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Ethan Lien f5d5b54349 btrfs: use tagged writepage to mitigate livelock of snapshot 
[ Upstream commit 3cd24c6980 ]

Snapshot is expected to be fast. But if there are writers steadily
creating dirty pages in our subvolume, the snapshot may take a very long
time to complete. To fix the problem, we use tagged writepage for
snapshot flusher as we do in the generic write_cache_pages(), so we can
omit pages dirtied after the snapshot command.

This does not change the semantics regarding which data get to the
snapshot, if there are pages being dirtied during the snapshotting
operation.  There's a sync called before snapshot is taken in old/new
case, any IO in flight just after that may be in the snapshot but this
depends on other system effects that might still sync the IO.

We do a simple snapshot speed test on a Intel D-1531 box:

fio --ioengine=libaio --iodepth=32 --bs=4k --rw=write --size=64G
--direct=0 --thread=1 --numjobs=1 --time_based --runtime=120
--filename=/mnt/sub/testfile --name=job1 --group_reporting & sleep 5;
time btrfs sub snap -r /mnt/sub /mnt/snap; killall fio

original: 1m58sec
patched:  6.54sec

This is the best case for this patch since for a sequential write case,
we omit nearly all pages dirtied after the snapshot command.

For a multi writers, random write test:

fio --ioengine=libaio --iodepth=32 --bs=4k --rw=randwrite --size=64G
--direct=0 --thread=1 --numjobs=4 --time_based --runtime=120
--filename=/mnt/sub/testfile --name=job1 --group_reporting & sleep 5;
time btrfs sub snap -r /mnt/sub /mnt/snap; killall fio

