[PATCH v9 0/6] Btrfs: implement swap file support

[PATCH v9 0/6] Btrfs: implement swap file support

[Omar Sandoval]

From: Omar Sandoval <osandov@fb.com>

Hi,

This series implements swap file support for Btrfs.

Changes from v8 [1]:

- Fixed a bug in btrfs_swap_activate() which would cause us to miss some
  file extents if they were merged into one extent map entry.
- Fixed build for !CONFIG_SWAP.
- Changed all error messages to KERN_WARN.
- Unindented long error messages.

I've Cc'd Jon and Al on patch 3 this time, so hopefully we can get an
ack for that one, too.

Thanks!

1: https://www.spinics.net/lists/linux-btrfs/msg82267.html

Omar Sandoval (6):
  mm: split SWP_FILE into SWP_ACTIVATED and SWP_FS
  mm: export add_swap_extent()
  vfs: update swap_{,de}activate documentation
  Btrfs: prevent ioctls from interfering with a swap file
  Btrfs: rename get_chunk_map() and make it non-static
  Btrfs: support swap files

 Documentation/filesystems/Locking |  17 +-
 Documentation/filesystems/vfs.txt |  12 +-
 fs/btrfs/ctree.h                  |  29 +++
 fs/btrfs/dev-replace.c            |   8 +
 fs/btrfs/disk-io.c                |   4 +
 fs/btrfs/inode.c                  | 338 ++++++++++++++++++++++++++++++
 fs/btrfs/ioctl.c                  |  31 ++-
 fs/btrfs/relocation.c             |  18 +-
 fs/btrfs/volumes.c                |  82 ++++++--
 fs/btrfs/volumes.h                |   2 +
 include/linux/swap.h              |  13 +-
 mm/page_io.c                      |   6 +-
 mm/swapfile.c                     |  14 +-
 13 files changed, 523 insertions(+), 51 deletions(-)

-- 
2.19.0

[PATCH v9 1/6] mm: split SWP_FILE into SWP_ACTIVATED and SWP_FS

[Omar Sandoval]

From: Omar Sandoval <osandov@fb.com>

The SWP_FILE flag serves two purposes: to make swap_{read,write}page()
go through the filesystem, and to make swapoff() call
->swap_deactivate(). For Btrfs, we want the latter but not the former,
so split this flag into two. This makes us always call
->swap_deactivate() if ->swap_activate() succeeded, not just if it
didn't add any swap extents itself.

This also resolves the issue of the very misleading name of SWP_FILE,
which is only used for swap files over NFS.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 include/linux/swap.h | 13 +++++++------
 mm/page_io.c         |  6 +++---
 mm/swapfile.c        | 13 ++++++++-----
 3 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 8e2c11e692ba..0fda0aa743f0 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -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
diff --git a/mm/page_io.c b/mm/page_io.c
index aafd19ec1db4..e8653c368069 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -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);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index d954b71c4f9c..d3f95833d12e 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -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;
 		}
-- 
2.19.0

[PATCH v9 2/6] mm: export add_swap_extent()

[Omar Sandoval]

From: Omar Sandoval <osandov@fb.com>

Btrfs currently does not support swap files because swap's use of bmap
does not work with copy-on-write and multiple devices. See commit
35054394c4b3 ("Btrfs: stop providing a bmap operation to avoid swapfile
corruptions"). However, the swap code has a mechanism for the filesystem
to manually add swap extents using add_swap_extent() from the
->swap_activate() aop. iomap has done this since commit 67482129cdab
("iomap: add a swapfile activation function"). Btrfs will do the same in
a later patch, so export add_swap_extent().

Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 mm/swapfile.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index d3f95833d12e..51cb30de17bc 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -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
-- 
2.19.0

[PATCH v9 3/6] vfs: update swap_{,de}activate documentation

[Omar Sandoval]

From: Omar Sandoval <osandov@fb.com>

The documentation for these functions is wrong in several ways:

- swap_activate() is called with the inode locked
- swap_activate() takes a swap_info_struct * and a sector_t *
- swap_activate() can also return a positive number of extents it added
  itself
- swap_deactivate() does not return anything

Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Omar Sandoval <osandov@fb.com>
---
Hi, Jon, Al, could I get an ack on this patch? Thanks!

