Btrfs: implement swap file support

index 8e2c11e692ba..0fda0aa743f0 100644
@@ -167,13 +167,14 @@ enum {
 	SWP_SOLIDSTATE	= (1 << 4),	/* blkdev seeks are cheap */
 	SWP_CONTINUED	= (1 << 5),	/* swap_map has count continuation */
 	SWP_BLKDEV	= (1 << 6),	/* its a block device */
-	SWP_FILE	= (1 << 7),	/* set after swap_activate success */
-	SWP_AREA_DISCARD = (1 << 8),	/* single-time swap area discards */
-	SWP_PAGE_DISCARD = (1 << 9),	/* freed swap page-cluster discards */
-	SWP_STABLE_WRITES = (1 << 10),	/* no overwrite PG_writeback pages */
-	SWP_SYNCHRONOUS_IO = (1 << 11),	/* synchronous IO is efficient */
+	SWP_ACTIVATED	= (1 << 7),	/* set after swap_activate success */
+	SWP_FS		= (1 << 8),	/* swap file goes through fs */
+	SWP_AREA_DISCARD = (1 << 9),	/* single-time swap area discards */
+	SWP_PAGE_DISCARD = (1 << 10),	/* freed swap page-cluster discards */
+	SWP_STABLE_WRITES = (1 << 11),	/* no overwrite PG_writeback pages */
+	SWP_SYNCHRONOUS_IO = (1 << 12),	/* synchronous IO is efficient */
 					/* add others here before... */
-	SWP_SCANNING	= (1 << 12),	/* refcount in scan_swap_map */
+	SWP_SCANNING	= (1 << 13),	/* refcount in scan_swap_map */
 };
 
 #define SWAP_CLUSTER_MAX 32UL

index aafd19ec1db4..e8653c368069 100644
@@ -283,7 +283,7 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
 	struct swap_info_struct *sis = page_swap_info(page);
 
 	VM_BUG_ON_PAGE(!PageSwapCache(page), page);
-	if (sis->flags & SWP_FILE) {
+	if (sis->flags & SWP_FS) {
 		struct kiocb kiocb;
 		struct file *swap_file = sis->swap_file;
 		struct address_space *mapping = swap_file->f_mapping;

@@ -365,7 +365,7 @@ int swap_readpage(struct page *page, bool synchronous)
 		goto out;
 	}
 
-	if (sis->flags & SWP_FILE) {
+	if (sis->flags & SWP_FS) {
 		struct file *swap_file = sis->swap_file;
 		struct address_space *mapping = swap_file->f_mapping;
 

@@ -423,7 +423,7 @@ int swap_set_page_dirty(struct page *page)
 {
 	struct swap_info_struct *sis = page_swap_info(page);
 
-	if (sis->flags & SWP_FILE) {
+	if (sis->flags & SWP_FS) {
 		struct address_space *mapping = sis->swap_file->f_mapping;
 
 		VM_BUG_ON_PAGE(!PageSwapCache(page), page);

index d954b71c4f9c..d3f95833d12e 100644
@@ -989,7 +989,7 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_size)
 			goto nextsi;
 		}
 		if (size == SWAPFILE_CLUSTER) {
-			if (!(si->flags & SWP_FILE))
+			if (!(si->flags & SWP_FS))
 				n_ret = swap_alloc_cluster(si, swp_entries);
 		} else
 			n_ret = scan_swap_map_slots(si, SWAP_HAS_CACHE,

@@ -2310,12 +2310,13 @@ static void destroy_swap_extents(struct swap_info_struct *sis)
 		kfree(se);
 	}
 
-	if (sis->flags & SWP_FILE) {
+	if (sis->flags & SWP_ACTIVATED) {
 		struct file *swap_file = sis->swap_file;
 		struct address_space *mapping = swap_file->f_mapping;
 
