1 files changed, 185 insertions, 203 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index f3ee6d8d5e2e..425401b2d4e1 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -35,7 +35,6 @@
 #include <linux/compat.h>
 #include <linux/hugetlb.h>
 #include <linux/gfp.h>
-#include <linux/pfn_t.h>
 #include <linux/page_idle.h>
 #include <linux/page_owner.h>
 #include <linux/sched/mm.h>
@@ -44,15 +43,57 @@
 #include <linux/sched/sysctl.h>
 #include <linux/memory-tiers.h>
 #include <linux/pagewalk.h>
+#include <linux/balloon_compaction.h>
+#include <linux/zsmalloc.h>
 
 #include <asm/tlbflush.h>
 
 #include <trace/events/migrate.h>
 
 #include "internal.h"
+#include "swap.h"
 
-bool isolate_movable_page(struct page *page, isolate_mode_t mode)
+static const struct movable_operations *page_movable_ops(struct page *page)
 {
+	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
+
+	/*
+	 * If we enable page migration for a page of a certain type by marking
+	 * it as movable, the page type must be sticky until the page gets freed
+	 * back to the buddy.
+	 */
+#ifdef CONFIG_BALLOON_COMPACTION
+	if (PageOffline(page))
+		/* Only balloon compaction sets PageOffline pages movable. */
+		return &balloon_mops;
+#endif /* CONFIG_BALLOON_COMPACTION */
+#if defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION)
+	if (PageZsmalloc(page))
+		return &zsmalloc_mops;
+#endif /* defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION) */
+	return NULL;
+}
+
+/**
+ * isolate_movable_ops_page - isolate a movable_ops page for migration
+ * @page: The page.
+ * @mode: The isolation mode.
+ *
+ * Try to isolate a movable_ops page for migration. Will fail if the page is
+ * not a movable_ops page, if the page is already isolated for migration
+ * or if the page was just was released by its owner.
+ *
+ * Once isolated, the page cannot get freed until it is either putback
+ * or migrated.
+ *
+ * Returns true if isolation succeeded, otherwise false.
+ */
+bool isolate_movable_ops_page(struct page *page, isolate_mode_t mode)
+{
+	/*
+	 * TODO: these pages will not be folios in the future. All
+	 * folio dependencies will have to be removed.
+	 */
 	struct folio *folio = folio_get_nontail_page(page);
 	const struct movable_operations *mops;
 
@@ -69,11 +110,14 @@ bool isolate_movable_page(struct page *page, isolate_mode_t mode)
 		goto out;
 
 	/*
-	 * Check movable flag before taking the page lock because
+	 * Check for movable_ops pages before taking the page lock because
 	 * we use non-atomic bitops on newly allocated page flags so
 	 * unconditionally grabbing the lock ruins page's owner side.
+	 *
+	 * Note that once a page has movable_ops, it will stay that way
+	 * until the page was freed.
 	 */
-	if (unlikely(!__folio_test_movable(folio)))
+	if (unlikely(!page_has_movable_ops(page)))
 		goto out_putfolio;
 
 	/*
@@ -90,18 +134,20 @@ bool isolate_movable_page(struct page *page, isolate_mode_t mode)
 	if (unlikely(!folio_trylock(folio)))
 		goto out_putfolio;
 
-	if (!folio_test_movable(folio) || folio_test_isolated(folio))
+	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
+	if (PageMovableOpsIsolated(page))
 		goto out_no_isolated;
 
-	mops = folio_movable_ops(folio);
-	VM_BUG_ON_FOLIO(!mops, folio);
+	mops = page_movable_ops(page);
+	if (WARN_ON_ONCE(!mops))
+		goto out_no_isolated;
 
-	if (!mops->isolate_page(&folio->page, mode))
+	if (!mops->isolate_page(page, mode))
 		goto out_no_isolated;
 