 Documentation/filesystems/Locking | 17 +++++++----------
 Documentation/filesystems/vfs.txt | 12 ++++++++----
 2 files changed, 15 insertions(+), 14 deletions(-)

diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index efea228ccd8a..b970c8c2ee22 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -210,8 +210,9 @@ prototypes:
 	int (*launder_page)(struct page *);
 	int (*is_partially_uptodate)(struct page *, unsigned long, unsigned long);
 	int (*error_remove_page)(struct address_space *, struct page *);
-	int (*swap_activate)(struct file *);
-	int (*swap_deactivate)(struct file *);
+	int (*swap_activate)(struct swap_info_struct *, struct file *,
+			     sector_t *);
+	void (*swap_deactivate)(struct file *);
 
 locking rules:
 	All except set_page_dirty and freepage may block
@@ -235,8 +236,8 @@ putback_page:		yes
 launder_page:		yes
 is_partially_uptodate:	yes
 error_remove_page:	yes
-swap_activate:		no
-swap_deactivate:	no
+swap_activate:					yes
+swap_deactivate:				no
 
 	->write_begin(), ->write_end() and ->readpage() may be called from
 the request handler (/dev/loop).
@@ -333,14 +334,10 @@ cleaned, or an error value if not. Note that in order to prevent the page
 getting mapped back in and redirtied, it needs to be kept locked
 across the entire operation.
 
-	->swap_activate will be called with a non-zero argument on
-files backing (non block device backed) swapfiles. A return value
-of zero indicates success, in which case this file can be used for
-backing swapspace. The swapspace operations will be proxied to the
-address space operations.
+	->swap_activate is called from sys_swapon() with the inode locked.
 
 	->swap_deactivate() will be called in the sys_swapoff()
-path after ->swap_activate() returned success.
+path after ->swap_activate() returned success. The inode is not locked.
 
 ----------------------- file_lock_operations ------------------------------
 prototypes:
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index a6c6a8af48a2..6e14db053eaa 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -652,8 +652,9 @@ struct address_space_operations {
 					unsigned long);
 	void (*is_dirty_writeback) (struct page *, bool *, bool *);
 	int (*error_remove_page) (struct mapping *mapping, struct page *page);
-	int (*swap_activate)(struct file *);
-	int (*swap_deactivate)(struct file *);
+	int (*swap_activate)(struct swap_info_struct *, struct file *,
+			     sector_t *);
+	void (*swap_deactivate)(struct file *);
 };
 
   writepage: called by the VM to write a dirty page to backing store.
@@ -830,8 +831,11 @@ struct address_space_operations {
 
   swap_activate: Called when swapon is used on a file to allocate
 	space if necessary and pin the block lookup information in
-	memory. A return value of zero indicates success,
-	in which case this file can be used to back swapspace.
+	memory. If this returns zero, the swap system will call the address
+	space operations ->readpage() and ->direct_IO(). Alternatively, this
+	may call add_swap_extent() and return the number of extents added, in
+	which case the swap system will use the provided blocks directly
+	instead of going through the filesystem.
 
   swap_deactivate: Called during swapoff on files where swap_activate
 	was successful.
-- 
2.19.0

[PATCH v9 4/6] Btrfs: prevent ioctls from interfering with a swap file

[Omar Sandoval]

From: Omar Sandoval <osandov@fb.com>

A later patch will implement swap file support for Btrfs, but before we
do that, we need to make sure that the various Btrfs ioctls cannot
change a swap file.

When a swap file is active, we must make sure that the extents of the
file are not moved and that they don't become shared. That means that
the following are not safe:

- chattr +c (enable compression)
- reflink
- dedupe
- snapshot
- defrag

Don't allow those to happen on an active swap file.

Additionally, balance, resize, device remove, and device replace are
also unsafe if they affect an active swapfile. Add a red-black tree of
block groups and devices which contain an active swapfile. Relocation
checks each block group against this tree and skips it or errors out for
balance or resize, respectively. Device remove and device replace check
the tree for the device they will operate on.

Note that we don't have to worry about chattr -C (disable nocow), which
we ignore for non-empty files, because an active swapfile must be
non-empty and can't be truncated. We also don't have to worry about
autodefrag because it's only done on COW files. Truncate and fallocate
are already taken care of by the generic code. Device add doesn't do
relocation so it's not an issue, either.

Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 fs/btrfs/ctree.h       | 29 +++++++++++++++++++++++
 fs/btrfs/dev-replace.c |  8 +++++++
 fs/btrfs/disk-io.c     |  4 ++++
 fs/btrfs/ioctl.c       | 31 +++++++++++++++++++++---
 fs/btrfs/relocation.c  | 18 ++++++++++----
 fs/btrfs/volumes.c     | 53 ++++++++++++++++++++++++++++++++++++++----
 6 files changed, 131 insertions(+), 12 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 2cddfe7806a4..08df61b8fc87 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -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 {
diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index dec01970d8c5..781006b6fca3 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -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)
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 05dc3c17cb62..2428a73067d2 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -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;
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index d60b6caf09e8..72f56c1bbc74 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -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)
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 8783a1776540..7468a0f55cd2 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -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) {
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index f4405e430da6..aa37ae30bf62 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1882,6 +1882,14 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
 	if (ret)
 		goto out;
 
+	if (btrfs_pinned_by_swapfile(fs_info, device)) {
+		btrfs_warn_in_rcu(fs_info,
+		  "cannot remove device %s (devid %llu) due to active swapfile",
+				  rcu_str_deref(device->name), device->devid);
+		ret = -ETXTBSY;
+		goto out;
+	}
+
 	if (test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state)) {
 		ret = BTRFS_ERROR_DEV_TGT_REPLACE;
 		goto out;
@@ -3626,10 +3634,15 @@ static int __btrfs_balance(struct btrfs_fs_info *fs_info)
 
 		ret = btrfs_relocate_chunk(fs_info, found_key.offset);
 		mutex_unlock(&fs_info->delete_unused_bgs_mutex);
-		if (ret && ret != -ENOSPC)
-			goto error;
 		if (ret == -ENOSPC) {
 			enospc_errors++;
+		} else if (ret == -ETXTBSY) {
+			btrfs_info(fs_info,
+	   "skipping relocation of block group %llu due to active swapfile",
+				   found_key.offset);
+			ret = 0;
+		} else if (ret) {
+			goto error;
 		} else {
 			spin_lock(&fs_info->balance_lock);
 			bctl->stat.completed++;
@@ -4426,10 +4439,16 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
 
 		ret = btrfs_relocate_chunk(fs_info, chunk_offset);
 		mutex_unlock(&fs_info->delete_unused_bgs_mutex);
-		if (ret && ret != -ENOSPC)
-			goto done;
-		if (ret == -ENOSPC)
+		if (ret == -ENOSPC) {
 			failed++;
+		} else if (ret) {
+			if (ret == -ETXTBSY) {
+				btrfs_warn(fs_info,
+		   "could not shrink block group %llu due to active swapfile",
+					   chunk_offset);
+			}
+			goto done;
+		}
 	} while (key.offset-- > 0);
 
 	if (failed && !retried) {
@@ -7530,3 +7549,27 @@ int btrfs_verify_dev_extents(struct btrfs_fs_info *fs_info)
 	btrfs_free_path(path);
 	return ret;
 }
+
+/*
+ * Check whether the given block group or device is pinned by any inode being
+ * used as a swapfile.
+ */
+bool btrfs_pinned_by_swapfile(struct btrfs_fs_info *fs_info, void *ptr)
+{
+	struct btrfs_swapfile_pin *sp;
+	struct rb_node *node;
+
+	spin_lock(&fs_info->swapfile_pins_lock);
+	node = fs_info->swapfile_pins.rb_node;
+	while (node) {
+		sp = rb_entry(node, struct btrfs_swapfile_pin, node);
+		if (ptr < sp->ptr)
+			node = node->rb_left;
+		else if (ptr > sp->ptr)
+			node = node->rb_right;
+		else
+			break;
+	}
+	spin_unlock(&fs_info->swapfile_pins_lock);
+	return node != NULL;
+}
-- 
2.19.0

[PATCH v9 5/6] Btrfs: rename get_chunk_map() and make it non-static

[Omar Sandoval]

From: Omar Sandoval <osandov@fb.com>

The Btrfs swap code is going to need it, so give it a btrfs_ prefix and
make it non-static.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 fs/btrfs/volumes.c | 29 ++++++++++++++++++-----------
 fs/btrfs/volumes.h |  2 ++
 2 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index aa37ae30bf62..20c26afdd330 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -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;
 
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 23e9285d88de..f4c190c2ab84 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -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)
-- 
2.19.0

[PATCH v9 6/6] Btrfs: support swap files

[Omar Sandoval]

From: Omar Sandoval <osandov@fb.com>

Btrfs has not allowed swap files since commit 35054394c4b3 ("Btrfs: stop
providing a bmap operation to avoid swapfile corruptions"). However, now
that the proper restrictions are in place, Btrfs can support swap files
through the swap file a_ops, similar to iomap in commit 67482129cdab
("iomap: add a swapfile activation function").

