd_bad(*pmdp)))
+		return migrate_vma_collect_skip(start, end, walk);
+
+	ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
+	arch_enter_lazy_mmu_mode();
+
+	for (; addr < end; addr += PAGE_SIZE, ptep++) {
+		unsigned long mpfn, pfn;
+		struct page *page;
+		swp_entry_t entry;
+		pte_t pte;
+
+		pte = *ptep;
+		pfn = pte_pfn(pte);
+
+		if (pte_none(pte)) {
+			mpfn = MIGRATE_PFN_MIGRATE;
+			migrate->cpages++;
+			pfn = 0;
+			goto next;
+		}
+
+		if (!pte_present(pte)) {
+			mpfn = pfn = 0;
+
+			/*
+			 * Only care about unaddressable device page special
+			 * page table entry. Other special swap entries are not
+			 * migratable, and we ignore regular swapped page.
+			 */
+			entry = pte_to_swp_entry(pte);
+			if (!is_device_private_entry(entry))
+				goto next;
+
+			page = device_private_entry_to_page(entry);
+			mpfn = migrate_pfn(page_to_pfn(page))|
+				MIGRATE_PFN_DEVICE | MIGRATE_PFN_MIGRATE;
+			if (is_write_device_private_entry(entry))
+				mpfn |= MIGRATE_PFN_WRITE;
+		} else {
+			if (is_zero_pfn(pfn)) {
+				mpfn = MIGRATE_PFN_MIGRATE;
+				migrate->cpages++;
+				pfn = 0;
+				goto next;
+			}
+			page = _vm_normal_page(migrate->vma, addr, pte, true);
+			mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
+			mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
+		}
+
+		/* FIXME support THP */
+		if (!page || !page->mapping || PageTransCompound(page)) {
+			mpfn = pfn = 0;
+			goto next;
+		}
+		pfn = page_to_pfn(page);
+
+		/*
+		 * By getting a reference on the page we pin it and that blocks
+		 * any kind of migration. Side effect is that it "freezes" the
+		 * pte.
+		 *
+		 * We drop this reference after isolating the page from the lru
+		 * for non device page (device page are not on the lru and thus
+		 * can't be dropped from it).
+		 */
+		get_page(page);
+		migrate->cpages++;
+
+		/*
+		 * Optimize for the common case where page is only mapped once
+		 * in one process. If we can lock the page, then we can safely
+		 * set up a special migration page table entry now.
+		 */
+		if (trylock_page(page)) {
+			pte_t swp_pte;
+
+			mpfn |= MIGRATE_PFN_LOCKED;
+			ptep_get_and_clear(mm, addr, ptep);
+
+			/* Setup special migration page table entry */
+			entry = make_migration_entry(page, mpfn &
+						     MIGRATE_PFN_WRITE);
+			swp_pte = swp_entry_to_pte(entry);
+			if (pte_soft_dirty(pte))
+				swp_pte = pte_swp_mksoft_dirty(swp_pte);
+			set_pte_at(mm, addr, ptep, swp_pte);
+
+			/*
+			 * This is like regular unmap: we remove the rmap and
+			 * drop page refcount. Page won't be freed, as we took
+			 * a reference just above.
+			 */
+			page_remove_rmap(page, false);
+			put_page(page);
+
+			if (pte_present(pte))
+				unmapped++;
+		}
+
+next:
+		migrate->dst[migrate->npages] = 0;
+		migrate->src[migrate->npages++] = mpfn;
+	}
+	arch_leave_lazy_mmu_mode();
+	pte_unmap_unlock(ptep - 1, ptl);
+
+	/* Only flush the TLB if we actually modified any entries */
+	if (unmapped)
+		flush_tlb_range(walk->vma, start, end);
+
+	return 0;
+}
+
+/*
+ * migrate_vma_collect() - collect pages over a range of virtual addresses
+ * @migrate: migrate struct containing all migration information
+ *
+ * This will walk the CPU page table. For each virtual address backed by a
+ * valid page, it updates the src array and takes a reference on the page, in
+ * order to pin the page until we lock it and unmap it.
