[PATCH v3 3/6] mm: support THP migration to device private memory

[Ralph Campbell <rcampbell@nvidia.com>]

Support transparent huge page migration to ZONE_DEVICE private memory.
A new selection flag (MIGRATE_VMA_SELECT_COMPOUND) is added to request
THP migration. Otherwise, THPs are split when filling in the source PFN
array. A new flag (MIGRATE_PFN_COMPOUND) is added to the source PFN array
to indicate a huge page can be migrated. If the device driver can allocate
a huge page, it sets the MIGRATE_PFN_COMPOUND flag in the destination PFN
array. migrate_vma_pages() will fallback to PAGE_SIZE pages if
MIGRATE_PFN_COMPOUND is not set in both source and destination arrays.

Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
---
 include/linux/huge_mm.h  |   7 +
 include/linux/memremap.h |   9 +
 include/linux/migrate.h  |   2 +
 mm/huge_memory.c         | 124 +++++++++---
 mm/memcontrol.c          |  25 ++-
 mm/memory.c              |  10 +-
 mm/memremap.c            |   4 +-
 mm/migrate.c             | 413 ++++++++++++++++++++++++++++++++-------
 mm/rmap.c                |   2 +-
 9 files changed, 486 insertions(+), 110 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 3ec26ef27a93..1e8625cc233c 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -190,6 +190,8 @@ bool is_transparent_hugepage(struct page *page);
 
 bool can_split_huge_page(struct page *page, int *pextra_pins);
 int split_huge_page_to_list(struct page *page, struct list_head *list);
+int split_migrating_huge_page(struct vm_area_struct *vma, pmd_t *pmd,
+			      unsigned long address, struct page *page);
 static inline int split_huge_page(struct page *page)
 {
 	return split_huge_page_to_list(page, NULL);
@@ -456,6 +458,11 @@ static inline bool is_huge_zero_page(struct page *page)
 	return false;
 }
 
+static inline bool is_huge_zero_pmd(pmd_t pmd)
+{
+	return false;
+}
+
 static inline bool is_huge_zero_pud(pud_t pud)
 {
 	return false;
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 86c6c368ce9b..9b39a896af37 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -87,6 +87,15 @@ struct dev_pagemap_ops {
 	 * the page back to a CPU accessible page.
 	 */
 	vm_fault_t (*migrate_to_ram)(struct vm_fault *vmf);
+
+	/*
+	 * Used for private (un-addressable) device memory only.
+	 * This is called when a compound device private page is split.
+	 * The driver uses this callback to set tail_page->pgmap and
+	 * tail_page->zone_device_data appropriately based on the head
+	 * page.
+	 */
+	void (*page_split)(struct page *head, struct page *tail_page);
 };
 
 #define PGMAP_ALTMAP_VALID	(1 << 0)
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 0f8d1583fa8e..92179bf360d1 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -144,6 +144,7 @@ static inline int migrate_misplaced_transhuge_page(struct mm_struct *mm,
 #define MIGRATE_PFN_MIGRATE	(1UL << 1)
 #define MIGRATE_PFN_LOCKED	(1UL << 2)
 #define MIGRATE_PFN_WRITE	(1UL << 3)
+#define MIGRATE_PFN_COMPOUND	(1UL << 4)
 #define MIGRATE_PFN_SHIFT	6
 
 static inline struct page *migrate_pfn_to_page(unsigned long mpfn)
@@ -161,6 +162,7 @@ static inline unsigned long migrate_pfn(unsigned long pfn)
 enum migrate_vma_direction {
 	MIGRATE_VMA_SELECT_SYSTEM = 1 << 0,
 	MIGRATE_VMA_SELECT_DEVICE_PRIVATE = 1 << 1,
+	MIGRATE_VMA_SELECT_COMPOUND = 1 << 2,
 };
 
 struct migrate_vma {
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index b4141f12ff31..a073e66d0ee2 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1682,23 +1682,35 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 	} else {
 		struct page *page = NULL;
 		int flush_needed = 1;
+		bool is_anon = false;
 
 		if (pmd_present(orig_pmd)) {
 			page = pmd_page(orig_pmd);
+			is_anon = PageAnon(page);
 			page_remove_rmap(page, true);
 			VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
 			VM_BUG_ON_PAGE(!PageHead(page), page);
 		} else if (thp_migration_supported()) {
 			swp_entry_t entry;
 