-		sis->flags &= ~SWP_FILE;
-		mapping->a_ops->swap_deactivate(swap_file);
+		sis->flags &= ~SWP_ACTIVATED;
+		if (mapping->a_ops->swap_deactivate)
+			mapping->a_ops->swap_deactivate(swap_file);
 	}
 }
 

@@ -2411,8 +2412,10 @@ static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
 
 	if (mapping->a_ops->swap_activate) {
 		ret = mapping->a_ops->swap_activate(sis, swap_file, span);
+		if (ret >= 0)
+			sis->flags |= SWP_ACTIVATED;
 		if (!ret) {
-			sis->flags |= SWP_FILE;
+			sis->flags |= SWP_FS;
 			ret = add_swap_extent(sis, 0, sis->max, 0);
 			*span = sis->pages;
 		}

index d3f95833d12e..51cb30de17bc 100644
@@ -2365,6 +2365,7 @@ add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
 	list_add_tail(&new_se->list, &sis->first_swap_extent.list);
 	return 1;
 }
+EXPORT_SYMBOL_GPL(add_swap_extent);
 
 /*
  * A `swap extent' is a simple thing which maps a contiguous range of pages

index 2cddfe7806a4..08df61b8fc87 100644
@@ -716,6 +716,28 @@ struct btrfs_fs_devices;
 struct btrfs_balance_control;
 struct btrfs_delayed_root;
 
+/*
+ * Block group or device which contains an active swapfile. Used for preventing
+ * unsafe operations while a swapfile is active.
+ *
+ * These are sorted on (ptr, inode) (note that a block group or device can
+ * contain more than one swapfile). We compare the pointer values because we
+ * don't actually care what the object is, we just need a quick check whether
+ * the object exists in the rbtree.
+ */
+struct btrfs_swapfile_pin {
+	struct rb_node node;
+	void *ptr;
+	struct inode *inode;
+	/*
+	 * If true, ptr points to a struct btrfs_block_group_cache. Otherwise,
+	 * ptr points to a struct btrfs_device.
+	 */
+	bool is_block_group;
+};
+
+bool btrfs_pinned_by_swapfile(struct btrfs_fs_info *fs_info, void *ptr);
+
 #define BTRFS_FS_BARRIER			1
 #define BTRFS_FS_CLOSING_START			2
 #define BTRFS_FS_CLOSING_DONE			3

@@ -1121,6 +1143,10 @@ struct btrfs_fs_info {
 	u32 sectorsize;
 	u32 stripesize;
 
+	/* Block groups and devices containing active swapfiles. */
+	spinlock_t swapfile_pins_lock;
+	struct rb_root swapfile_pins;
+
 #ifdef CONFIG_BTRFS_FS_REF_VERIFY
 	spinlock_t ref_verify_lock;
 	struct rb_root block_tree;

@@ -1286,6 +1312,9 @@ struct btrfs_root {
 	spinlock_t qgroup_meta_rsv_lock;
 	u64 qgroup_meta_rsv_pertrans;
 	u64 qgroup_meta_rsv_prealloc;
+
+	/* Number of active swapfiles */
+	atomic_t nr_swapfiles;
 };
 
 struct btrfs_file_private {

index dec01970d8c5..781006b6fca3 100644
@@ -414,6 +414,14 @@ int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
 	if (ret)
 		return ret;
 
+	if (btrfs_pinned_by_swapfile(fs_info, src_device)) {
+		btrfs_warn_in_rcu(fs_info,
+	  "cannot replace device %s (devid %llu) due to active swapfile",
+				  btrfs_dev_name(src_device),
+				  src_device->devid);
+		return -ETXTBSY;
+	}
+
 	ret = btrfs_init_dev_replace_tgtdev(fs_info, tgtdev_name,
 					    src_device, &tgt_device);
 	if (ret)

index 05dc3c17cb62..2428a73067d2 100644
@@ -1188,6 +1188,7 @@ static void __setup_root(struct btrfs_root *root, struct btrfs_fs_info *fs_info,
 	refcount_set(&root->refs, 1);
 	atomic_set(&root->will_be_snapshotted, 0);
 	atomic_set(&root->snapshot_force_cow, 0);
+	atomic_set(&root->nr_swapfiles, 0);
 	root->log_transid = 0;
 	root->log_transid_committed = -1;
 	root->last_log_commit = 0;