+ */
+static void migrate_vma_collect(struct migrate_vma *migrate)
+{
+	struct mm_walk mm_walk = {
+		.pmd_entry = migrate_vma_collect_pmd,
+		.pte_hole = migrate_vma_collect_hole,
+		.vma = migrate->vma,
+		.mm = migrate->vma->vm_mm,
+		.private = migrate,
+	};
+
+	mmu_notifier_invalidate_range_start(mm_walk.mm,
+					    migrate->start,
+					    migrate->end);
+	walk_page_range(migrate->start, migrate->end, &mm_walk);
+	mmu_notifier_invalidate_range_end(mm_walk.mm,
+					  migrate->start,
+					  migrate->end);
+
+	migrate->end = migrate->start + (migrate->npages << PAGE_SHIFT);
+}
+
+/*
+ * migrate_vma_check_page() - check if page is pinned or not
+ * @page: struct page to check
+ *
+ * Pinned pages cannot be migrated. This is the same test as in
+ * migrate_page_move_mapping(), except that here we allow migration of a
+ * ZONE_DEVICE page.
+ */
+static bool migrate_vma_check_page(struct page *page)
+{
+	/*
+	 * One extra ref because caller holds an extra reference, either from
+	 * isolate_lru_page() for a regular page, or migrate_vma_collect() for
+	 * a device page.
+	 */
+	int extra = 1;
+
+	/*
+	 * FIXME support THP (transparent huge page), it is bit more complex to
+	 * check them than regular pages, because they can be mapped with a pmd
+	 * or with a pte (split pte mapping).
+	 */
+	if (PageCompound(page))
+		return false;
+
+	/* Page from ZONE_DEVICE have one extra reference */
+	if (is_zone_device_page(page)) {
+		/*
+		 * Private page can never be pin as they have no valid pte and
+		 * GUP will fail for those. Yet if there is a pending migration
+		 * a thread might try to wait on the pte migration entry and
+		 * will bump the page reference count. Sadly there is no way to
+		 * differentiate a regular pin from migration wait. Hence to
+		 * avoid 2 racing thread trying to migrate back to CPU to enter
+		 * infinite loop (one stoping migration because the other is
+		 * waiting on pte migration entry). We always return true here.
+		 *
+		 * FIXME proper solution is to rework migration_entry_wait() so
+		 * it does not need to take a reference on page.
+		 */
+		if (is_device_private_page(page))
+			return true;
+
+		/*
+		 * Only allow device public page to be migrated and account for
+		 * the extra reference count imply by ZONE_DEVICE pages.
+		 */
+		if (!is_device_public_page(page))
+			return false;
+		extra++;
+	}
+
+	/* For file back page */
+	if (page_mapping(page))
+		extra += 1 + page_has_private(page);
+
+	if ((page_count(page) - extra) > page_mapcount(page))
+		return false;
+
+	return true;
+}
+
+/*
+ * migrate_vma_prepare() - lock pages and isolate them from the lru
+ * @migrate: migrate struct containing all migration information
+ *
+ * This locks pages that have been collected by migrate_vma_collect(). Once each
+ * page is locked it is isolated from the lru (for non-device pages). Finally,
+ * the ref taken by migrate_vma_collect() is dropped, as locked pages cannot be
+ * migrated by concurrent kernel threads.
+ */
+static void migrate_vma_prepare(struct migrate_vma *migrate)
+{
+	const unsigned long npages = migrate->npages;
+	const unsigned long start = migrate->start;
+	unsigned long addr, i, restore = 0;
+	bool allow_drain = true;
+
+	lru_add_drain();
+
+	for (i = 0; (i < npages) && migrate->cpages; i++) {
+		struct page *page = migrate_pfn_to_page(migrate->src[i]);
+		bool remap = true;
+
+		if (!page)
+			continue;
+
+		if (!(migrate->src[i] & MIGRATE_PFN_LOCKED)) {
+			/*
+			 * Because we are migrating several pages there can be
+			 * a deadlock between 2 concurrent migration where each
+			 * are waiting on each other page lock.
+			 *
+			 * Make migrate_vma() a best effort thing and backoff
+			 * for any page we can not lock right away.