-			VM_BUG_ON(!is_pmd_migration_entry(orig_pmd));
 			entry = pmd_to_swp_entry(orig_pmd);
-			page = pfn_to_page(swp_offset(entry));
+			if (is_device_private_entry(entry)) {
+				page = device_private_entry_to_page(entry);
+				is_anon = PageAnon(page);
+				page_remove_rmap(page, true);
+				VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
+				VM_BUG_ON_PAGE(!PageHead(page), page);
+				put_page(page);
+			} else {
+				VM_BUG_ON(!is_pmd_migration_entry(orig_pmd));
+				page = pfn_to_page(swp_offset(entry));
+				is_anon = PageAnon(page);
+			}
 			flush_needed = 0;
 		} else
 			WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
 
-		if (PageAnon(page)) {
+		if (is_anon) {
 			zap_deposited_table(tlb->mm, pmd);
 			add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
 		} else {
@@ -2358,9 +2370,10 @@ static void remap_page(struct page *page, unsigned int nr)
 }
 
 static void __split_huge_page_tail(struct page *head, int tail,
-		struct lruvec *lruvec, struct list_head *list)
+		struct lruvec *lruvec, struct list_head *list, bool remap)
 {
 	struct page *page_tail = head + tail;
+	int pin_count;
 
 	VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail);
 
@@ -2396,15 +2409,24 @@ static void __split_huge_page_tail(struct page *head, int tail,
 	smp_wmb();
 
 	/*
-	 * Clear PageTail before unfreezing page refcount.
+	 * A successful get_page_unless_zero() might follow page_ref_unfreeze()
+	 * so PageTail needs to be cleared before unfreezing the page refcount
+	 * in order for compound_head() to work correctly.
 	 *
-	 * After successful get_page_unless_zero() might follow put_page()
-	 * which needs correct compound_head().
+	 * Also, ZONE_DEVICE struct pages share the compound_head field and
+	 * need to restore the pgmap pointer before unfreezing page refcount
+	 * in order for is_zone_device_page() to work correctly.
 	 */
-	clear_compound_head(page_tail);
+	if (is_device_private_page(head)) {
+		head->pgmap->ops->page_split(head, page_tail);
+		pin_count = 2;
+	} else {
+		clear_compound_head(page_tail);
+		pin_count = 1;
+	}
 
 	/* Finally unfreeze refcount. Additional reference from page cache. */
-	page_ref_unfreeze(page_tail, 1 + (!PageAnon(head) ||
+	page_ref_unfreeze(page_tail, pin_count + (!PageAnon(head) ||
 					  PageSwapCache(head)));
 
 	if (page_is_young(head))
@@ -2419,11 +2441,12 @@ static void __split_huge_page_tail(struct page *head, int tail,
 	 * pages to show after the currently processed elements - e.g.
 	 * migrate_pages
 	 */
-	lru_add_page_tail(head, page_tail, lruvec, list);
+	if (remap)
+		lru_add_page_tail(head, page_tail, lruvec, list);
 }
 
 static void __split_huge_page(struct page *page, struct list_head *list,
-		pgoff_t end, unsigned long flags)
+		pgoff_t end, unsigned long flags, bool remap)
 {
 	struct page *head = compound_head(page);
 	pg_data_t *pgdat = page_pgdat(head);
@@ -2447,7 +2470,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
 	}
 
 	for (i = nr - 1; i >= 1; i--) {
-		__split_huge_page_tail(head, i, lruvec, list);
+		__split_huge_page_tail(head, i, lruvec, list, remap);
 		/* Some pages can be beyond i_size: drop them from page cache */
 		if (head[i].index >= end) {
 			ClearPageDirty(head + i);
@@ -2474,6 +2497,9 @@ static void __split_huge_page(struct page *page, struct list_head *list,
 		if (PageSwapCache(head)) {
 			page_ref_add(head, 2);
 			xa_unlock(&swap_cache->i_pages);
+		} else if (is_device_private_page(head)) {
+			percpu_ref_get_many(page->pgmap->ref, nr - 1);
+			page_ref_add(head, 2);
 		} else {
 			page_ref_inc(head);
 		}
@@ -2485,6 +2511,9 @@ static void __split_huge_page(struct page *page, struct list_head *list,
 
 	spin_unlock_irqrestore(&pgdat->lru_lock, flags);
 