@@ -2782,6 +2783,9 @@ int open_ctree(struct super_block *sb,
 	fs_info->sectorsize = 4096;
 	fs_info->stripesize = 4096;
 
+	spin_lock_init(&fs_info->swapfile_pins_lock);
+	fs_info->swapfile_pins = RB_ROOT;
+
 	ret = btrfs_alloc_stripe_hash_table(fs_info);
 	if (ret) {
 		err = ret;

index d60b6caf09e8..72f56c1bbc74 100644
@@ -290,6 +290,11 @@ static int btrfs_ioctl_setflags(struct file *file, void __user *arg)
 	} else if (fsflags & FS_COMPR_FL) {
 		const char *comp;
 
+		if (IS_SWAPFILE(inode)) {
+			ret = -ETXTBSY;
+			goto out_unlock;
+		}
+
 		binode->flags |= BTRFS_INODE_COMPRESS;
 		binode->flags &= ~BTRFS_INODE_NOCOMPRESS;
 

@@ -752,6 +757,12 @@ static int create_snapshot(struct btrfs_root *root, struct inode *dir,
 	if (!test_bit(BTRFS_ROOT_REF_COWS, &root->state))
 		return -EINVAL;
 
+	if (atomic_read(&root->nr_swapfiles)) {
+		btrfs_warn(fs_info,
+			   "cannot snapshot subvolume with active swapfile");
+		return -ETXTBSY;
+	}
+
 	pending_snapshot = kzalloc(sizeof(*pending_snapshot), GFP_KERNEL);
 	if (!pending_snapshot)
 		return -ENOMEM;

@@ -1503,9 +1514,13 @@ int btrfs_defrag_file(struct inode *inode, struct file *file,
 		}
 
 		inode_lock(inode);
-		if (do_compress)
-			BTRFS_I(inode)->defrag_compress = compress_type;
-		ret = cluster_pages_for_defrag(inode, pages, i, cluster);
+		if (IS_SWAPFILE(inode)) {
+			ret = -ETXTBSY;
+		} else {
+			if (do_compress)
+				BTRFS_I(inode)->defrag_compress = compress_type;
+			ret = cluster_pages_for_defrag(inode, pages, i, cluster);
+		}
 		if (ret < 0) {
 			inode_unlock(inode);
 			goto out_ra;

@@ -3573,6 +3588,11 @@ static int btrfs_extent_same(struct inode *src, u64 loff, u64 olen,
 		goto out_unlock;
 	}
 
+	if (IS_SWAPFILE(src) || IS_SWAPFILE(dst)) {
+		ret = -ETXTBSY;
+		goto out_unlock;
+	}
+
 	tail_len = olen % BTRFS_MAX_DEDUPE_LEN;
 	chunk_count = div_u64(olen, BTRFS_MAX_DEDUPE_LEN);
 	if (chunk_count == 0)

@@ -4269,6 +4289,11 @@ static noinline int btrfs_clone_files(struct file *file, struct file *file_src,
 		goto out_unlock;
 	}
 
+	if (IS_SWAPFILE(src) || IS_SWAPFILE(inode)) {
+		ret = -ETXTBSY;
+		goto out_unlock;
+	}
+
 	/* determine range to clone */
 	ret = -EINVAL;
 	if (off + len > src->i_size || off + len < off)

index 8783a1776540..7468a0f55cd2 100644
@@ -4226,6 +4226,7 @@ static void describe_relocation(struct btrfs_fs_info *fs_info,
  */
 int btrfs_relocate_block_group(struct btrfs_fs_info *fs_info, u64 group_start)
 {
+	struct btrfs_block_group_cache *bg;
 	struct btrfs_root *extent_root = fs_info->extent_root;
 	struct reloc_control *rc;
 	struct inode *inode;