 	/* Driver shouldn't use the isolated flag */
-	WARN_ON_ONCE(folio_test_isolated(folio));
-	folio_set_isolated(folio);
+	VM_WARN_ON_ONCE_PAGE(PageMovableOpsIsolated(page), page);
+	SetPageMovableOpsIsolated(page);
 	folio_unlock(folio);
 
 	return true;
@@ -114,12 +160,69 @@ out:
 	return false;
 }
 
-static void putback_movable_folio(struct folio *folio)
+/**
+ * putback_movable_ops_page - putback an isolated movable_ops page
+ * @page: The isolated page.
+ *
+ * Putback an isolated movable_ops page.
+ *
+ * After the page was putback, it might get freed instantly.
+ */
+static void putback_movable_ops_page(struct page *page)
 {
-	const struct movable_operations *mops = folio_movable_ops(folio);
+	/*
+	 * TODO: these pages will not be folios in the future. All
+	 * folio dependencies will have to be removed.
+	 */
+	struct folio *folio = page_folio(page);
 
-	mops->putback_page(&folio->page);
-	folio_clear_isolated(folio);
+	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
+	VM_WARN_ON_ONCE_PAGE(!PageMovableOpsIsolated(page), page);
+	folio_lock(folio);
+	page_movable_ops(page)->putback_page(page);
+	ClearPageMovableOpsIsolated(page);
+	folio_unlock(folio);
+	folio_put(folio);
+}
+
+/**
+ * migrate_movable_ops_page - migrate an isolated movable_ops page
+ * @dst: The destination page.
+ * @src: The source page.
+ * @mode: The migration mode.
+ *
+ * Migrate an isolated movable_ops page.
+ *
+ * If the src page was already released by its owner, the src page is
+ * un-isolated (putback) and migration succeeds; the migration core will be the
+ * owner of both pages.
+ *
+ * If the src page was not released by its owner and the migration was
+ * successful, the owner of the src page and the dst page are swapped and
+ * the src page is un-isolated.
+ *
+ * If migration fails, the ownership stays unmodified and the src page
+ * remains isolated: migration may be retried later or the page can be putback.
+ *
+ * TODO: migration core will treat both pages as folios and lock them before
+ * this call to unlock them after this call. Further, the folio refcounts on
+ * src and dst are also released by migration core. These pages will not be
+ * folios in the future, so that must be reworked.
+ *
+ * Returns MIGRATEPAGE_SUCCESS on success, otherwise a negative error
+ * code.
+ */
+static int migrate_movable_ops_page(struct page *dst, struct page *src,
+		enum migrate_mode mode)
+{
+	int rc = MIGRATEPAGE_SUCCESS;
+
+	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(src), src);
+	VM_WARN_ON_ONCE_PAGE(!PageMovableOpsIsolated(src), src);
+	rc = page_movable_ops(src)->migrate_page(dst, src, mode);
+	if (rc == MIGRATEPAGE_SUCCESS)
+		ClearPageMovableOpsIsolated(src);
+	return rc;
 }
 
 /*
@@ -141,20 +244,8 @@ void putback_movable_pages(struct list_head *l)
 			continue;
 		}
 		list_del(&folio->lru);
-		/*
-		 * We isolated non-lru movable folio so here we can use
-		 * __folio_test_movable because LRU folio's mapping cannot
-		 * have PAGE_MAPPING_MOVABLE.
-		 */
-		if (unlikely(__folio_test_movable(folio))) {
-			VM_BUG_ON_FOLIO(!folio_test_isolated(folio), folio);
-			folio_lock(folio);
-			if (folio_test_movable(folio))
-				putback_movable_folio(folio);
-			else
-				folio_clear_isolated(folio);
-			folio_unlock(folio);
-			folio_put(folio);
+		if (unlikely(page_has_movable_ops(&folio->page))) {
+			putback_movable_ops_page(&folio->page);
 		} else {
 			node_stat_mod_folio(folio, NR_ISOLATED_ANON +
 					folio_is_file_lru(folio), -folio_nr_pages(folio));
@@ -166,26 +257,20 @@ void putback_movable_pages(struct list_head *l)
 /* Must be called with an elevated refcount on the non-hugetlb folio */
 bool isolate_folio_to_list(struct folio *folio, struct list_head *list)
 {
-	bool isolated, lru;
-
 	if (folio_test_hugetlb(folio))
 		return folio_isolate_hugetlb(folio, list);
 