For Btrfs, activation needs to make sure that the file can be used as a
swap file, which currently means that it must be fully allocated as
nocow with no compression on one device. It must also do the proper
tracking so that ioctls will not interfere with the swap file.
Deactivation clears this tracking.

Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 fs/btrfs/inode.c | 338 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 338 insertions(+)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 3ea5339603cf..8f8b7079e1ba 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -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 = {
-- 
2.19.0

Re: [PATCH v9 0/6] Btrfs: implement swap file support

[David Sterba]

On Thu, Sep 27, 2018 at 11:17:32AM -0700, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
> This series implements swap file support for Btrfs.
> 
> Changes from v8 [1]:
> 
> - Fixed a bug in btrfs_swap_activate() which would cause us to miss some
>   file extents if they were merged into one extent map entry.
> - Fixed build for !CONFIG_SWAP.
> - Changed all error messages to KERN_WARN.
> - Unindented long error messages.
> 
> I've Cc'd Jon and Al on patch 3 this time, so hopefully we can get an
> ack for that one, too.
> 
> Thanks!
> 
> 1: https://www.spinics.net/lists/linux-btrfs/msg82267.html
> 
> Omar Sandoval (6):
>   mm: split SWP_FILE into SWP_ACTIVATED and SWP_FS
>   mm: export add_swap_extent()
>   vfs: update swap_{,de}activate documentation
>   Btrfs: prevent ioctls from interfering with a swap file
>   Btrfs: rename get_chunk_map() and make it non-static
>   Btrfs: support swap files

Patches 1 and 2 now going through Andrew's tree, the btrfs part will be
delayed and not merged to 4.20. This is a bit unfortuante, I was busy
with the non-feature patches and other things, sorry.

Re: [PATCH v9 0/6] Btrfs: implement swap file support

[Omar Sandoval]

On Fri, Oct 19, 2018 at 05:43:18PM +0200, David Sterba wrote:
> On Thu, Sep 27, 2018 at 11:17:32AM -0700, Omar Sandoval wrote:
> > From: Omar Sandoval <osandov@fb.com>
> > This series implements swap file support for Btrfs.
> > 
> > Changes from v8 [1]:
> > 
> > - Fixed a bug in btrfs_swap_activate() which would cause us to miss some
> >   file extents if they were merged into one extent map entry.
> > - Fixed build for !CONFIG_SWAP.
> > - Changed all error messages to KERN_WARN.
> > - Unindented long error messages.
> > 
> > I've Cc'd Jon and Al on patch 3 this time, so hopefully we can get an
> > ack for that one, too.
> > 
> > Thanks!
> > 
> > 1: https://www.spinics.net/lists/linux-btrfs/msg82267.html
> > 
> > Omar Sandoval (6):
> >   mm: split SWP_FILE into SWP_ACTIVATED and SWP_FS
> >   mm: export add_swap_extent()
> >   vfs: update swap_{,de}activate documentation
> >   Btrfs: prevent ioctls from interfering with a swap file
> >   Btrfs: rename get_chunk_map() and make it non-static
> >   Btrfs: support swap files
> 
> Patches 1 and 2 now going through Andrew's tree, the btrfs part will be
> delayed and not merged to 4.20. This is a bit unfortuante, I was busy
> with the non-feature patches and other things, sorry.

That's perfectly fine with me, thanks, Dave!

Re: [PATCH v9 0/6] Btrfs: implement swap file support

[David Sterba]

On Mon, Oct 22, 2018 at 02:13:27PM -0700, Omar Sandoval wrote:
> > > Omar Sandoval (6):
> > >   mm: split SWP_FILE into SWP_ACTIVATED and SWP_FS
> > >   mm: export add_swap_extent()
> > >   vfs: update swap_{,de}activate documentation

> > >   Btrfs: prevent ioctls from interfering with a swap file
> > >   Btrfs: rename get_chunk_map() and make it non-static
> > >   Btrfs: support swap files
> > 
> > Patches 1 and 2 now going through Andrew's tree, the btrfs part will be
> > delayed and not merged to 4.20. This is a bit unfortuante, I was busy
> > with the non-feature patches and other things, sorry.
> 
> That's perfectly fine with me, than

The 3 btrfs patches are now in misc-next.

Setting up the swap file needs the extra steps to make sure it's a NOCOW
file and preallocated, that's just 2 more commands using common tools.
The surprise may come on an a multi-device filesystem when the chunks
get spread over more devices and the user has no control over that.
Reducing the file size until it fits is a workaround, tough not totally
reliable.