+	if (!remap)
+		return;
+
 	remap_page(head, nr);
 
 	if (PageSwapCache(head)) {
@@ -2602,6 +2631,7 @@ bool can_split_huge_page(struct page *page, int *pextra_pins)
 		extra_pins = PageSwapCache(page) ? thp_nr_pages(page) : 0;
 	else
 		extra_pins = thp_nr_pages(page);
+	extra_pins += is_device_private_page(page);
 	if (pextra_pins)
 		*pextra_pins = extra_pins;
 	return total_mapcount(page) == page_count(page) - extra_pins - 1;
@@ -2626,7 +2656,8 @@ bool can_split_huge_page(struct page *page, int *pextra_pins)
  * Returns -EBUSY if the page is pinned or if anon_vma disappeared from under
  * us.
  */
-int split_huge_page_to_list(struct page *page, struct list_head *list)
+static int __split_huge_page_to_list(struct page *page, struct list_head *list,
+				     bool remap)
 {
 	struct page *head = compound_head(page);
 	struct pglist_data *pgdata = NODE_DATA(page_to_nid(head));
@@ -2653,14 +2684,16 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 		 * is taken to serialise against parallel split or collapse
 		 * operations.
 		 */
-		anon_vma = page_get_anon_vma(head);
-		if (!anon_vma) {
-			ret = -EBUSY;
-			goto out;
+		if (remap) {
+			anon_vma = page_get_anon_vma(head);
+			if (!anon_vma) {
+				ret = -EBUSY;
+				goto out;
+			}
+			anon_vma_lock_write(anon_vma);
 		}
 		end = -1;
 		mapping = NULL;
-		anon_vma_lock_write(anon_vma);
 	} else {
 		mapping = head->mapping;
 
@@ -2686,13 +2719,19 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 	/*
 	 * Racy check if we can split the page, before unmap_page() will
 	 * split PMDs
+	 * If we are splitting a migrating THP, there is no check needed
+	 * because the page is already unmapped and isolated from the LRU.
 	 */
-	if (!can_split_huge_page(head, &extra_pins)) {
+	if (!remap)
+		extra_pins = thp_nr_pages(page) - 1 +
+			is_device_private_page(head);
+	else if (!can_split_huge_page(head, &extra_pins)) {
 		ret = -EBUSY;
 		goto out_unlock;
 	}
 
-	unmap_page(head);
+	if (remap)
+		unmap_page(head);
 	VM_BUG_ON_PAGE(compound_mapcount(head), head);
 
 	/* prevent PageLRU to go away from under us, and freeze lru stats */
@@ -2717,7 +2756,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 	if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) {
 		if (!list_empty(page_deferred_list(head))) {
 			ds_queue->split_queue_len--;
-			list_del(page_deferred_list(head));
+			list_del_init(page_deferred_list(head));
 		}
 		spin_unlock(&ds_queue->split_queue_lock);
 		if (mapping) {
@@ -2727,7 +2766,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 				__dec_lruvec_page_state(head, NR_FILE_THPS);
 		}
 
-		__split_huge_page(page, list, end, flags);
+		__split_huge_page(page, list, end, flags, remap);
 		ret = 0;
 	} else {
 		if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) {
@@ -2742,7 +2781,8 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 fail:		if (mapping)
 			xa_unlock(&mapping->i_pages);
 		spin_unlock_irqrestore(&pgdata->lru_lock, flags);
-		remap_page(head, thp_nr_pages(head));
+		if (remap)
+			remap_page(head, thp_nr_pages(head));
 		ret = -EBUSY;
 	}
 
@@ -2758,6 +2798,36 @@ fail:		if (mapping)
 	return ret;
 }
 
+int split_huge_page_to_list(struct page *page, struct list_head *list)
+{
+	return __split_huge_page_to_list(page, list, true);
+}
+
+/*
+ * Split a migrating huge page.
+ * The caller should have mmap_lock_read() held, the huge page unmapped and
+ * isolated, and the PMD page table entry set to a migration entry for the
+ * given head page.
+ */
+int split_migrating_huge_page(struct vm_area_struct *vma, pmd_t *pmd,
+			      unsigned long address, struct page *head)
+{
+	spinlock_t *ptl;
+
+	VM_BUG_ON_PAGE(is_huge_zero_page(head), head);
+	VM_BUG_ON_PAGE(!PageLocked(head), head);
+	VM_BUG_ON_PAGE(!PageHead(head), head);
+	VM_BUG_ON_PAGE(PageWriteback(head), head);
+	VM_BUG_ON_PAGE(PageLRU(head), head);
+	VM_BUG_ON_PAGE(compound_mapcount(head), head);
+
+	ptl = pmd_lock(vma->vm_mm, pmd);
+	__split_huge_pmd_locked(vma, pmd, address, false);
+	spin_unlock(ptl);
+
+	return __split_huge_page_to_list(head, NULL, false);
+}
+
 void free_transhuge_page(struct page *page)
 {
 	struct deferred_split *ds_queue = get_deferred_split_queue(page);
@@ -2766,9 +2836,11 @@ void free_transhuge_page(struct page *page)
 	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
 	if (!list_empty(page_deferred_list(page))) {
 		ds_queue->split_queue_len--;
-		list_del(page_deferred_list(page));
+		list_del_init(page_deferred_list(page));
 	}
 	spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
+	if (is_device_private_page(page))
+		return;
 	free_compound_page(page);
 }
 