-	lru = !__folio_test_movable(folio);
-	if (lru)
-		isolated = folio_isolate_lru(folio);
-	else
-		isolated = isolate_movable_page(&folio->page,
-						ISOLATE_UNEVICTABLE);
-
-	if (!isolated)
-		return false;
-
-	list_add(&folio->lru, list);
-	if (lru)
+	if (page_has_movable_ops(&folio->page)) {
+		if (!isolate_movable_ops_page(&folio->page,
+					      ISOLATE_UNEVICTABLE))
+			return false;
+	} else {
+		if (!folio_isolate_lru(folio))
+			return false;
 		node_stat_add_folio(folio, NR_ISOLATED_ANON +
 				    folio_is_file_lru(folio));
-
+	}
+	list_add(&folio->lru, list);
 	return true;
 }
 
@@ -445,20 +530,6 @@ unlock:
 }
 #endif
 
-static int folio_expected_refs(struct address_space *mapping,
-		struct folio *folio)
-{
-	int refs = 1;
-	if (!mapping)
-		return refs;
-
-	refs += folio_nr_pages(folio);
-	if (folio_test_private(folio))
-		refs++;
-
-	return refs;
-}
-
 /*
  * Replace the folio in the mapping.
  *
@@ -601,7 +672,7 @@ static int __folio_migrate_mapping(struct address_space *mapping,
 int folio_migrate_mapping(struct address_space *mapping,
 		struct folio *newfolio, struct folio *folio, int extra_count)
 {
-	int expected_count = folio_expected_refs(mapping, folio) + extra_count;
+	int expected_count = folio_expected_ref_count(folio) + extra_count + 1;
 
 	if (folio_ref_count(folio) != expected_count)
 		return -EAGAIN;
@@ -618,7 +689,7 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
 				   struct folio *dst, struct folio *src)
 {
 	XA_STATE(xas, &mapping->i_pages, folio_index(src));
-	int rc, expected_count = folio_expected_refs(mapping, src);
+	int rc, expected_count = folio_expected_ref_count(src) + 1;
 
 	if (folio_ref_count(src) != expected_count)
 		return -EAGAIN;
@@ -749,7 +820,7 @@ static int __migrate_folio(struct address_space *mapping, struct folio *dst,
 			   struct folio *src, void *src_private,
 			   enum migrate_mode mode)
 {
-	int rc, expected_count = folio_expected_refs(mapping, src);
+	int rc, expected_count = folio_expected_ref_count(src) + 1;
 
 	/* Check whether src does not have extra refs before we do more work */
 	if (folio_ref_count(src) != expected_count)
@@ -837,7 +908,7 @@ static int __buffer_migrate_folio(struct address_space *mapping,
 		return migrate_folio(mapping, dst, src, mode);
 
 	/* Check whether page does not have extra refs before we do more work */
-	expected_count = folio_expected_refs(mapping, src);
+	expected_count = folio_expected_ref_count(src) + 1;
 	if (folio_ref_count(src) != expected_count)
 		return -EAGAIN;
 
@@ -845,9 +916,11 @@ static int __buffer_migrate_folio(struct address_space *mapping,
 		return -EAGAIN;
 
 	if (check_refs) {
-		bool busy;
+		bool busy, migrating;
 		bool invalidated = false;
 