I've explored the error cases (balance, dev delete, adding more
swapfiles). Also a stress test (make -j on kernel). The OOM killer was
able to get the system back after each round after which I added one
more swapfile, until the system was effectively dead.

So the stability seems to be ok, we will need to document the usecase,
constraints and how to properly set up the swapfile, and that's about
it. Thanks.

Re: [PATCH v9 0/6] Btrfs: implement swap file support

[David Sterba]

On Thu, Sep 27, 2018 at 11:17:32AM -0700, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
> This series implements swap file support for Btrfs.
> 
> Changes from v8 [1]:
> 
> - Fixed a bug in btrfs_swap_activate() which would cause us to miss some
>   file extents if they were merged into one extent map entry.
> - Fixed build for !CONFIG_SWAP.
> - Changed all error messages to KERN_WARN.
> - Unindented long error messages.
> 
> I've Cc'd Jon and Al on patch 3 this time, so hopefully we can get an
> ack for that one, too.
> 
> Thanks!
> 
> 1: https://www.spinics.net/lists/linux-btrfs/msg82267.html
> 
> Omar Sandoval (6):
>   mm: split SWP_FILE into SWP_ACTIVATED and SWP_FS
>   mm: export add_swap_extent()
>   vfs: update swap_{,de}activate documentation
>   Btrfs: prevent ioctls from interfering with a swap file
>   Btrfs: rename get_chunk_map() and make it non-static
>   Btrfs: support swap files

fstest generic/472 reports an assertion failure. This is on the updated fstests
git (70c4067285b0bc076), though it should not matter:

[16597.002190] assertion failed: IS_ALIGNED(start, fs_info->sectorsize) && IS_ALIGNED(end + 1, fs_info->sectorsize), file: fs/btrfs/file-item.c, line: 319
[16597.016154] ------------[ cut here ]------------
[16597.020911] kernel BUG at fs/btrfs/ctree.h:3448!
[16597.025692] invalid opcode: 0000 [#1] PREEMPT SMP
[16597.030540] CPU: 1 PID: 2216 Comm: swapon Tainted: G        W         4.19.0-1.ge195904-vanilla+ #343
[16597.030542] Hardware name: empty empty/S3993, BIOS PAQEX0-3 02/24/2008
[16597.030617] RIP: 0010:btrfs_lookup_csums_range+0x3ee/0x6e0 [btrfs]
[16597.030623] RSP: 0018:ffff959a8210fc00 EFLAGS: 00010286
[16597.030626] RAX: 000000000000008b RBX: ffff959a8210fc40 RCX: 0000000000000000
[16597.030628] RDX: 0000000000000000 RSI: ffff89c766fd60a8 RDI: ffff89c766fd60a8
[16597.030630] RBP: 0000000000f10000 R08: 0000000000000001 R09: 0000000000000000
[16597.030631] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[16597.030633] R13: ffff89c74f47c000 R14: 0000000000000000 R15: 0000000000003e4f
[16597.030635] FS:  00007f3d80a18700(0000) GS:ffff89c766e00000(0000) knlGS:0000000000000000
[16597.030637] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[16597.030639] CR2: 00007f3d7fa733b0 CR3: 000000021e0b5000 CR4: 00000000000006e0
[16597.030640] Call Trace:
[16597.030657]  ? __mutex_unlock_slowpath+0x4b/0x2b0
[16597.142625]  ? btrfs_cross_ref_exist+0x6d/0xa0 [btrfs]
[16597.142674]  csum_exist_in_range+0x43/0xc2 [btrfs]
[16597.152938]  can_nocow_extent+0x442/0x4a0 [btrfs]
[16597.152993]  btrfs_swap_activate+0x19f/0x680 [btrfs]
[16597.162947]  __do_sys_swapon+0xdf8/0x1550
[16597.162965]  do_syscall_64+0x5c/0x1b0
[16597.162971]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
[16597.162974] RIP: 0033:0x7f3d7fb1f067
[16597.198875] RSP: 002b:00007ffcf9c49808 EFLAGS: 00000202 ORIG_RAX: 00000000000000a7
[16597.198877] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f3d7fb1f067
[16597.198879] RDX: 00007ffcf9c49910 RSI: 0000000000000000 RDI: 00007ffcf9c4a8f0
[16597.198884] RBP: 0000000000000000 R08: 00007f3d7fdd8c40 R09: 00007f3d8081dfc0
[16597.228520] R10: 000000001cc0c4fd R11: 0000000000000202 R12: 00000000004006a0
[16597.228522] R13: 00007ffcf9c498f0 R14: 0000000000000000 R15: 0000000000000000
[16597.311530] ---[ end trace f4dc8cabefc3e36d ]---
[16597.316318] RIP: 0010:btrfs_lookup_csums_range+0x3ee/0x6e0 [btrfs]
[16597.341828] RSP: 0018:ffff959a8210fc00 EFLAGS: 00010286
[16597.341834] RAX: 000000000000008b RBX: ffff959a8210fc40 RCX: 0000000000000000
[16597.354588] RDX: 0000000000000000 RSI: ffff89c766fd60a8 RDI: ffff89c766fd60a8
[16597.354590] RBP: 0000000000f10000 R08: 0000000000000001 R09: 0000000000000000
[16597.354592] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[16597.354593] R13: ffff89c74f47c000 R14: 0000000000000000 R15: 0000000000003e4f
[16597.354595] FS:  00007f3d80a18700(0000) GS:ffff89c766e00000(0000) knlGS:0000000000000000
[16597.354596] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[16597.354598] CR2: 00007f3d7fa733b0 CR3: 000000021e0b5000 CR4: 00000000000006e0