+			 */
+			if (!trylock_page(page)) {
+				migrate->src[i] = 0;
+				migrate->cpages--;
+				put_page(page);
+				continue;
+			}
+			remap = false;
+			migrate->src[i] |= MIGRATE_PFN_LOCKED;
+		}
+
+		/* ZONE_DEVICE pages are not on LRU */
+		if (!is_zone_device_page(page)) {
+			if (!PageLRU(page) && allow_drain) {
+				/* Drain CPU's pagevec */
+				lru_add_drain_all();
+				allow_drain = false;
+			}
+
+			if (isolate_lru_page(page)) {
+				if (remap) {
+					migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
+					migrate->cpages--;
+					restore++;
+				} else {
+					migrate->src[i] = 0;
+					unlock_page(page);
+					migrate->cpages--;
+					put_page(page);
+				}
+				continue;
+			}
+
+			/* Drop the reference we took in collect */
+			put_page(page);
+		}
+
+		if (!migrate_vma_check_page(page)) {
+			if (remap) {
+				migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
+				migrate->cpages--;
+				restore++;
+
+				if (!is_zone_device_page(page)) {
+					get_page(page);
+					putback_lru_page(page);
+				}
+			} else {
+				migrate->src[i] = 0;
+				unlock_page(page);
+				migrate->cpages--;
+
+				if (!is_zone_device_page(page))
+					putback_lru_page(page);
+				else
+					put_page(page);
+			}
+		}
+	}
+
+	for (i = 0, addr = start; i < npages && restore; i++, addr += PAGE_SIZE) {
+		struct page *page = migrate_pfn_to_page(migrate->src[i]);
+
+		if (!page || (migrate->src[i] & MIGRATE_PFN_MIGRATE))
+			continue;
+
+		remove_migration_pte(page, migrate->vma, addr, page);
+
+		migrate->src[i] = 0;
+		unlock_page(page);
+		put_page(page);
+		restore--;
+	}
+}
+
+/*
+ * migrate_vma_unmap() - replace page mapping with special migration pte entry
+ * @migrate: migrate struct containing all migration information
+ *
+ * Replace page mapping (CPU page table pte) with a special migration pte entry
+ * and check again if it has been pinned. Pinned pages are restored because we
+ * cannot migrate them.
+ *
+ * This is the last step before we call the device driver callback to allocate
+ * destination memory and copy contents of original page over to new page.
+ */
+static void migrate_vma_unmap(struct migrate_vma *migrate)
+{
+	int flags = TTU_MIGRATION | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS;
+	const unsigned long npages = migrate->npages;
+	const unsigned long start = migrate->start;
+	unsigned long addr, i, restore = 0;
+
+	for (i = 0; i < npages; i++) {
+		struct page *page = migrate_pfn_to_page(migrate->src[i]);
+
+		if (!page || !(migrate->src[i] & MIGRATE_PFN_MIGRATE))
+			continue;
+
+		if (page_mapped(page)) {
+			try_to_unmap(page, flags);
+			if (page_mapped(page))
+				goto restore;
+		}
+
+		if (migrate_vma_check_page(page))
+			continue;
+
+restore:
+		migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
+		migrate->cpages--;
+		restore++;
+	}
+
+	for (addr = start, i = 0; i < npages && restore; addr += PAGE_SIZE, i++) {
+		struct page *page = migrate_pfn_to_page(migrate->src[i]);
+
+		if (!page || (migrate->src[i] & MIGRATE_PFN_MIGRATE))
+			continue;
+
+		remove_migration_ptes(page, page, false);
+
+		migrate->src[i] = 0;
+		unlock_page(page);
+		restore--;
+
+		if (is_zone_device_page(page))
+			put_page(page);
+		else
+			putback_lru_page(page);
+	}
+}
+
+static void migrate_vma_insert_page(struct migrate_vma *migrate,
+				    unsigned long addr,
+				    struct page *page,
+				    unsigned long *src,
+				    unsigned long *dst)
+{
+	struct vm_area_struct *vma = migrate->vma;
+	struct mm_struct *mm = vma->vm_mm;
+	struct mem_cgroup *memcg;
+	bool flush = false;
+	spinlock_t *ptl;
+	pte_t entry;
+	pgd_t *pgdp;
+	p4d_t *p4dp;
+	pud_t *pudp;
+	pmd_t *pmdp;
+	pte_t *ptep;
+
+	/* Only allow populating anonymous memory */
+	if (!vma_is_anonymous(vma))
+		goto abort;
+
+	pgdp = pgd_offset(mm, addr);
+	p4dp = p4d_alloc(mm, pgdp, addr);
+	if (!p4dp)
+		goto abort;
+	pudp = pud_alloc(mm, p4dp, addr);
+	if (!pudp)
+		goto abort;
+	pmdp = pmd_alloc(mm, pudp, addr);
+	if (!pmdp)
+		goto abort;
+
+	if (pmd_trans_huge(*pmdp) || pmd_devmap(*pmdp))
+		goto abort;
+
+	/*
+	 * Use pte_alloc() instead of pte_alloc_map().  We can't run
+	 * pte_offset_map() on pmds where a huge pmd might be created
+	 * from a different thread.
