Re: [PATCH 0/9] btrfs: more optimizations for lseek and fiemap

[Wang Yugui <wangyugui@e16-tech.com>]

Hi,

> From: Filipe Manana <fdmanana@suse.com>
> 
> Here follows a few more optimizations for lseek and fiemap. Starting with
> coreutils 9.0, cp no longer uses fiemap to determine where holes are in a
> file, instead it uses lseek's SEEK_HOLE and SEEK_DATA modes of operation.
> For very sparse files, or files with lot of delalloc, this can be very
> slow (when compared to ext4 or xfs). This aims to improve that.
> 
> The cp pattern is not specific to cp, it's common to iterate over all
> allocated regions of a file sequentially with SEEK_HOLE and SEEK_DATA,
> for either the whole file or just a section. Another popular program that
> does the same is tar, when using its --sparse / -S command line option
> (I use it like that for doing vm backups for example).

The case reported in *1 is huge improved. Thanks a lot.
*1 
https://lore.kernel.org/linux-btrfs/20221106073028.71F9.409509F4@e16-tech.com/

and btrfs misc-next with these patches passed fstests too.

Best Regards
Wang Yugui (wangyugui@e16-tech.com)
2022/11/12

> The details are in the changelogs of each patch, and results are on the
> changelog of the last patch in the series. There's still much more room
> for further improvement, but that won't happen too soon as it will require
> broader changes outside the lseek and fiemap code.
> 
> Filipe Manana (9):
>   btrfs: remove leftover setting of EXTENT_UPTODATE state in an inode's io_tree
>   btrfs: add an early exit when searching for delalloc range for lseek/fiemap
>   btrfs: skip unnecessary delalloc searches during lseek/fiemap
>   btrfs: search for delalloc more efficiently during lseek/fiemap
>   btrfs: remove no longer used btrfs_next_extent_map()
>   btrfs: allow passing a cached state record to count_range_bits()
>   btrfs: update stale comment for count_range_bits()
>   btrfs: use cached state when looking for delalloc ranges with fiemap
>   btrfs: use cached state when looking for delalloc ranges with lseek
> 
>  fs/btrfs/ctree.h          |   1 +
>  fs/btrfs/extent-io-tree.c |  73 +++++++++++--
>  fs/btrfs/extent-io-tree.h |  10 +-
>  fs/btrfs/extent_io.c      |  30 +++---
>  fs/btrfs/extent_map.c     |  29 -----
>  fs/btrfs/extent_map.h     |   2 -
>  fs/btrfs/file.c           | 221 ++++++++++++++++++--------------------
>  fs/btrfs/file.h           |   1 +
>  fs/btrfs/inode.c          |   2 +-
>  9 files changed, 190 insertions(+), 179 deletions(-)
> 
> -- 
> 2.35.1