@@ -4234,14 +4235,23 @@ int btrfs_relocate_block_group(struct btrfs_fs_info *fs_info, u64 group_start)
 	int rw = 0;
 	int err = 0;
 
+	bg = btrfs_lookup_block_group(fs_info, group_start);
+	if (!bg)
+		return -ENOENT;
+
+	if (btrfs_pinned_by_swapfile(fs_info, bg)) {
+		btrfs_put_block_group(bg);
+		return -ETXTBSY;
+	}
+
 	rc = alloc_reloc_control();
-	if (!rc)
+	if (!rc) {
+		btrfs_put_block_group(bg);
 		return -ENOMEM;
+	}
 
 	rc->extent_root = extent_root;
-
-	rc->block_group = btrfs_lookup_block_group(fs_info, group_start);
-	BUG_ON(!rc->block_group);
+	rc->block_group = bg;
 
 	ret = btrfs_inc_block_group_ro(rc->block_group);
 	if (ret) {

77 lines not on this page · raw message

index aa37ae30bf62..20c26afdd330 100644
@@ -2714,8 +2714,15 @@ static int btrfs_del_sys_chunk(struct btrfs_fs_info *fs_info, u64 chunk_offset)
 	return ret;
 }
 
-static struct extent_map *get_chunk_map(struct btrfs_fs_info *fs_info,
-					u64 logical, u64 length)
+/*
+ * btrfs_get_chunk_map() - Find the mapping containing the given logical extent.
+ * @logical: Logical block offset in bytes.
+ * @length: Length of extent in bytes.
+ *
+ * Return: Chunk mapping or ERR_PTR.
+ */
+struct extent_map *btrfs_get_chunk_map(struct btrfs_fs_info *fs_info,
+				       u64 logical, u64 length)
 {
 	struct extent_map_tree *em_tree;
 	struct extent_map *em;

@@ -2752,7 +2759,7 @@ int btrfs_remove_chunk(struct btrfs_trans_handle *trans, u64 chunk_offset)
 	int i, ret = 0;
 	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
 
-	em = get_chunk_map(fs_info, chunk_offset, 1);
+	em = btrfs_get_chunk_map(fs_info, chunk_offset, 1);
 	if (IS_ERR(em)) {
 		/*
 		 * This is a logic error, but we don't want to just rely on the

@@ -4902,7 +4909,7 @@ int btrfs_finish_chunk_alloc(struct btrfs_trans_handle *trans,
 	int i = 0;
 	int ret = 0;
 
-	em = get_chunk_map(fs_info, chunk_offset, chunk_size);
+	em = btrfs_get_chunk_map(fs_info, chunk_offset, chunk_size);
 	if (IS_ERR(em))
 		return PTR_ERR(em);
 

@@ -5044,7 +5051,7 @@ int btrfs_chunk_readonly(struct btrfs_fs_info *fs_info, u64 chunk_offset)
 	int miss_ndevs = 0;
 	int i;
 
-	em = get_chunk_map(fs_info, chunk_offset, 1);
+	em = btrfs_get_chunk_map(fs_info, chunk_offset, 1);
 	if (IS_ERR(em))
 		return 1;
 

@@ -5104,7 +5111,7 @@ int btrfs_num_copies(struct btrfs_fs_info *fs_info, u64 logical, u64 len)
 	struct map_lookup *map;
 	int ret;
 
-	em = get_chunk_map(fs_info, logical, len);
+	em = btrfs_get_chunk_map(fs_info, logical, len);
 	if (IS_ERR(em))
 		/*
 		 * We could return errors for these cases, but that could get