+	 *
+	 * pte_alloc_map() is safe to use under down_write(mmap_sem) or when
+	 * parallel threads are excluded by other means.
+	 *
+	 * Here we only have down_read(mmap_sem).
+	 */
+	if (pte_alloc(mm, pmdp, addr))
+		goto abort;
+
+	/* See the comment in pte_alloc_one_map() */
+	if (unlikely(pmd_trans_unstable(pmdp)))
+		goto abort;
+
+	if (unlikely(anon_vma_prepare(vma)))
+		goto abort;
+	if (mem_cgroup_try_charge(page, vma->vm_mm, GFP_KERNEL, &memcg, false))
+		goto abort;
+
+	/*
+	 * The memory barrier inside __SetPageUptodate makes sure that
+	 * preceding stores to the page contents become visible before
+	 * the set_pte_at() write.
+	 */
+	__SetPageUptodate(page);
+
+	if (is_zone_device_page(page)) {
+		if (is_device_private_page(page)) {
+			swp_entry_t swp_entry;
+
+			swp_entry = make_device_private_entry(page, vma->vm_flags & VM_WRITE);
+			entry = swp_entry_to_pte(swp_entry);
+		} else if (is_device_public_page(page)) {
+			entry = pte_mkold(mk_pte(page, READ_ONCE(vma->vm_page_prot)));
+			if (vma->vm_flags & VM_WRITE)
+				entry = pte_mkwrite(pte_mkdirty(entry));
+			entry = pte_mkdevmap(entry);
+		}
+	} else {
+		entry = mk_pte(page, vma->vm_page_prot);
+		if (vma->vm_flags & VM_WRITE)
+			entry = pte_mkwrite(pte_mkdirty(entry));
+	}
+
+	ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
+
+	if (pte_present(*ptep)) {
+		unsigned long pfn = pte_pfn(*ptep);
+
+		if (!is_zero_pfn(pfn)) {
+			pte_unmap_unlock(ptep, ptl);
+			mem_cgroup_cancel_charge(page, memcg, false);
+			goto abort;
+		}
+		flush = true;
+	} else if (!pte_none(*ptep)) {
+		pte_unmap_unlock(ptep, ptl);
+		mem_cgroup_cancel_charge(page, memcg, false);
+		goto abort;
+	}
+
+	/*
+	 * Check for usefaultfd but do not deliver the fault. Instead,
+	 * just back off.
+	 */
+	if (userfaultfd_missing(vma)) {
+		pte_unmap_unlock(ptep, ptl);
+		mem_cgroup_cancel_charge(page, memcg, false);
+		goto abort;
+	}
+
+	inc_mm_counter(mm, MM_ANONPAGES);
+	page_add_new_anon_rmap(page, vma, addr, false);
+	mem_cgroup_commit_charge(page, memcg, false, false);
+	if (!is_zone_device_page(page))
+		lru_cache_add_active_or_unevictable(page, vma);
+	get_page(page);
+
+	if (flush) {
+		flush_cache_page(vma, addr, pte_pfn(*ptep));
+		ptep_clear_flush_notify(vma, addr, ptep);
+		set_pte_at_notify(mm, addr, ptep, entry);
+		update_mmu_cache(vma, addr, ptep);
+	} else {
+		/* No need to invalidate - it was non-present before */
+		set_pte_at(mm, addr, ptep, entry);
+		update_mmu_cache(vma, addr, ptep);
+	}
+
+	pte_unmap_unlock(ptep, ptl);
+	*src = MIGRATE_PFN_MIGRATE;
+	return;
+
+abort:
+	*src &= ~MIGRATE_PFN_MIGRATE;
+}
+
+/*
+ * migrate_vma_pages() - migrate meta-data from src page to dst page
+ * @migrate: migrate struct containing all migration information
+ *
+ * This migrates struct page meta-data from source struct page to destination
+ * struct page. This effectively finishes the migration from source page to the
+ * destination page.
