Commit 68bb462d authored Apr 01, 2014 by Wang Shilong Committed by Chris Mason Apr 07, 2014

Btrfs: don't compress for a small write



To compress a small file range(<=blocksize) that is not
an inline extent can not save disk space at all. skip it can
save us some cpu time.

This patch can also fix wrong setting nocompression flag for
inode, say a case when @total_in is 4096, and then we get
@total_compressed 52,because we do aligment to page cache size
firstly, and then we get into conclusion @total_in=@total_compressed
thus we will clear this inode's compression flag.

An exception comes from inserting inline extent failure but we
still have @total_compressed < @total_in,so we will still reset
inode's flag, this is ok, because we don't have good compression
effect.

Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

parent c50d3e71

fs/btrfs/inode.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -394,6 +394,14 @@ 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;

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