@@ -2986,6 +3058,10 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
 		pmde = pmd_mksoft_dirty(pmde);
 	if (is_write_migration_entry(entry))
 		pmde = maybe_pmd_mkwrite(pmde, vma);
+	if (unlikely(is_device_private_page(new))) {
+		entry = make_device_private_entry(new, pmd_write(pmde));
+		pmde = swp_entry_to_pmd(entry);
+	}
 
 	flush_cache_range(vma, mmun_start, mmun_start + HPAGE_PMD_SIZE);
 	if (PageAnon(new))
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3a12df292712..12d3d79c4e32 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5792,12 +5792,22 @@ static enum mc_target_type get_mctgt_type_thp(struct vm_area_struct *vma,
 	struct page *page = NULL;
 	enum mc_target_type ret = MC_TARGET_NONE;
 
-	if (unlikely(is_swap_pmd(pmd))) {
-		VM_BUG_ON(thp_migration_supported() &&
-				  !is_pmd_migration_entry(pmd));
+	if (!(mc.flags & MOVE_ANON))
 		return ret;
+	if (unlikely(is_swap_pmd(pmd))) {
+		swp_entry_t entry = pmd_to_swp_entry(pmd);
+
+		if (!is_device_private_entry(entry)) {
+			VM_BUG_ON(thp_migration_supported() &&
+					  !is_pmd_migration_entry(pmd));
+			return ret;
+		}
+		page = device_private_entry_to_page(entry);
+		ret = MC_TARGET_DEVICE;
+	} else {
+		page = pmd_page(pmd);
+		ret = MC_TARGET_PAGE;
 	}
-	page = pmd_page(pmd);
 	VM_BUG_ON_PAGE(!page || !PageHead(page), page);
 	if (!(mc.flags & MOVE_ANON))
 		return ret;
@@ -5828,12 +5838,7 @@ static int mem_cgroup_count_precharge_pte_range(pmd_t *pmd,
 
 	ptl = pmd_trans_huge_lock(pmd, vma);
 	if (ptl) {
-		/*
-		 * Note their can not be MC_TARGET_DEVICE for now as we do not
-		 * support transparent huge page with MEMORY_DEVICE_PRIVATE but
-		 * this might change.
-		 */
-		if (get_mctgt_type_thp(vma, addr, *pmd, NULL) == MC_TARGET_PAGE)
+		if (get_mctgt_type_thp(vma, addr, *pmd, NULL))
 			mc.precharge += HPAGE_PMD_NR;
 		spin_unlock(ptl);
 		return 0;
diff --git a/mm/memory.c b/mm/memory.c
index f8d66f0e8da7..963c168a93dc 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4485,9 +4485,15 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
 
 		barrier();
 		if (unlikely(is_swap_pmd(orig_pmd))) {
+			swp_entry_t entry = pmd_to_swp_entry(orig_pmd);
+
+			if (is_device_private_entry(entry)) {
+				vmf.page = device_private_entry_to_page(entry);
+				return vmf.page->pgmap->ops->migrate_to_ram(&vmf);
+			}
 			VM_BUG_ON(thp_migration_supported() &&
-					  !is_pmd_migration_entry(orig_pmd));
-			if (is_pmd_migration_entry(orig_pmd))
+					  !is_migration_entry(entry));
+			if (is_migration_entry(entry))
 				pmd_migration_entry_wait(mm, vmf.pmd);
 			return 0;
 		}
diff --git a/mm/memremap.c b/mm/memremap.c
index d72ce30da94e..8b4e6f12e58f 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -92,7 +92,7 @@ static unsigned long pfn_next(unsigned long pfn)
 {
 	if (pfn % 1024 == 0)
 		cond_resched();
-	return pfn + 1;
+	return pfn + thp_nr_pages(pfn_to_page(pfn));
 }
 