+ */
+static void migrate_vma_pages(struct migrate_vma *migrate)
+{
+	const unsigned long npages = migrate->npages;
+	const unsigned long start = migrate->start;
+	struct vm_area_struct *vma = migrate->vma;
+	struct mm_struct *mm = vma->vm_mm;
+	unsigned long addr, i, mmu_start;
+	bool notified = false;
+
+	for (i = 0, addr = start; i < npages; addr += PAGE_SIZE, i++) {
+		struct page *newpage = migrate_pfn_to_page(migrate->dst[i]);
+		struct page *page = migrate_pfn_to_page(migrate->src[i]);
+		struct address_space *mapping;
+		int r;
+
+		if (!newpage) {
+			migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
+			continue;
+		}
+
+		if (!page) {
+			if (!(migrate->src[i] & MIGRATE_PFN_MIGRATE)) {
+				continue;
+			}
+			if (!notified) {
+				mmu_start = addr;
+				notified = true;
+				mmu_notifier_invalidate_range_start(mm,
+								mmu_start,
+								migrate->end);
+			}
+			migrate_vma_insert_page(migrate, addr, newpage,
+						&migrate->src[i],
+						&migrate->dst[i]);
+			continue;
+		}
+
+		mapping = page_mapping(page);
+
+		if (is_zone_device_page(newpage)) {
+			if (is_device_private_page(newpage)) {
+				/*
+				 * For now only support private anonymous when
+				 * migrating to un-addressable device memory.
+				 */
+				if (mapping) {
+					migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
+					continue;
+				}
+			} else if (!is_device_public_page(newpage)) {
+				/*
+				 * Other types of ZONE_DEVICE page are not
+				 * supported.
+				 */
+				migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
+				continue;
+			}
+		}
+
+		r = migrate_page(mapping, newpage, page, MIGRATE_SYNC_NO_COPY);
+		if (r != MIGRATEPAGE_SUCCESS)
+			migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
+	}
+
+	/*
+	 * No need to double call mmu_notifier->invalidate_range() callback as
+	 * the above ptep_clear_flush_notify() inside migrate_vma_insert_page()
+	 * did already call it.
+	 */
+	if (notified)
+		mmu_notifier_invalidate_range_only_end(mm, mmu_start,
+						       migrate->end);
+}
+
+/*
+ * migrate_vma_finalize() - restore CPU page table entry
+ * @migrate: migrate struct containing all migration information
+ *
+ * This replaces the special migration pte entry with either a mapping to the
+ * new page if migration was successful for that page, or to the original page
+ * otherwise.
+ *
+ * This also unlocks the pages and puts them back on the lru, or drops the extra
+ * refcount, for device pages.
+ */
+static void migrate_vma_finalize(struct migrate_vma *migrate)
+{
+	const unsigned long npages = migrate->npages;
+	unsigned long i;
+
+	for (i = 0; i < npages; i++) {
+		struct page *newpage = migrate_pfn_to_page(migrate->dst[i]);
+		struct page *page = migrate_pfn_to_page(migrate->src[i]);
+
+		if (!page) {
+			if (newpage) {
+				unlock_page(newpage);
+				put_page(newpage);
+			}
+			continue;
+		}
+
+		if (!(migrate->src[i] & MIGRATE_PFN_MIGRATE) || !newpage) {
+			if (newpage) {
+				unlock_page(newpage);
+				put_page(newpage);
+			}
+			newpage = page;
+		}
+
+		remove_migration_ptes(page, newpage, false);
+		unlock_page(page);
+		migrate->cpages--;
+
+		if (is_zone_device_page(page))
+			put_page(page);
+		else
+			putback_lru_page(page);
+
+		if (newpage != page) {
+			unlock_page(newpage);
+			if (is_zone_device_page(newpage))
+				put_page(newpage);
+			else
+				putback_lru_page(newpage);
+		}
+	}
+}
+
+/*
+ * migrate_vma() - migrate a range of memory inside vma
+ *
+ * @ops: migration callback for allocating destination memory and copying
+ * @vma: virtual memory area containing the range to be migrated
+ * @start: start address of the range to migrate (inclusive)
+ * @end: end address of the range to migrate (exclusive)
+ * @src: array of hmm_pfn_t containing source pfns
+ * @dst: array of hmm_pfn_t containing destination pfns
+ * @private: pointer passed back to each of the callback
+ * Returns: 0 on success, error code otherwise
+ *
+ * This function tries to migrate a range of memory virtual address range, using
+ * callbacks to allocate and copy memory from source to destination. First it
+ * collects all the pages backing each virtual address in the range, saving this
+ * inside the src array. Then it locks those pages and unmaps them. Once the pages
+ * are locked and unmapped, it checks whether each page is pinned or not. Pages
+ * that aren't pinned have the MIGRATE_PFN_MIGRATE flag set (by this function)
+ * in the corresponding src array entry. It then restores any pages that are
+ * pinned, by remapping and unlocking those pages.