+		migrating = test_and_set_bit_lock(BH_Migrate, &head->b_state);
+		VM_WARN_ON_ONCE(migrating);
 recheck_buffers:
 		busy = false;
 		spin_lock(&mapping->i_private_lock);
@@ -859,12 +932,12 @@ recheck_buffers:
 			}
 			bh = bh->b_this_page;
 		} while (bh != head);
+		spin_unlock(&mapping->i_private_lock);
 		if (busy) {
 			if (invalidated) {
 				rc = -EAGAIN;
 				goto unlock_buffers;
 			}
-			spin_unlock(&mapping->i_private_lock);
 			invalidate_bh_lrus();
 			invalidated = true;
 			goto recheck_buffers;
@@ -883,7 +956,7 @@ recheck_buffers:
 
 unlock_buffers:
 	if (check_refs)
-		spin_unlock(&mapping->i_private_lock);
+		clear_bit_unlock(BH_Migrate, &head->b_state);
 	bh = head;
 	do {
 		unlock_buffer(bh);
@@ -945,66 +1018,20 @@ int filemap_migrate_folio(struct address_space *mapping,
 EXPORT_SYMBOL_GPL(filemap_migrate_folio);
 
 /*
- * Writeback a folio to clean the dirty state
- */
-static int writeout(struct address_space *mapping, struct folio *folio)
-{
-	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 (!folio_clear_dirty_for_io(folio))
-		/* Someone else already triggered a write */
-		return -EAGAIN;
-
-	/*
-	 * A dirty folio may imply that the underlying filesystem has
-	 * the folio on some queue. So the folio must be clean for
-	 * migration. Writeout may mean we lose the lock and the
-	 * folio state is no longer what we checked for earlier.
-	 * At this point we know that the migration attempt cannot
-	 * be successful.
-	 */
-	remove_migration_ptes(folio, folio, 0);
-
-	rc = mapping->a_ops->writepage(&folio->page, &wbc);
-
-	if (rc != AOP_WRITEPAGE_ACTIVATE)
-		/* unlocked. Relock */
-		folio_lock(folio);
-
-	return (rc < 0) ? -EIO : -EAGAIN;
-}
-
-/*
  * Default handling if a filesystem does not provide a migration function.
  */
 static int fallback_migrate_folio(struct address_space *mapping,
 		struct folio *dst, struct folio *src, enum migrate_mode mode)
 {
-	if (folio_test_dirty(src)) {
-		/* Only writeback folios in full synchronous migration */
-		switch (mode) {
-		case MIGRATE_SYNC:
-			break;
-		default:
-			return -EBUSY;
-		}
-		return writeout(mapping, src);
-	}
+	WARN_ONCE(mapping->a_ops->writepages,
+			"%ps does not implement migrate_folio\n",
+			mapping->a_ops);
+	if (folio_test_dirty(src))
+		return -EBUSY;
 
 	/*
-	 * Buffers may be managed in a filesystem specific way.
-	 * We must have no buffers or drop them.
+	 * Filesystem may have private data at folio->private that we
+	 * can't migrate automatically.
 	 */
 	if (!filemap_release_folio(src, GFP_KERNEL))
 		return mode == MIGRATE_SYNC ? -EAGAIN : -EBUSY;
@@ -1013,11 +1040,12 @@ static int fallback_migrate_folio(struct address_space *mapping,
 }
 
 /*
- * Move a page to a newly allocated page
- * The page is locked and all ptes have been successfully removed.
+ * Move a src folio to a newly allocated dst folio.
+ *
+ * The src and dst folios are locked and the src folios was unmapped from
+ * the page tables.
  *
- * The new page will have replaced the old page if this function
- * is successful.
+ * On success, the src folio was replaced by the dst folio.
  *
  * Return value:
  *   < 0 - error code
@@ -1026,78 +1054,40 @@ static int fallback_migrate_folio(struct address_space *mapping,
 static int move_to_new_folio(struct folio *dst, struct folio *src,
 				enum migrate_mode mode)
 {
+	struct address_space *mapping = folio_mapping(src);
 	int rc = -EAGAIN;
-	bool is_lru = !__folio_test_movable(src);
 
 	VM_BUG_ON_FOLIO(!folio_test_locked(src), src);
 	VM_BUG_ON_FOLIO(!folio_test_locked(dst), dst);
 