 /*
@@ -509,6 +509,8 @@ void free_devmap_managed_page(struct page *page)
 	__ClearPageWaiters(page);
 
 	mem_cgroup_uncharge(page);
+	if (PageHead(page))
+		free_transhuge_page(page);
 
 	/*
 	 * When a device_private page is freed, the page->mapping field
diff --git a/mm/migrate.c b/mm/migrate.c
index 665516319b66..7b69a5f91d0a 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -51,6 +51,7 @@
 #include <linux/oom.h>
 
 #include <asm/tlbflush.h>
+#include <asm/pgalloc.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/migrate.h>
@@ -2275,19 +2276,28 @@ static int migrate_vma_collect_hole(unsigned long start,
 {
 	struct migrate_vma *migrate = walk->private;
 	unsigned long addr;
+	unsigned long mpfn;
 
 	/* Only allow populating anonymous memory. */
-	if (!vma_is_anonymous(walk->vma)) {
-		for (addr = start; addr < end; addr += PAGE_SIZE) {
-			migrate->src[migrate->npages] = 0;
-			migrate->dst[migrate->npages] = 0;
-			migrate->npages++;
-		}
-		return 0;
+	if (!vma_is_anonymous(walk->vma) ||
+	    !((migrate->flags & MIGRATE_VMA_SELECT_SYSTEM)))
+		return migrate_vma_collect_skip(start, end, walk);
+
+	if (thp_migration_supported() &&
+	    (migrate->flags & MIGRATE_VMA_SELECT_COMPOUND) &&
+	    (start & ~PMD_MASK) == 0 && (end & ~PMD_MASK) == 0) {
+		migrate->src[migrate->npages] = MIGRATE_PFN_MIGRATE |
+						MIGRATE_PFN_COMPOUND;
+		migrate->dst[migrate->npages] = 0;
+		migrate->npages++;
+		migrate->cpages++;
+		return migrate_vma_collect_skip(start + PAGE_SIZE, end, walk);
 	}
 
+	mpfn = (migrate->vma->vm_flags & VM_WRITE) ?
+		(MIGRATE_PFN_MIGRATE | MIGRATE_PFN_WRITE) : MIGRATE_PFN_MIGRATE;
 	for (addr = start; addr < end; addr += PAGE_SIZE) {
-		migrate->src[migrate->npages] = MIGRATE_PFN_MIGRATE;
+		migrate->src[migrate->npages] = mpfn;
 		migrate->dst[migrate->npages] = 0;
 		migrate->npages++;
 		migrate->cpages++;
@@ -2296,59 +2306,133 @@ static int migrate_vma_collect_hole(unsigned long start,
 	return 0;
 }
 
-static int migrate_vma_collect_pmd(pmd_t *pmdp,
-				   unsigned long start,
-				   unsigned long end,
-				   struct mm_walk *walk)
+static int migrate_vma_handle_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;
+	struct page *page;
+	unsigned long write = 0;
+	int ret;
 
-again:
-	if (pmd_none(*pmdp))
+	ptl = pmd_lock(mm, pmdp);
+	if (pmd_none(*pmdp)) {
+		spin_unlock(ptl);
 		return migrate_vma_collect_hole(start, end, -1, walk);
-
+	}
 	if (pmd_trans_huge(*pmdp)) {
-		struct page *page;
-
-		ptl = pmd_lock(mm, pmdp);
-		if (unlikely(!pmd_trans_huge(*pmdp))) {
+		if (!(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM)) {
 			spin_unlock(ptl);
-			goto again;
+			return migrate_vma_collect_skip(start, end, walk);
 		}
-
 		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;
+			return migrate_vma_collect_hole(start, end, -1, walk);
+		}
+		if (pmd_write(*pmdp))
+			write = MIGRATE_PFN_WRITE;
+	} else if (!pmd_present(*pmdp)) {
+		swp_entry_t entry = pmd_to_swp_entry(*pmdp);
+
+		if (is_migration_entry(entry)) {
+			bool wait;
 