+ *
+ * At this point it calls the alloc_and_copy() callback. For documentation on
+ * what is expected from that callback, see struct migrate_vma_ops comments in
+ * include/linux/migrate.h
+ *
+ * After the alloc_and_copy() callback, this function goes over each entry in
+ * the src array that has the MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag
+ * set. If the corresponding entry in dst array has MIGRATE_PFN_VALID flag set,
+ * then the function tries to migrate struct page information from the source
+ * struct page to the destination struct page. If it fails to migrate the struct
+ * page information, then it clears the MIGRATE_PFN_MIGRATE flag in the src
+ * array.
+ *
+ * At this point all successfully migrated pages have an entry in the src
+ * array with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag set and the dst
+ * array entry with MIGRATE_PFN_VALID flag set.
+ *
+ * It then calls the finalize_and_map() callback. See comments for "struct
+ * migrate_vma_ops", in include/linux/migrate.h for details about
+ * finalize_and_map() behavior.
+ *
+ * After the finalize_and_map() callback, for successfully migrated pages, this
+ * function updates the CPU page table to point to new pages, otherwise it
+ * restores the CPU page table to point to the original source pages.
+ *
+ * Function returns 0 after the above steps, even if no pages were migrated
+ * (The function only returns an error if any of the arguments are invalid.)
+ *
+ * Both src and dst array must be big enough for (end - start) >> PAGE_SHIFT
+ * unsigned long entries.
+ */
+int migrate_vma(const struct migrate_vma_ops *ops,
+		struct vm_area_struct *vma,
+		unsigned long start,
+		unsigned long end,
+		unsigned long *src,
+		unsigned long *dst,
+		void *private)
+{
+	struct migrate_vma migrate;
+
+	/* Sanity check the arguments */
+	start &= PAGE_MASK;
+	end &= PAGE_MASK;
+	if (!vma || is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL) ||
+			vma_is_dax(vma))
+		return -EINVAL;
+	if (start < vma->vm_start || start >= vma->vm_end)
+		return -EINVAL;
+	if (end <= vma->vm_start || end > vma->vm_end)
+		return -EINVAL;
+	if (!ops || !src || !dst || start >= end)
+		return -EINVAL;
+
+	memset(src, 0, sizeof(*src) * ((end - start) >> PAGE_SHIFT));
+	migrate.src = src;
+	migrate.dst = dst;
+	migrate.start = start;
+	migrate.npages = 0;
+	migrate.cpages = 0;
+	migrate.end = end;
+	migrate.vma = vma;
+
+	/* Collect, and try to unmap source pages */
+	migrate_vma_collect(&migrate);
+	if (!migrate.cpages)
+		return 0;
+
+	/* Lock and isolate page */
+	migrate_vma_prepare(&migrate);
+	if (!migrate.cpages)
+		return 0;
+
+	/* Unmap pages */
+	migrate_vma_unmap(&migrate);
+	if (!migrate.cpages)
+		return 0;
+
+	/*
+	 * At this point pages are locked and unmapped, and thus they have
+	 * stable content and can safely be copied to destination memory that
+	 * is allocated by the callback.
+	 *
+	 * Note that migration can fail in migrate_vma_struct_page() for each
+	 * individual page.
+	 */
+	ops->alloc_and_copy(vma, src, dst, start, end, private);
+
+	/* This does the real migration of struct page */
+	migrate_vma_pages(&migrate);
+
+	ops->finalize_and_map(vma, src, dst, start, end, private);
+
+	/* Unlock and remap pages */
+	migrate_vma_finalize(&migrate);
+
+	return 0;
+}
+EXPORT_SYMBOL(migrate_vma);
+#endif /* defined(MIGRATE_VMA_HELPER) */