@@ -5150,7 +5157,7 @@ unsigned long btrfs_full_stripe_len(struct btrfs_fs_info *fs_info,
 	struct map_lookup *map;
 	unsigned long len = fs_info->sectorsize;
 
-	em = get_chunk_map(fs_info, logical, len);
+	em = btrfs_get_chunk_map(fs_info, logical, len);
 
 	if (!WARN_ON(IS_ERR(em))) {
 		map = em->map_lookup;

@@ -5167,7 +5174,7 @@ int btrfs_is_parity_mirror(struct btrfs_fs_info *fs_info, u64 logical, u64 len)
 	struct map_lookup *map;
 	int ret = 0;
 
-	em = get_chunk_map(fs_info, logical, len);
+	em = btrfs_get_chunk_map(fs_info, logical, len);
 
 	if(!WARN_ON(IS_ERR(em))) {
 		map = em->map_lookup;

@@ -5326,7 +5333,7 @@ static int __btrfs_map_block_for_discard(struct btrfs_fs_info *fs_info,
 	/* discard always return a bbio */
 	ASSERT(bbio_ret);
 
-	em = get_chunk_map(fs_info, logical, length);
+	em = btrfs_get_chunk_map(fs_info, logical, length);
 	if (IS_ERR(em))
 		return PTR_ERR(em);
 

@@ -5652,7 +5659,7 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
 		return __btrfs_map_block_for_discard(fs_info, logical,
 						     *length, bbio_ret);
 
-	em = get_chunk_map(fs_info, logical, *length);
+	em = btrfs_get_chunk_map(fs_info, logical, *length);
 	if (IS_ERR(em))
 		return PTR_ERR(em);
 

@@ -5951,7 +5958,7 @@ int btrfs_rmap_block(struct btrfs_fs_info *fs_info, u64 chunk_start,
 	u64 rmap_len;
 	int i, j, nr = 0;
 
-	em = get_chunk_map(fs_info, chunk_start, 1);
+	em = btrfs_get_chunk_map(fs_info, chunk_start, 1);
 	if (IS_ERR(em))
 		return -EIO;
 

index 23e9285d88de..f4c190c2ab84 100644
@@ -465,6 +465,8 @@ unsigned long btrfs_full_stripe_len(struct btrfs_fs_info *fs_info,
 int btrfs_finish_chunk_alloc(struct btrfs_trans_handle *trans,
 			     u64 chunk_offset, u64 chunk_size);
 int btrfs_remove_chunk(struct btrfs_trans_handle *trans, u64 chunk_offset);
+struct extent_map *btrfs_get_chunk_map(struct btrfs_fs_info *fs_info,
+				       u64 logical, u64 length);
 
 static inline void btrfs_dev_stat_inc(struct btrfs_device *dev,
 				      int index)

index 3ea5339603cf..8f8b7079e1ba 100644
@@ -27,6 +27,7 @@
 #include <linux/uio.h>
 #include <linux/magic.h>
 #include <linux/iversion.h>
+#include <linux/swap.h>
 #include <asm/unaligned.h>
 #include "ctree.h"
 #include "disk-io.h"

@@ -10488,6 +10489,341 @@ void btrfs_set_range_writeback(struct extent_io_tree *tree, u64 start, u64 end)
 	}
 }
 