-	if (likely(is_lru)) {
-		struct address_space *mapping = folio_mapping(src);
-
-		if (!mapping)
-			rc = migrate_folio(mapping, dst, src, mode);
-		else if (mapping_inaccessible(mapping))
-			rc = -EOPNOTSUPP;
-		else if (mapping->a_ops->migrate_folio)
-			/*
-			 * Most folios have a mapping and most filesystems
-			 * provide a migrate_folio callback. Anonymous folios
-			 * are part of swap space which also has its own
-			 * migrate_folio callback. This is the most common path
-			 * for page migration.
-			 */
-			rc = mapping->a_ops->migrate_folio(mapping, dst, src,
-								mode);
-		else
-			rc = fallback_migrate_folio(mapping, dst, src, mode);
-	} else {
-		const struct movable_operations *mops;
-
+	if (!mapping)
+		rc = migrate_folio(mapping, dst, src, mode);
+	else if (mapping_inaccessible(mapping))
+		rc = -EOPNOTSUPP;
+	else if (mapping->a_ops->migrate_folio)
 		/*
-		 * In case of non-lru page, it could be released after
-		 * isolation step. In that case, we shouldn't try migration.
+		 * Most folios have a mapping and most filesystems
+		 * provide a migrate_folio callback. Anonymous folios
+		 * are part of swap space which also has its own
+		 * migrate_folio callback. This is the most common path
+		 * for page migration.
 		 */
-		VM_BUG_ON_FOLIO(!folio_test_isolated(src), src);
-		if (!folio_test_movable(src)) {
-			rc = MIGRATEPAGE_SUCCESS;
-			folio_clear_isolated(src);
-			goto out;
-		}
-
-		mops = folio_movable_ops(src);
-		rc = mops->migrate_page(&dst->page, &src->page, mode);
-		WARN_ON_ONCE(rc == MIGRATEPAGE_SUCCESS &&
-				!folio_test_isolated(src));
-	}
+		rc = mapping->a_ops->migrate_folio(mapping, dst, src,
+							mode);
+	else
+		rc = fallback_migrate_folio(mapping, dst, src, mode);
 
-	/*
-	 * When successful, old pagecache src->mapping must be cleared before
-	 * src is freed; but stats require that PageAnon be left as PageAnon.
-	 */
 	if (rc == MIGRATEPAGE_SUCCESS) {
-		if (__folio_test_movable(src)) {
-			VM_BUG_ON_FOLIO(!folio_test_isolated(src), src);
-
-			/*
-			 * We clear PG_movable under page_lock so any compactor
-			 * cannot try to migrate this page.
-			 */
-			folio_clear_isolated(src);
-		}
-
 		/*
-		 * Anonymous and movable src->mapping will be cleared by
-		 * free_pages_prepare so don't reset it here for keeping
-		 * the type to work PageAnon, for example.
+		 * For pagecache folios, src->mapping must be cleared before src
+		 * is freed. Anonymous folios must stay anonymous until freed.
 		 */
-		if (!folio_mapping_flags(src))
+		if (!folio_test_anon(src))
 			src->mapping = NULL;
 
 		if (likely(!folio_is_zone_device(dst)))
 			flush_dcache_folio(dst);
 	}
-out:
 	return rc;
 }
 
@@ -1164,12 +1154,7 @@ static void migrate_folio_undo_dst(struct folio *dst, bool locked,
 static void migrate_folio_done(struct folio *src,
 			       enum migrate_reason reason)
 {
-	/*
-	 * Compaction can migrate also non-LRU pages which are
-	 * not accounted to NR_ISOLATED_*. They can be recognized
-	 * as __folio_test_movable
-	 */
-	if (likely(!__folio_test_movable(src)) && reason != MR_DEMOTION)
+	if (likely(!page_has_movable_ops(&src->page)) && reason != MR_DEMOTION)
 		mod_node_page_state(folio_pgdat(src), NR_ISOLATED_ANON +
 				    folio_is_file_lru(src), -folio_nr_pages(src));
 
@@ -1188,7 +1173,6 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,
 	int rc = -EAGAIN;
 	int old_page_state = 0;
 	struct anon_vma *anon_vma = NULL;
-	bool is_lru = data_race(!__folio_test_movable(src));
 	bool locked = false;
 	bool dst_locked = false;
 
@@ -1289,7 +1273,7 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,
 		goto out;
 	dst_locked = true;
 
