Btrfs: fix incorrect compression ratio detection (4bcbb332) · Commits · 戴 / test

Steps to reproduce: # mkfs.btrfs -f /dev/sdb # mount -t btrfs /dev/sdb /mnt -o compress=lzo # dd if=/dev/zero of=/mnt/data bs=$((33*4096)) count=1 after previous steps, inode will be detected as bad compression ratio, and NOCOMPRESS flag will be set for that inode. Reason is that compress have a max limit pages every time(128K), if a 132k write in, it will be splitted into two write(128k+4k), this bug is a leftover for commit (Btrfs: don't compress for a small write) Fix this problem by checking every time before compression, if it is a small write(<=blocksize), we bail out and fall into nocompression directly. Signed-off-by:

Wang Shilong <wangshilong1991@gmail.com> Reviewed-by:

Miao Xie <miaox@cn.fujitsu.com> Signed-off-by:

Chris Mason <clm@fb.com>

fs/btrfs/inode.c

+8 −8

Original line number	Diff line number	Diff line
		@@ -411,14 +411,6 @@ static noinline int compress_file_range(struct inode *inode,
		(start > 0 \|\| end + 1 < BTRFS_I(inode)->disk_i_size))
		btrfs_add_inode_defrag(NULL, inode);

		/*
		* skip compression for a small file range(<=blocksize) that
		* isn't an inline extent, since it dosen't save disk space at all.
		*/
		if ((end - start + 1) <= blocksize &&
		(start > 0 \|\| end + 1 < BTRFS_I(inode)->disk_i_size))
		goto cleanup_and_bail_uncompressed;

		actual_end = min_t(u64, isize, end + 1);
		again:
		will_compress = 0;
		@@ -440,6 +432,14 @@ again:

		total_compressed = actual_end - start;

		/*
		* skip compression for a small file range(<=blocksize) that
		* isn't an inline extent, since it dosen't save disk space at all.
		*/
		if (total_compressed <= blocksize &&
		(start > 0 \|\| end + 1 < BTRFS_I(inode)->disk_i_size))
		goto cleanup_and_bail_uncompressed;

		/* we want to make sure that amount of ram required to uncompress
		* an extent is reasonable, so we limit the total size in ram
		* of a compressed extent to 128k. This is a crucial number

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