+#ifdef CONFIG_SWAP
+/*
+ * Add an entry indicating a block group or device which is pinned by a
+ * swapfile. Returns 0 on success, 1 if there is already an entry for it, or a
+ * negative errno on failure.
+ */
+static int btrfs_add_swapfile_pin(struct inode *inode, void *ptr,
+				  bool is_block_group)
+{
+	struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
+	struct btrfs_swapfile_pin *sp, *entry;
+	struct rb_node **p;
+	struct rb_node *parent = NULL;
+
+	sp = kmalloc(sizeof(*sp), GFP_NOFS);
+	if (!sp)
+		return -ENOMEM;
+	sp->ptr = ptr;
+	sp->inode = inode;
+	sp->is_block_group = is_block_group;
+
+	spin_lock(&fs_info->swapfile_pins_lock);
+	p = &fs_info->swapfile_pins.rb_node;
+	while (*p) {
+		parent = *p;
+		entry = rb_entry(parent, struct btrfs_swapfile_pin, node);
+		if (sp->ptr < entry->ptr ||
+		    (sp->ptr == entry->ptr && sp->inode < entry->inode)) {
+			p = &(*p)->rb_left;
+		} else if (sp->ptr > entry->ptr ||
+			   (sp->ptr == entry->ptr && sp->inode > entry->inode)) {
+			p = &(*p)->rb_right;
+		} else {
+			spin_unlock(&fs_info->swapfile_pins_lock);
+			kfree(sp);
+			return 1;
+		}
+	}
+	rb_link_node(&sp->node, parent, p);
+	rb_insert_color(&sp->node, &fs_info->swapfile_pins);
+	spin_unlock(&fs_info->swapfile_pins_lock);
+	return 0;
+}
+
+/* Free all of the entries pinned by this swapfile. */
+static void btrfs_free_swapfile_pins(struct inode *inode)
+{
+	struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
+	struct btrfs_swapfile_pin *sp;
+	struct rb_node *node, *next;
+
+	spin_lock(&fs_info->swapfile_pins_lock);
+	node = rb_first(&fs_info->swapfile_pins);
+	while (node) {
+		next = rb_next(node);
+		sp = rb_entry(node, struct btrfs_swapfile_pin, node);
+		if (sp->inode == inode) {
+			rb_erase(&sp->node, &fs_info->swapfile_pins);
+			if (sp->is_block_group)
+				btrfs_put_block_group(sp->ptr);
+			kfree(sp);
+		}
+		node = next;
+	}
+	spin_unlock(&fs_info->swapfile_pins_lock);
+}
+
+struct btrfs_swap_info {
+	u64 start;
+	u64 block_start;
+	u64 block_len;
+	u64 lowest_ppage;
+	u64 highest_ppage;
+	unsigned long nr_pages;
+	int nr_extents;
+};
+
+static int btrfs_add_swap_extent(struct swap_info_struct *sis,
+				 struct btrfs_swap_info *bsi)
+{
+	unsigned long nr_pages;
+	u64 first_ppage, first_ppage_reported, next_ppage;
+	int ret;
+
+	first_ppage = ALIGN(bsi->block_start, PAGE_SIZE) >> PAGE_SHIFT;
+	next_ppage = ALIGN_DOWN(bsi->block_start + bsi->block_len,
+				PAGE_SIZE) >> PAGE_SHIFT;
+
+	if (first_ppage >= next_ppage)
+		return 0;
+	nr_pages = next_ppage - first_ppage;
+
+	first_ppage_reported = first_ppage;
+	if (bsi->start == 0)
+		first_ppage_reported++;
+	if (bsi->lowest_ppage > first_ppage_reported)
+		bsi->lowest_ppage = first_ppage_reported;
+	if (bsi->highest_ppage < (next_ppage - 1))
+		bsi->highest_ppage = next_ppage - 1;
+
+	ret = add_swap_extent(sis, bsi->nr_pages, nr_pages, first_ppage);
+	if (ret < 0)
+		return ret;
+	bsi->nr_extents += ret;
+	bsi->nr_pages += nr_pages;
+	return 0;
+}
+
+static void btrfs_swap_deactivate(struct file *file)
+{
+	struct inode *inode = file_inode(file);
+
+	btrfs_free_swapfile_pins(inode);
+	atomic_dec(&BTRFS_I(inode)->root->nr_swapfiles);
+}
+
+static int btrfs_swap_activate(struct swap_info_struct *sis, struct file *file,