-	if (unlikely(!is_lru)) {
+	if (unlikely(page_has_movable_ops(&src->page))) {
 		__migrate_folio_record(dst, old_page_state, anon_vma);
 		return MIGRATEPAGE_UNMAP;
 	}
@@ -1348,20 +1332,23 @@ static int migrate_folio_move(free_folio_t put_new_folio, unsigned long private,
 	int rc;
 	int old_page_state = 0;
 	struct anon_vma *anon_vma = NULL;
-	bool is_lru = !__folio_test_movable(src);
 	struct list_head *prev;
 
 	__migrate_folio_extract(dst, &old_page_state, &anon_vma);
 	prev = dst->lru.prev;
 	list_del(&dst->lru);
 
+	if (unlikely(page_has_movable_ops(&src->page))) {
+		rc = migrate_movable_ops_page(&dst->page, &src->page, mode);
+		if (rc)
+			goto out;
+		goto out_unlock_both;
+	}
+
 	rc = move_to_new_folio(dst, src, mode);
 	if (rc)
 		goto out;
 
-	if (unlikely(!is_lru))
-		goto out_unlock_both;
-
 	/*
 	 * When successful, push dst to LRU immediately: so that if it
 	 * turns out to be an mlocked page, remove_migration_ptes() will
@@ -1380,7 +1367,7 @@ static int migrate_folio_move(free_folio_t put_new_folio, unsigned long private,
 
 out_unlock_both:
 	folio_unlock(dst);
-	set_page_owner_migrate_reason(&dst->page, reason);
+	folio_set_owner_migrate_reason(dst, reason);
 	/*
 	 * If migration is successful, decrease refcount of dst,
 	 * which will not free the page because new page owner increased
@@ -2376,13 +2363,6 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
 		}
 
 		/*
-		 * The move_pages() man page does not have an -EEXIST choice, so
-		 * use -EFAULT instead.
-		 */
-		if (err == -EEXIST)
-			err = -EFAULT;
-
-		/*
 		 * If the page is already on the target node (!err), store the
 		 * node, otherwise, store the err.
 		 */
@@ -2456,6 +2436,7 @@ set_status:
 
 static int get_compat_pages_array(const void __user *chunk_pages[],
 				  const void __user * __user *pages,
+				  unsigned long chunk_offset,
 				  unsigned long chunk_nr)
 {
 	compat_uptr_t __user *pages32 = (compat_uptr_t __user *)pages;
@@ -2463,7 +2444,7 @@ static int get_compat_pages_array(const void __user *chunk_pages[],
 	int i;
 
 	for (i = 0; i < chunk_nr; i++) {
-		if (get_user(p, pages32 + i))
+		if (get_user(p, pages32 + chunk_offset + i))
 			return -EFAULT;
 		chunk_pages[i] = compat_ptr(p);
 	}
@@ -2482,27 +2463,28 @@ static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
 #define DO_PAGES_STAT_CHUNK_NR 16UL
 	const void __user *chunk_pages[DO_PAGES_STAT_CHUNK_NR];
 	int chunk_status[DO_PAGES_STAT_CHUNK_NR];
+	unsigned long chunk_offset = 0;
 
 	while (nr_pages) {
 		unsigned long chunk_nr = min(nr_pages, DO_PAGES_STAT_CHUNK_NR);
 
 		if (in_compat_syscall()) {
 			if (get_compat_pages_array(chunk_pages, pages,
-						   chunk_nr))
+						   chunk_offset, chunk_nr))
 				break;
 		} else {
-			if (copy_from_user(chunk_pages, pages,
+			if (copy_from_user(chunk_pages, pages + chunk_offset,
 				      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)))
+		if (copy_to_user(status + chunk_offset, chunk_status,
+				 chunk_nr * sizeof(*status)))
 			break;
 
-		pages += chunk_nr;
-		status += chunk_nr;
+		chunk_offset += chunk_nr;
 		nr_pages -= chunk_nr;
 	}
 	return nr_pages ? -EFAULT : 0;