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| author | Ethan Lien | 2018-11-01 07:49:03 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman | 2019-02-12 19:47:11 +0100 |
| commit | f5d5b54349125f4765b51153960676ea4d81b82b (patch) | |
| tree | f581137536914c2f1ce35f7b42142e383ea6625e /fs/btrfs/btrfs_inode.h | |
| parent | perf header: Fix unchecked usage of strncpy() (diff) | |
| download | kernel-qcow2-linux-f5d5b54349125f4765b51153960676ea4d81b82b.tar.gz kernel-qcow2-linux-f5d5b54349125f4765b51153960676ea4d81b82b.tar.xz kernel-qcow2-linux-f5d5b54349125f4765b51153960676ea4d81b82b.zip | |
btrfs: use tagged writepage to mitigate livelock of snapshot
[ Upstream commit 3cd24c698004d2f7668e0eb9fc1f096f533c791b ]
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>
Diffstat (limited to 'fs/btrfs/btrfs_inode.h')
| -rw-r--r-- | fs/btrfs/btrfs_inode.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h index 7177d1d33584..45f5cf9cd203 100644 --- a/fs/btrfs/btrfs_inode.h +++ b/fs/btrfs/btrfs_inode.h @@ -29,6 +29,7 @@ enum { BTRFS_INODE_IN_DELALLOC_LIST, BTRFS_INODE_READDIO_NEED_LOCK, BTRFS_INODE_HAS_PROPS, + BTRFS_INODE_SNAPSHOT_FLUSH, }; /* in memory btrfs inode */ |