Re: [PATCH v9 0/6] Btrfs: implement swap file support

[David Sterba]

On Tue, Nov 06, 2018 at 10:54:51AM +0100, David Sterba wrote:
> On Thu, Sep 27, 2018 at 11:17:32AM -0700, Omar Sandoval wrote:
> > From: Omar Sandoval <osandov@fb.com>
> > This series implements swap file support for Btrfs.
> > 
> > Changes from v8 [1]:
> > 
> > - Fixed a bug in btrfs_swap_activate() which would cause us to miss some
> >   file extents if they were merged into one extent map entry.
> > - Fixed build for !CONFIG_SWAP.
> > - Changed all error messages to KERN_WARN.
> > - Unindented long error messages.
> > 
> > I've Cc'd Jon and Al on patch 3 this time, so hopefully we can get an
> > ack for that one, too.
> > 
> > Thanks!
> > 
> > 1: https://www.spinics.net/lists/linux-btrfs/msg82267.html
> > 
> > Omar Sandoval (6):
> >   mm: split SWP_FILE into SWP_ACTIVATED and SWP_FS
> >   mm: export add_swap_extent()
> >   vfs: update swap_{,de}activate documentation
> >   Btrfs: prevent ioctls from interfering with a swap file
> >   Btrfs: rename get_chunk_map() and make it non-static
> >   Btrfs: support swap files
> 
> fstest generic/472 reports an assertion failure. This is on the updated fstests
> git (70c4067285b0bc076), though it should not matter:
> 
> [16597.002190] assertion failed: IS_ALIGNED(start, fs_info->sectorsize) && IS_ALIGNED(end + 1, fs_info->sectorsize), file: fs/btrfs/file-item.c, line: 319

I have to revert the patch for now as it kills the testing machines.

Re: [PATCH v9 0/6] Btrfs: implement swap file support

[Nikolay Borisov]

On 7.11.18 г. 16:49 ч., David Sterba wrote:
> On Tue, Nov 06, 2018 at 10:54:51AM +0100, David Sterba wrote:
>> On Thu, Sep 27, 2018 at 11:17:32AM -0700, Omar Sandoval wrote:
>>> From: Omar Sandoval <osandov@fb.com>
>>> This series implements swap file support for Btrfs.
>>>
>>> Changes from v8 [1]:
>>>
>>> - Fixed a bug in btrfs_swap_activate() which would cause us to miss some
>>>   file extents if they were merged into one extent map entry.
>>> - Fixed build for !CONFIG_SWAP.
>>> - Changed all error messages to KERN_WARN.
>>> - Unindented long error messages.
>>>
>>> I've Cc'd Jon and Al on patch 3 this time, so hopefully we can get an
>>> ack for that one, too.
>>>
>>> Thanks!
>>>
>>> 1: https://www.spinics.net/lists/linux-btrfs/msg82267.html
>>>
>>> Omar Sandoval (6):
>>>   mm: split SWP_FILE into SWP_ACTIVATED and SWP_FS
>>>   mm: export add_swap_extent()
>>>   vfs: update swap_{,de}activate documentation
>>>   Btrfs: prevent ioctls from interfering with a swap file
>>>   Btrfs: rename get_chunk_map() and make it non-static
>>>   Btrfs: support swap files
>>
>> fstest generic/472 reports an assertion failure. This is on the updated fstests
>> git (70c4067285b0bc076), though it should not matter:
>>
>> [16597.002190] assertion failed: IS_ALIGNED(start, fs_info->sectorsize) && IS_ALIGNED(end + 1, fs_info->sectorsize), file: fs/btrfs/file-item.c, line: 319
> 
> I have to revert the patch for now as it kills the testing machines.