-			get_page(page);
+			page = migration_entry_to_page(entry);
+			wait = get_page_unless_zero(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, -1,
-								walk);
+			if (wait)
+				put_and_wait_on_page_locked(page);
+			return -EAGAIN;
+		}
+		if (!is_device_private_entry(entry)) {
+			spin_unlock(ptl);
+			return migrate_vma_collect_skip(start, end, walk);
+		}
+		page = device_private_entry_to_page(entry);
+		if (!(migrate->flags & MIGRATE_VMA_SELECT_DEVICE_PRIVATE) ||
+		    page->pgmap->owner != migrate->pgmap_owner) {
+			spin_unlock(ptl);
+			return migrate_vma_collect_skip(start, end, walk);
 		}
+		if (is_write_device_private_entry(entry))
+			write = MIGRATE_PFN_WRITE;
+	} else {
+		spin_unlock(ptl);
+		return -EAGAIN;
+	}
+
+	get_page(page);
+	if (unlikely(!trylock_page(page))) {
+		spin_unlock(ptl);
+		put_page(page);
+		return migrate_vma_collect_skip(start, end, walk);
+	}
+	if (thp_migration_supported() &&
+	    (migrate->flags & MIGRATE_VMA_SELECT_COMPOUND) &&
+	    (start & ~PMD_MASK) == 0 && (start + PMD_SIZE) == end) {
+		struct page_vma_mapped_walk vmw = {
+			.vma = vma,
+			.address = start,
+			.pmd = pmdp,
+			.ptl = ptl,
+		};
+
+		migrate->src[migrate->npages] = write |
+			migrate_pfn(page_to_pfn(page)) |
+			MIGRATE_PFN_MIGRATE | MIGRATE_PFN_LOCKED |
+			MIGRATE_PFN_COMPOUND;
+		migrate->dst[migrate->npages] = 0;
+		migrate->npages++;
+		migrate->cpages++;
+		migrate_vma_collect_skip(start + PAGE_SIZE, end, walk);
+
+		/* Note this also removes the page from the rmap. */
+		set_pmd_migration_entry(&vmw, page);
+		spin_unlock(ptl);
+
+		return 0;
+	}
+	spin_unlock(ptl);
+
+	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, -1, walk);
+
+	/* This just causes migrate_vma_collect_pmd() to handle PTEs. */
+	return -ENOENT;
+}
+
+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_trans_huge(*pmdp) || !pmd_present(*pmdp)) {
+		int ret = migrate_vma_handle_pmd(pmdp, start, end, walk);
+
+		if (!ret)
+			return 0;
+		if (ret == -EAGAIN)
+			goto again;
 	}
 
-	if (unlikely(pmd_bad(*pmdp)))
+	if (unlikely(pmd_bad(*pmdp) || pmd_devmap(*pmdp)))
 		return migrate_vma_collect_skip(start, end, walk);
 
 	ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
@@ -2404,8 +2488,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
 			mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
 		}
 
-		/* FIXME support THP */
-		if (!page || !page->mapping || PageTransCompound(page)) {
+		if (!page || !page->mapping) {
 			mpfn = 0;
 			goto next;
 		}
@@ -2527,14 +2610,6 @@ static bool migrate_vma_check_page(struct page *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)) {
 		/*
@@ -2833,13 +2908,191 @@ int migrate_vma_setup(struct migrate_vma *args)
 }
 EXPORT_SYMBOL(migrate_vma_setup);
 
