From: Filipe Manana fdmanana@suse.com
commit 27cdfde181bcacd226c230b2fd831f6f5b8c215f upstream.
When starting a defrag, we should update the writeback index of the inode's mapping in case it currently has a value beyond the start of the range we are defragging. This can help performance and often result in getting less extents after writeback - for e.g., if the current value of the writeback index sits somewhere in the middle of a range that gets dirty by the defrag, then after writeback we can get two smaller extents instead of a single, larger extent.
We used to have this before the refactoring in 5.16, but it was removed without any reason to do so. Originally it was added in kernel 3.1, by commit 2a0f7f5769992b ("Btrfs: fix recursive auto-defrag"), in order to fix a loop with autodefrag resulting in dirtying and writing pages over and over, but some testing on current code did not show that happening, at least with the test described in that commit.
So add back the behaviour, as at the very least it is a nice to have optimization.
Fixes: 7b508037d4cac3 ("btrfs: defrag: use defrag_one_cluster() to implement btrfs_defrag_file()") CC: stable@vger.kernel.org # 5.16 Signed-off-by: Filipe Manana fdmanana@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/ioctl.c | 9 +++++++++ 1 file changed, 9 insertions(+)
--- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -1511,6 +1511,7 @@ int btrfs_defrag_file(struct inode *inod int compress_type = BTRFS_COMPRESS_ZLIB; int ret = 0; u32 extent_thresh = range->extent_thresh; + pgoff_t start_index;
if (isize == 0) return 0; @@ -1552,6 +1553,14 @@ int btrfs_defrag_file(struct inode *inod file_ra_state_init(ra, inode->i_mapping); }
+ /* + * Make writeback start from the beginning of the range, so that the + * defrag range can be written sequentially. + */ + start_index = cur >> PAGE_SHIFT; + if (start_index < inode->i_mapping->writeback_index) + inode->i_mapping->writeback_index = start_index; + while (cur < last_byte) { const unsigned long prev_sectors_defragged = sectors_defragged; u64 cluster_end;