The reason is that the isize is not aligned to a sectorsize. Ie it
should be:

+       u64 isize = ALIGN_DOWN(i_size_read(inode), fs_info->sectorsize);

With this fixlet generic/472 succeeds.

> 

Re: [PATCH v9 0/6] Btrfs: implement swap file support

[David Sterba]

On Wed, Nov 07, 2018 at 05:07:00PM +0200, Nikolay Borisov wrote:
> 
> 
> On 7.11.18 г. 16:49 ч., David Sterba wrote:
> > On Tue, Nov 06, 2018 at 10:54:51AM +0100, David Sterba wrote:
> >> On Thu, Sep 27, 2018 at 11:17:32AM -0700, Omar Sandoval wrote:
> >>> From: Omar Sandoval <osandov@fb.com>
> >>> This series implements swap file support for Btrfs.
> >>>
> >>> Changes from v8 [1]:
> >>>
> >>> - Fixed a bug in btrfs_swap_activate() which would cause us to miss some
> >>>   file extents if they were merged into one extent map entry.
> >>> - Fixed build for !CONFIG_SWAP.
> >>> - Changed all error messages to KERN_WARN.
> >>> - Unindented long error messages.
> >>>
> >>> I've Cc'd Jon and Al on patch 3 this time, so hopefully we can get an
> >>> ack for that one, too.
> >>>
> >>> Thanks!
> >>>
> >>> 1: https://www.spinics.net/lists/linux-btrfs/msg82267.html
> >>>
> >>> Omar Sandoval (6):
> >>>   mm: split SWP_FILE into SWP_ACTIVATED and SWP_FS
> >>>   mm: export add_swap_extent()
> >>>   vfs: update swap_{,de}activate documentation
> >>>   Btrfs: prevent ioctls from interfering with a swap file
> >>>   Btrfs: rename get_chunk_map() and make it non-static
> >>>   Btrfs: support swap files
> >>
> >> fstest generic/472 reports an assertion failure. This is on the updated fstests
> >> git (70c4067285b0bc076), though it should not matter:
> >>
> >> [16597.002190] assertion failed: IS_ALIGNED(start, fs_info->sectorsize) && IS_ALIGNED(end + 1, fs_info->sectorsize), file: fs/btrfs/file-item.c, line: 319
> > 
> > I have to revert the patch for now as it kills the testing machines.
> 
> The reason is that the isize is not aligned to a sectorsize. Ie it
> should be:
> 
> +       u64 isize = ALIGN_DOWN(i_size_read(inode), fs_info->sectorsize);
> 
> With this fixlet generic/472 succeeds.

Thanks for the fix, I'll fold it in.

Re: [PATCH v9 0/6] Btrfs: implement swap file support

[Omar Sandoval]