original: 15.83sec
patched:  10.35sec

The improvement is smaller compared to the sequential write case,
since we omit only half of the pages dirtied after snapshot command.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Ethan Lien <ethanlien@synology.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2019-02-12 19:47:11 +01:00
..
tests btrfs: qgroup: Drop fs_info parameter from btrfs_qgroup_account_extent 2018-08-06 13:12:52 +02:00
acl.c btrfs: remove unnecessary curly braces in btrfs_get_acl 2018-08-06 13:12:41 +02:00
async-thread.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
async-thread.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
backref.c btrfs: backref: Use ERR_CAST to return error code 2018-08-06 13:13:01 +02:00
backref.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
btrfs_inode.h btrfs: use tagged writepage to mitigate livelock of snapshot 2019-02-12 19:47:11 +01:00
check-integrity.c btrfs: open-code bio_set_op_attrs 2018-08-06 13:12:44 +02:00
check-integrity.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
compression.c btrfs: drop extent_io_ops::merge_bio_hook callback 2018-08-06 13:12:56 +02:00
compression.h btrfs: compression: Add linux/sizes.h for compression.h 2018-05-29 18:13:00 +02:00
ctree.c Btrfs: fix deadlock when allocating tree block during leaf/node split 2019-02-06 17:30:14 +01:00
ctree.h btrfs: use tagged writepage to mitigate livelock of snapshot 2019-02-12 19:47:11 +01:00
dedupe.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
delayed-inode.c btrfs: Remove fs_info from btrfs_delete_delayed_dir_index 2018-08-06 13:13:00 +02:00
delayed-inode.h btrfs: Remove fs_info from btrfs_delete_delayed_dir_index 2018-08-06 13:13:00 +02:00
delayed-ref.c btrfs: Streamline memory allocation failure handling in btrfs_add_delayed_tree_ref 2018-08-06 13:12:39 +02:00
delayed-ref.h btrfs: Remove fs_info from btrfs_add_delayed_data_ref 2018-08-06 13:12:34 +02:00
dev-replace.c btrfs: fix use-after-free due to race between replace start and cancel 2019-01-26 09:32:39 +01:00
dev-replace.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
dir-item.c btrfs: Remove fs_info from btrfs_insert_delayed_dir_index 2018-08-06 13:13:00 +02:00
disk-io.c btrfs: wait on ordered extents on abort cleanup 2019-01-22 21:40:32 +01:00
disk-io.h btrfs: unify end_io callbacks of async_submit_bio 2018-08-06 13:12:55 +02:00
export.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
export.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
extent-tree.c btrfs: run delayed items before dropping the snapshot 2019-01-09 17:38:45 +01:00
extent_io.c btrfs: use tagged writepage to mitigate livelock of snapshot 2019-02-12 19:47:11 +01:00
extent_io.h btrfs: drop extent_io_ops::set_range_writeback callback 2018-08-06 13:12:56 +02:00
extent_map.c btrfs: use fs_info for btrfs_handle_em_exist tracepoint 2018-05-28 18:07:17 +02:00
extent_map.h btrfs: use fs_info for btrfs_handle_em_exist tracepoint 2018-05-28 18:07:17 +02:00
file-item.c btrfs: simplify pointer chasing of local fs_info variables 2018-08-06 13:12:43 +02:00
file.c Btrfs: fix rare chances for data loss when doing a fast fsync 2018-12-05 19:32:06 +01:00
free-space-cache.c Btrfs: fix use-after-free when dumping free space 2018-11-13 11:09:00 -08:00
free-space-cache.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
free-space-tree.c btrfs: Remove fs_info from btrfs_del_root 2018-08-06 13:13:00 +02:00
free-space-tree.h btrfs: Remove fs_info argument from add_to_free_space_tree 2018-05-28 18:07:36 +02:00
inode-item.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
inode-map.c btrfs: prune unused includes 2018-08-06 13:12:43 +02:00
inode-map.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
inode.c btrfs: use tagged writepage to mitigate livelock of snapshot 2019-02-12 19:47:11 +01:00
ioctl.c btrfs: use tagged writepage to mitigate livelock of snapshot 2019-02-12 19:47:11 +01:00
Kconfig btrfs: add SPDX header to Kconfig 2018-04-12 16:29:55 +02:00
locking.c btrfs: replace waitqueue_actvie with cond_wake_up 2018-05-28 18:23:09 +02:00
locking.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
lzo.c btrfs: lzo: Harden inline lzo compressed extent decompression 2018-05-30 16:46:43 +02:00
Makefile btrfs: Remove custom crc32c init code 2018-03-26 15:09:39 +02:00
math.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
ordered-data.c btrfs: prune unused includes 2018-08-06 13:12:43 +02:00
ordered-data.h btrfs: remove remaing full_sync logic from btrfs_sync_file 2018-08-06 13:12:31 +02:00
orphan.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
print-tree.c btrfs: annotate unlikely branches after V0 extent type removal 2018-08-06 13:12:41 +02:00
print-tree.h btrfs: print-tree: debugging output enhancement 2018-04-20 19:18:16 +02:00
props.c btrfs: property: Set incompat flag if lzo/zstd compression is set 2018-05-17 14:18:25 +02:00
props.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
qgroup.c Btrfs: fix deadlock when enabling quotas due to concurrent snapshot creation 2019-01-16 22:04:37 +01:00
qgroup.h btrfs: qgroup: Avoid calling qgroup functions if qgroup is not enabled 2018-11-13 11:08:56 -08:00
raid56.c btrfs: raid56: catch errors from full_stripe_write 2018-08-06 13:12:45 +02:00
raid56.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
rcu-string.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
reada.c btrfs: prune unused includes 2018-08-06 13:12:43 +02:00
ref-verify.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
ref-verify.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
relocation.c btrfs: relocation: set trans to be NULL after ending transaction 2018-12-05 19:32:07 +01:00
root-tree.c btrfs: Remove fs_info from btrfs_add_root_ref 2018-08-06 13:13:00 +02:00
scrub.c btrfs: Use wrapper macro for rcu string to remove duplicate code 2018-08-06 13:13:02 +02:00
send.c Btrfs: send, fix infinite loop due to directory rename dependencies 2018-12-17 09:24:34 +01:00
send.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
struct-funcs.c btrfs: prune unused includes 2018-08-06 13:12:43 +02:00
super.c btrfs: On error always free subvol_name in btrfs_mount 2019-02-06 17:30:14 +01:00
sysfs.c btrfs: prune unused includes 2018-08-06 13:12:43 +02:00
sysfs.h btrfs: sysfs: Use enum/define value for feature array definitions 2018-05-28 18:23:39 +02:00
transaction.c btrfs: don't run delayed_iputs in commit 2018-11-13 11:08:59 -08:00
transaction.h btrfs: replace get_seconds with new 64bit time API 2018-08-06 13:12:29 +02:00
tree-checker.c btrfs: tree-checker: Don't check max block group size as current max chunk size limit is unreliable 2018-12-08 12:59:10 +01:00
tree-checker.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
tree-defrag.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
tree-log.c Btrfs: fix fsync of files with multiple hard links in new directories 2019-01-09 17:38:45 +01:00
tree-log.h Btrfs: sync log after logging new name 2018-08-23 17:37:26 +02:00
ulist.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
ulist.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
uuid-tree.c btrfs: Remove fs_info argument from btrfs_uuid_tree_rem 2018-05-30 16:46:53 +02:00
volumes.c btrfs: harden agaist duplicate fsid on scanned devices 2019-02-12 19:47:10 +01:00
volumes.h btrfs: Introduce mount time chunk <-> dev extent mapping check 2018-08-06 13:13:03 +02:00
xattr.c Btrfs: use nofs context when initializing security xattrs to avoid deadlock 2019-01-16 22:04:37 +01:00
xattr.h btrfs: replace GPL boilerplate by SPDX -- headers 2018-04-12 16:29:46 +02:00
zlib.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00
zstd.c btrfs: replace GPL boilerplate by SPDX -- sources 2018-04-12 16:29:51 +02:00