+			       sector_t *span)
+{
+	struct inode *inode = file_inode(file);
+	struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
+	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
+	struct extent_state *cached_state = NULL;
+	struct extent_map *em = NULL;
+	struct btrfs_device *device = NULL;
+	struct btrfs_swap_info bsi = {
+		.lowest_ppage = (sector_t)-1ULL,
+	};
+	int ret = 0;
+	u64 isize = inode->i_size;
+	u64 start;
+
+	/*
+	 * If the swap file was just created, make sure delalloc is done. If the
+	 * file changes again after this, the user is doing something stupid and
+	 * we don't really care.
+	 */
+	ret = btrfs_wait_ordered_range(inode, 0, (u64)-1);
+	if (ret)
+		return ret;
+
+	/*
+	 * The inode is locked, so these flags won't change after we check them.
+	 */
+	if (BTRFS_I(inode)->flags & BTRFS_INODE_COMPRESS) {
+		btrfs_warn(fs_info, "swapfile must not be compressed");
+		return -EINVAL;
+	}
+	if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW)) {
+		btrfs_warn(fs_info, "swapfile must not be copy-on-write");
+		return -EINVAL;
+	}
+	if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
+		btrfs_warn(fs_info, "swapfile must not be checksummed");
+		return -EINVAL;
+	}
+
+	/*
+	 * Balance or device remove/replace/resize can move stuff around from
+	 * under us. The EXCL_OP flag makes sure they aren't running/won't run
+	 * concurrently while we are mapping the swap extents, and
+	 * fs_info->swapfile_pins prevents them from running while the swap file
+	 * is active and moving the extents. Note that this also prevents a
+	 * concurrent device add which isn't actually necessary, but it's not
+	 * really worth the trouble to allow it.
+	 */
+	if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
+		btrfs_warn(fs_info,
+	   "cannot activate swapfile while exclusive operation is running");
+		return -EBUSY;
+	}
+	/*
+	 * Snapshots can create extents which require COW even if NODATACOW is
+	 * set. We use this counter to prevent snapshots. We must increment it
+	 * before walking the extents because we don't want a concurrent
+	 * snapshot to run after we've already checked the extents.
+	 */
+	atomic_inc(&BTRFS_I(inode)->root->nr_swapfiles);
+
+	lock_extent_bits(io_tree, 0, isize - 1, &cached_state);
+	start = 0;
+	while (start < isize) {
+		u64 logical_block_start, physical_block_start;
+		struct btrfs_block_group_cache *bg;
+		u64 len = isize - start;
+
+		em = btrfs_get_extent(BTRFS_I(inode), NULL, 0, start, len, 0);
+		if (IS_ERR(em)) {
+			ret = PTR_ERR(em);
+			goto out;
+		}
+
+		if (em->block_start == EXTENT_MAP_HOLE) {
+			btrfs_warn(fs_info, "swapfile must not have holes");
+			ret = -EINVAL;
+			goto out;
+		}
+		if (em->block_start == EXTENT_MAP_INLINE) {
+			/*
+			 * It's unlikely we'll ever actually find ourselves
+			 * here, as a file small enough to fit inline won't be
+			 * big enough to store more than the swap header, but in
+			 * case something changes in the future, let's catch it
+			 * here rather than later.
+			 */
+			btrfs_warn(fs_info, "swapfile must not be inline");
+			ret = -EINVAL;
+			goto out;
+		}
+		if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags)) {
+			btrfs_warn(fs_info, "swapfile must not be compressed");
+			ret = -EINVAL;