On Wed, Nov 07, 2018 at 04:28:10PM +0100, David Sterba wrote:
> On Wed, Nov 07, 2018 at 05:07:00PM +0200, Nikolay Borisov wrote:
> > 
> > 
> > On 7.11.18 г. 16:49 ч., David Sterba wrote:
> > > On Tue, Nov 06, 2018 at 10:54:51AM +0100, David Sterba wrote:
> > >> On Thu, Sep 27, 2018 at 11:17:32AM -0700, Omar Sandoval wrote:
> > >>> From: Omar Sandoval <osandov@fb.com>
> > >>> This series implements swap file support for Btrfs.
> > >>>
> > >>> Changes from v8 [1]:
> > >>>
> > >>> - Fixed a bug in btrfs_swap_activate() which would cause us to miss some
> > >>>   file extents if they were merged into one extent map entry.
> > >>> - Fixed build for !CONFIG_SWAP.
> > >>> - Changed all error messages to KERN_WARN.
> > >>> - Unindented long error messages.
> > >>>
> > >>> I've Cc'd Jon and Al on patch 3 this time, so hopefully we can get an
> > >>> ack for that one, too.
> > >>>
> > >>> Thanks!
> > >>>
> > >>> 1: https://www.spinics.net/lists/linux-btrfs/msg82267.html
> > >>>
> > >>> Omar Sandoval (6):
> > >>>   mm: split SWP_FILE into SWP_ACTIVATED and SWP_FS
> > >>>   mm: export add_swap_extent()
> > >>>   vfs: update swap_{,de}activate documentation
> > >>>   Btrfs: prevent ioctls from interfering with a swap file
> > >>>   Btrfs: rename get_chunk_map() and make it non-static
> > >>>   Btrfs: support swap files
> > >>
> > >> fstest generic/472 reports an assertion failure. This is on the updated fstests
> > >> git (70c4067285b0bc076), though it should not matter:
> > >>
> > >> [16597.002190] assertion failed: IS_ALIGNED(start, fs_info->sectorsize) && IS_ALIGNED(end + 1, fs_info->sectorsize), file: fs/btrfs/file-item.c, line: 319
> > > 
> > > I have to revert the patch for now as it kills the testing machines.
> > 
> > The reason is that the isize is not aligned to a sectorsize. Ie it
> > should be:
> > 
> > +       u64 isize = ALIGN_DOWN(i_size_read(inode), fs_info->sectorsize);
> > 
> > With this fixlet generic/472 succeeds.
> 
> Thanks for the fix, I'll fold it in.

Thanks, Nikolay, I missed that. I don't think i_size_read() is
necessary, though, since the inode is locked.

Re: [PATCH v9 0/6] Btrfs: implement swap file support

[David Sterba]

On Fri, Nov 09, 2018 at 08:12:39PM -0800, Omar Sandoval wrote:
> On Wed, Nov 07, 2018 at 04:28:10PM +0100, David Sterba wrote:
> > On Wed, Nov 07, 2018 at 05:07:00PM +0200, Nikolay Borisov wrote:
> > > 
> > > 
> > > On 7.11.18 г. 16:49 ч., David Sterba wrote:
> > > > On Tue, Nov 06, 2018 at 10:54:51AM +0100, David Sterba wrote:
> > > >> On Thu, Sep 27, 2018 at 11:17:32AM -0700, Omar Sandoval wrote:
> > > >>> From: Omar Sandoval <osandov@fb.com>
> > > >>> This series implements swap file support for Btrfs.
> > > >>>
> > > >>> Changes from v8 [1]:
> > > >>>
> > > >>> - Fixed a bug in btrfs_swap_activate() which would cause us to miss some
> > > >>>   file extents if they were merged into one extent map entry.
> > > >>> - Fixed build for !CONFIG_SWAP.
> > > >>> - Changed all error messages to KERN_WARN.
> > > >>> - Unindented long error messages.
> > > >>>
> > > >>> I've Cc'd Jon and Al on patch 3 this time, so hopefully we can get an
> > > >>> ack for that one, too.
> > > >>>
> > > >>> Thanks!
> > > >>>
> > > >>> 1: https://www.spinics.net/lists/linux-btrfs/msg82267.html
> > > >>>
> > > >>> Omar Sandoval (6):
> > > >>>   mm: split SWP_FILE into SWP_ACTIVATED and SWP_FS
> > > >>>   mm: export add_swap_extent()
> > > >>>   vfs: update swap_{,de}activate documentation
> > > >>>   Btrfs: prevent ioctls from interfering with a swap file
> > > >>>   Btrfs: rename get_chunk_map() and make it non-static
> > > >>>   Btrfs: support swap files
> > > >>
> > > >> fstest generic/472 reports an assertion failure. This is on the updated fstests
> > > >> git (70c4067285b0bc076), though it should not matter:
> > > >>
> > > >> [16597.002190] assertion failed: IS_ALIGNED(start, fs_info->sectorsize) && IS_ALIGNED(end + 1, fs_info->sectorsize), file: fs/btrfs/file-item.c, line: 319
> > > > 
> > > > I have to revert the patch for now as it kills the testing machines.
> > > 
> > > The reason is that the isize is not aligned to a sectorsize. Ie it
> > > should be:
> > > 
> > > +       u64 isize = ALIGN_DOWN(i_size_read(inode), fs_info->sectorsize);
> > > 
> > > With this fixlet generic/472 succeeds.
> > 
> > Thanks for the fix, I'll fold it in.
> 
> Thanks, Nikolay, I missed that. I don't think i_size_read() is
> necessary, though, since the inode is locked.

Indeed, i_size used and patch pushed to misc-next.