+static pmd_t *find_pmd(struct mm_struct *mm, unsigned long addr)
+{
+	pgd_t *pgdp;
+	p4d_t *p4dp;
+	pud_t *pudp;
+
+	pgdp = pgd_offset(mm, addr);
+	p4dp = p4d_alloc(mm, pgdp, addr);
+	if (!p4dp)
+		return NULL;
+	pudp = pud_alloc(mm, p4dp, addr);
+	if (!pudp)
+		return NULL;
+	return pmd_alloc(mm, pudp, addr);
+}
+
+#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
+/*
+ * This code closely follows:
+ * do_huge_pmd_anonymous_page()
+ *   __do_huge_pmd_anonymous_page()
+ * except that the page being inserted is likely to be a device private page
+ * instead of an allocated or zero page.
+ */
+static int insert_huge_pmd_anonymous_page(struct vm_area_struct *vma,
+					  unsigned long haddr,
+					  struct page *page,
+					  unsigned long *src,
+					  pmd_t *pmdp)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	unsigned int i;
+	spinlock_t *ptl;
+	bool flush = false;
+	pgtable_t pgtable;
+	gfp_t gfp;
+	pmd_t entry;
+
+	if (WARN_ON_ONCE(compound_order(page) != HPAGE_PMD_ORDER))
+		goto abort;
+
+	if (unlikely(anon_vma_prepare(vma)))
+		goto abort;
+
+	prep_transhuge_page(page);
+
+	gfp = GFP_TRANSHUGE_LIGHT;
+	if (mem_cgroup_charge(page, mm, gfp))
+		goto abort;
+
+	pgtable = pte_alloc_one(mm);
+	if (unlikely(!pgtable))
+		goto abort;
+
+	__SetPageUptodate(page);
+
+	if (is_zone_device_page(page)) {
+		if (!is_device_private_page(page))
+			goto pgtable_abort;
+		entry = swp_entry_to_pmd(make_device_private_entry(page,
+						vma->vm_flags & VM_WRITE));
+	} else {
+		entry = mk_huge_pmd(page, vma->vm_page_prot);
+		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
+	}
+
+	ptl = pmd_lock(mm, pmdp);
+
+	if (check_stable_address_space(mm))
+		goto unlock_abort;
+
+	/*
+	 * Check for userfaultfd but do not deliver the fault. Instead,
+	 * just back off.
+	 */
+	if (userfaultfd_missing(vma))
+		goto unlock_abort;
+
+	if (pmd_present(*pmdp)) {
+		if (!is_huge_zero_pmd(*pmdp))
+			goto unlock_abort;
+		flush = true;
+	} else if (!pmd_none(*pmdp))
+		goto unlock_abort;
+
+	get_page(page);
+	page_add_new_anon_rmap(page, vma, haddr, true);
+	if (!is_zone_device_page(page))
+		lru_cache_add_inactive_or_unevictable(page, vma);
+	if (flush) {
+		pte_free(mm, pgtable);
+		flush_cache_range(vma, haddr, haddr + HPAGE_PMD_SIZE);
+		pmdp_invalidate(vma, haddr, pmdp);
+	} else {
+		pgtable_trans_huge_deposit(mm, pmdp, pgtable);
+		mm_inc_nr_ptes(mm);
+	}
+	set_pmd_at(mm, haddr, pmdp, entry);
+	update_mmu_cache_pmd(vma, haddr, pmdp);
+	add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
+	spin_unlock(ptl);
+	count_vm_event(THP_FAULT_ALLOC);
+	count_memcg_event_mm(mm, THP_FAULT_ALLOC);
+
+	return 0;
+
+unlock_abort:
+	spin_unlock(ptl);
+pgtable_abort:
+	pte_free(mm, pgtable);
+abort:
+	for (i = 0; i < HPAGE_PMD_NR; i++)
+		src[i] &= ~MIGRATE_PFN_MIGRATE;
+	return -EINVAL;
+}
+
+static void migrate_vma_split(struct migrate_vma *migrate, unsigned long i,
+			      unsigned long addr)
+{
+	const unsigned long npages = i + HPAGE_PMD_NR;
+	unsigned long mpfn;
+	unsigned long j;
+	bool migrating = false;
+	struct page *page;
+
+	migrate->src[i] &= ~MIGRATE_PFN_COMPOUND;
+
+	/* If no part of the THP is migrating, we can skip splitting. */
+	for (j = i; j < npages; j++) {
+		if (migrate->dst[j] & MIGRATE_PFN_VALID) {
+			migrating = true;
+			break;
+		}
+	}
+	if (!migrating)
+		return;
+
+	mpfn = migrate->src[i];
+	page = migrate_pfn_to_page(mpfn);
+	if (page) {
+		pmd_t *pmdp;
+		int ret;
+
+		pmdp = find_pmd(migrate->vma->vm_mm, addr);
+		if (!pmdp) {
+			migrate->src[i] = mpfn & ~MIGRATE_PFN_MIGRATE;
+			return;
+		}
+		ret = split_migrating_huge_page(migrate->vma, pmdp, addr, page);
+		if (ret) {
+			migrate->src[i] = mpfn & ~MIGRATE_PFN_MIGRATE;
+			return;
+		}
+		while (++i < npages) {
+			mpfn += 1UL << MIGRATE_PFN_SHIFT;
+			migrate->src[i] = mpfn;
+		}
+	} else {
+		while (++i < npages)
+			migrate->src[i] = mpfn;
+	}
+}
+#else
+static int insert_huge_pmd_anonymous_page(struct vm_area_struct *vma,
+					  unsigned long haddr,
+					  struct page *page,
+					  unsigned long *src,
+					  pmd_t *pmdp)
+{
+	return 0;
+}
+
+static void migrate_vma_split(struct migrate_vma *migrate, unsigned long i,
+			      unsigned long addr)
+{
+}
+#endif
+
 /*
  * This code closely matches the code in:
  *   __handle_mm_fault()
  *     handle_pte_fault()
  *       do_anonymous_page()
- * to map in an anonymous zero page but the struct page will be a ZONE_DEVICE
- * private page.
+ * to map in an anonymous zero page except the struct page is already allocated
+ * and will likely be a ZONE_DEVICE private page.
  */
 static void migrate_vma_insert_page(struct migrate_vma *migrate,
 				    unsigned long addr,
@@ -2852,9 +3105,6 @@ static void migrate_vma_insert_page(struct migrate_vma *migrate,
 	bool flush = false;
 	spinlock_t *ptl;
 	pte_t entry;
-	pgd_t *pgdp;
-	p4d_t *p4dp;
-	pud_t *pudp;
 	pmd_t *pmdp;
 	pte_t *ptep;
 