+			goto out;
+		}
+
+		logical_block_start = em->block_start + (start - em->start);
+		len = min(len, em->len - (start - em->start));
+		free_extent_map(em);
+		em = NULL;
+
+		ret = can_nocow_extent(inode, start, &len, NULL, NULL, NULL);
+		if (ret < 0) {
+			goto out;
+		} else if (ret) {
+			ret = 0;
+		} else {
+			btrfs_warn(fs_info,
+				   "swapfile must not be copy-on-write");
+			ret = -EINVAL;
+			goto out;
+		}
+
+		em = btrfs_get_chunk_map(fs_info, logical_block_start, len);
+		if (IS_ERR(em)) {
+			ret = PTR_ERR(em);
+			goto out;
+		}
+
+		if (em->map_lookup->type & BTRFS_BLOCK_GROUP_PROFILE_MASK) {
+			btrfs_warn(fs_info,
+				   "swapfile must have single data profile");
+			ret = -EINVAL;
+			goto out;
+		}
+
+		if (device == NULL) {
+			device = em->map_lookup->stripes[0].dev;
+			ret = btrfs_add_swapfile_pin(inode, device, false);
+			if (ret == 1)
+				ret = 0;
+			else if (ret)
+				goto out;
+		} else if (device != em->map_lookup->stripes[0].dev) {
+			btrfs_warn(fs_info, "swapfile must be on one device");
+			ret = -EINVAL;
+			goto out;
+		}
+
+		physical_block_start = (em->map_lookup->stripes[0].physical +
+					(logical_block_start - em->start));
+		len = min(len, em->len - (logical_block_start - em->start));
+		free_extent_map(em);
+		em = NULL;
+
+		bg = btrfs_lookup_block_group(fs_info, logical_block_start);
+		if (!bg) {
+			btrfs_warn(fs_info,
+			   "could not find block group containing swapfile");
+			ret = -EINVAL;
+			goto out;
+		}
+
+		ret = btrfs_add_swapfile_pin(inode, bg, true);
+		if (ret) {
+			btrfs_put_block_group(bg);
+			if (ret == 1)
+				ret = 0;
+			else
+				goto out;
+		}
+
+		if (bsi.block_len &&
+		    bsi.block_start + bsi.block_len == physical_block_start) {
+			bsi.block_len += len;
+		} else {
+			if (bsi.block_len) {
+				ret = btrfs_add_swap_extent(sis, &bsi);
+				if (ret)
+					goto out;
+			}
+			bsi.start = start;
+			bsi.block_start = physical_block_start;
+			bsi.block_len = len;
+		}
+
+		start += len;
+	}
+
+	if (bsi.block_len)
+		ret = btrfs_add_swap_extent(sis, &bsi);
+
+out:
+	if (!IS_ERR_OR_NULL(em))
+		free_extent_map(em);
+
+	unlock_extent_cached(io_tree, 0, isize - 1, &cached_state);
+
+	if (ret)
+		btrfs_swap_deactivate(file);
+
+	clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
+
+	if (ret)
+		return ret;
+
+	if (device)
+		sis->bdev = device->bdev;
+	*span = bsi.highest_ppage - bsi.lowest_ppage + 1;
+	sis->max = bsi.nr_pages;
+	sis->pages = bsi.nr_pages - 1;
+	sis->highest_bit = bsi.nr_pages - 1;
+	return bsi.nr_extents;
+}
+#else
+static void btrfs_swap_deactivate(struct file *file)
+{
+}
+
+static int btrfs_swap_activate(struct swap_info_struct *sis, struct file *file,
+			       sector_t *span)
+{
+	return -EOPNOTSUPP;
+}
+#endif
+
 static const struct inode_operations btrfs_dir_inode_operations = {
 	.getattr	= btrfs_getattr,
 	.lookup		= btrfs_lookup,

@@ -10565,6 +10901,8 @@ static const struct address_space_operations btrfs_aops = {
 	.releasepage	= btrfs_releasepage,
 	.set_page_dirty	= btrfs_set_page_dirty,
 	.error_remove_page = generic_error_remove_page,
+	.swap_activate	= btrfs_swap_activate,
+	.swap_deactivate = btrfs_swap_deactivate,
 };
 
 static const struct address_space_operations btrfs_symlink_aops = {