diff options
author | Qu Wenruo <wqu@suse.com> | 2022-02-08 13:31:19 +0800 |
---|---|---|
committer | David Sterba <dsterba@suse.com> | 2022-03-14 13:13:50 +0100 |
commit | 40e7efe057ae7446915dc9d95bbfe4c6c7329d89 (patch) | |
tree | d445ab3ec50bae29f76676eba32298b1112e6755 /fs/btrfs/file-item.c | |
parent | 6d3b050efa079f5bc4d5e2a8f37f0dc0345a2096 (diff) |
btrfs: populate extent_map::generation when reading from disk
When btrfs_get_extent() tries to get some file extent from disk, it
never populates extent_map::generation, leaving the value to be 0.
On the other hand, for extent map generated by IO, it will get its
generation properly set at finish_ordered_io()
finish_ordered_io()
|- unpin_extent_cache(gen = trans->transid)
|- em->generation = gen;
[CAUSE]
Since extent_map::generation is mostly used by fsync code, and for fsync
they only care about modified extents, which all have their
em::generation > 0.
Thus it's fine to not populate em read from disk for fsync.
[CORNER CASE]
However autodefrag also relies on em::generation to determine if one
extent needs to be defragged.
This unpopulated extent_map::generation can prevent the following
autodefrag case from working:
mkfs.btrfs -f $dev
mount $dev $mnt -o autodefrag
# initial write to queue the inode for autodefrag
xfs_io -f -c "pwrite 0 4k" $mnt/file
sync
# Real fragmented write
xfs_io -f -s -c "pwrite -b 4096 0 32k" $mnt/file
sync
echo "=== before autodefrag ==="
xfs_io -c "fiemap -v" $mnt/file
# Drop cache to force em to be read from disk
echo 3 > /proc/sys/vm/drop_caches
mount -o remount,commit=1 $mnt
sleep 3
sync
echo "=== After autodefrag ==="
xfs_io -c "fiemap -v" $mnt/file
umount $mnt
The result looks like this:
=== before autodefrag ===
/mnt/btrfs/file:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..15]: 26672..26687 16 0x0
1: [16..31]: 26656..26671 16 0x0
2: [32..47]: 26640..26655 16 0x0
3: [48..63]: 26624..26639 16 0x1
=== After autodefrag ===
/mnt/btrfs/file:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..15]: 26672..26687 16 0x0
1: [16..31]: 26656..26671 16 0x0
2: [32..47]: 26640..26655 16 0x0
3: [48..63]: 26624..26639 16 0x1
This fragmented 32K will not be defragged by autodefrag.
[FIX]
To make things less weird, just populate extent_map::generation when
reading file extents from disk.
This would make above fragmented extents to be properly defragged:
== before autodefrag ===
/mnt/btrfs/file:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..15]: 26672..26687 16 0x0
1: [16..31]: 26656..26671 16 0x0
2: [32..47]: 26640..26655 16 0x0
3: [48..63]: 26624..26639 16 0x1
=== After autodefrag ===
/mnt/btrfs/file:
EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS
0: [0..63]: 26688..26751 64 0x1
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs/file-item.c')
-rw-r--r-- | fs/btrfs/file-item.c | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c index 90c5c38836ab..9a3de652ada8 100644 --- a/fs/btrfs/file-item.c +++ b/fs/btrfs/file-item.c @@ -1211,6 +1211,7 @@ void btrfs_extent_item_to_extent_map(struct btrfs_inode *inode, extent_start = key.offset; extent_end = btrfs_file_extent_end(path); em->ram_bytes = btrfs_file_extent_ram_bytes(leaf, fi); + em->generation = btrfs_file_extent_generation(leaf, fi); if (type == BTRFS_FILE_EXTENT_REG || type == BTRFS_FILE_EXTENT_PREALLOC) { em->start = extent_start; |