@@ -2862,19 +3112,25 @@ static void migrate_vma_insert_page(struct migrate_vma *migrate,
 	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);
+	pmdp = find_pmd(mm, addr);
 	if (!pmdp)
 		goto abort;
 
-	if (pmd_trans_huge(*pmdp) || pmd_devmap(*pmdp))
-		goto abort;
+	if (thp_migration_supported() && *dst & MIGRATE_PFN_COMPOUND) {
+		int ret = insert_huge_pmd_anonymous_page(vma, addr, page, src,
+							 pmdp);
+		if (ret)
+			goto abort;
+		return;
+	}
+	if (!pmd_none(*pmdp)) {
+		if (pmd_trans_huge(*pmdp)) {
+			if (!is_huge_zero_pmd(*pmdp))
+				goto abort;
+			__split_huge_pmd(vma, pmdp, addr, false, NULL);
+		} else if (pmd_leaf(*pmdp))
+			goto abort;
+	}
 
 	/*
 	 * Use pte_alloc() instead of pte_alloc_map().  We can't run
@@ -2909,9 +3165,11 @@ static void migrate_vma_insert_page(struct migrate_vma *migrate,
 		if (is_device_private_page(page)) {
 			swp_entry_t swp_entry;
 
-			swp_entry = make_device_private_entry(page, vma->vm_flags & VM_WRITE);
+			swp_entry = make_device_private_entry(page,
+						vma->vm_flags & VM_WRITE);
 			entry = swp_entry_to_pte(swp_entry);
-		}
+		} else
+			goto abort;
 	} else {
 		entry = mk_pte(page, vma->vm_page_prot);
 		if (vma->vm_flags & VM_WRITE)
@@ -2940,10 +3198,10 @@ static void migrate_vma_insert_page(struct migrate_vma *migrate,
 		goto unlock_abort;
 
 	inc_mm_counter(mm, MM_ANONPAGES);
+	get_page(page);
 	page_add_new_anon_rmap(page, vma, addr, false);
 	if (!is_zone_device_page(page))
 		lru_cache_add_inactive_or_unevictable(page, vma);
-	get_page(page);
 
 	if (flush) {
 		flush_cache_page(vma, addr, pte_pfn(*ptep));
@@ -2957,7 +3215,6 @@ static void migrate_vma_insert_page(struct migrate_vma *migrate,
 	}
 
 	pte_unmap_unlock(ptep, ptl);
-	*src = MIGRATE_PFN_MIGRATE;
 	return;
 
 unlock_abort:
@@ -2988,11 +3245,23 @@ void migrate_vma_pages(struct migrate_vma *migrate)
 		struct address_space *mapping;
 		int r;
 
+		/*
+		 * If the caller didn't allocate a THP, split the PMD and
+		 * fix up the src array.
+		 */
+		if (thp_migration_supported() &&
+		    (migrate->src[i] & MIGRATE_PFN_MIGRATE) &&
+		    (migrate->src[i] & MIGRATE_PFN_COMPOUND) &&
+		    !(migrate->dst[i] & MIGRATE_PFN_COMPOUND))
+			migrate_vma_split(migrate, i, addr);
+
+		newpage = migrate_pfn_to_page(migrate->dst[i]);
 		if (!newpage) {
 			migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
 			continue;
 		}
 
+		page = migrate_pfn_to_page(migrate->src[i]);
 		if (!page) {
 			if (!(migrate->src[i] & MIGRATE_PFN_MIGRATE))
 				continue;
diff --git a/mm/rmap.c b/mm/rmap.c
index 1b84945d655c..13eb0247d8b7 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1497,7 +1497,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 		}
 
 		if (IS_ENABLED(CONFIG_MIGRATION) &&
-		    (flags & TTU_MIGRATION) &&
+		    (flags & (TTU_MIGRATION | TTU_SPLIT_FREEZE)) &&
 		    is_zone_device_page(page)) {
 			swp_entry_t entry;
 			pte_t swp_pte;
-- 
2.20.1