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authorQu Wenruo <wqu@suse.com>2022-02-08 13:31:19 +0800
committerDavid Sterba <dsterba@suse.com>2022-03-14 13:13:50 +0100
commit40e7efe057ae7446915dc9d95bbfe4c6c7329d89 (patch)
treed445ab3ec50bae29f76676eba32298b1112e6755 /fs/btrfs/file-item.c
parent6d3b050efa079f5bc4d5e2a8f37f0dc0345a2096 (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.c1
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;