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btrfs: reject single block sized compression early

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Currently for an inode that needs compression, even if there is a delalloc
range that is single fs block sized and can not be inlined, we will
still go through the compression path.

Then inside compress_file_range(), we have one extra check to reject
single block sized range, and fall back to regular uncompressed write.

This rejection is in fact a little too late, we have already allocated
memory to async_chunk, delayed the submission, just to fallback to the
same uncompressed write.

Change the behavior to reject such cases earlier at
inode_need_compress(), so for such single block sized range we won't
even bother trying to go through compress path.

And since the inline small block check is inside inode_need_compress()
and compress_file_range() also calls that function, we no longer need a
dedicate check inside compress_file_range().

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Qu Wenruo
2026-01-06 13:20:30 +10:30
committed by David Sterba
parent d6f6109fe4
commit 59615e2c1f
1 changed files with 8 additions and 12 deletions
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20
fs/btrfs/inode.c
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@@ -816,6 +816,13 @@ static inline int inode_need_compress(struct btrfs_inode *inode, u64 start,
return 0;
}
/*
* If the delalloc range is only one fs block and can not be inlined,
* do not even bother try compression, as there will be no space saving
* and will always fallback to regular write later.
*/
if (start != 0 && end + 1 - start <= fs_info->sectorsize)
return 0;
/* Defrag ioctl takes precedence over mount options and properties. */
if (inode->defrag_compress == BTRFS_DEFRAG_DONT_COMPRESS)
return 0;
@@ -953,18 +960,7 @@ static void compress_file_range(struct btrfs_work *work)
if (actual_end <= start)
goto cleanup_and_bail_uncompressed;
total_compressed = actual_end - start;
/*
* Skip compression for a small file range(<=blocksize) that
* isn't an inline extent, since it doesn't save disk space at all.
*/
if (total_compressed <= blocksize &&
(start > 0 || end + 1 < inode->disk_i_size))
goto cleanup_and_bail_uncompressed;
total_compressed = min_t(unsigned long, total_compressed,
BTRFS_MAX_UNCOMPRESSED);
total_compressed = min_t(unsigned long, actual_end - start, BTRFS_MAX_UNCOMPRESSED);
total_in = 0;
ret = 0;