Re: [PATCH v5 00/11] simplify block layer based on immutable biovecs

[Ming Lin <mlin@kernel.org>]

On Mon, 2015-07-06 at 00:11 -0700, mlin@kernel.org wrote:
> Hi Mike,
> 
> On Wed, 2015-06-10 at 17:46 -0400, Mike Snitzer wrote:
> > I've been busy getting DM changes for the 4.2 merge window finalized.
> > As such I haven't connected with others on the team to discuss this
> > issue.
> > 
> > I'll see if we can make time in the next 2 days.  But I also have
> > RHEL-specific kernel deadlines I'm coming up against.
> > 
> > Seems late to be staging this extensive a change for 4.2... are you
> > pushing for this code to land in the 4.2 merge window?  Or do we have
> > time to work this further and target the 4.3 merge?
> > 
> 
> 4.2-rc1 was out.
> Would you have time to work together for 4.3 merge? 

Ping ...

What can I do to move forward?

This patchset not only simplify block layer a lot, it's also a
prerequisite of the direct IO rewrite patches, which I saw 40%
performance improvement for null_blk and 10% improvement for NVMe
drives. I have been fixing bugs for the direct IO patches. I'll post it
once it passes xfstests.

Mike,
Can I have your ACK? Or do you have other test plan?

Thanks,
Ming

> 
> Fio test results(4.1-rc4/rc7) showed no performance regressions
> for HW/SW RAID6 and DM stripe tests.
> http://minggr.net/pub/20150608/fio_results/summary.log
> 
> v5:
>   - rebase on top of 4.2-rc1
>   - reorder patch 6,7
>   - add NeilBrown's ACKs
>   - fix memory leak: free "bio_split" bioset in blk_release_queue()
> 
> v4:
>   - rebase on top of 4.1-rc4
>   - use BIO_POOL_SIZE instead of number 4 for bioset_create()
>   - call blk_queue_split() in blk_mq_make_request()
>   - call blk_queue_split() in zram_make_request()
>   - add patch "block: remove bio_get_nr_vecs()"
>   - remove split code in blkdev_issue_discard()
>   - drop patch "md/raid10: make sync_request_write() call bio_copy_data()".
>     NeilBrown queued it.
>   - drop patch "block: allow __blk_queue_bounce() to handle bios larger than BIO_MAX_PAGES".
>     Will send it seperately
> 
> v3:
>   - rebase on top of 4.1-rc2
>   - support for QUEUE_FLAG_SG_GAPS
>   - update commit logs of patch 2&4
>   - split bio for chunk_aligned_read
> 
> v2: https://lkml.org/lkml/2015/4/28/28
> v1: https://lkml.org/lkml/2014/12/22/128
> 
> This is the 5th attempt of simplifying block layer based on immutable
> biovecs. Immutable biovecs, implemented by Kent Overstreet, have been
> available in mainline since v3.14. Its original goal was actually making
> generic_make_request() accept arbitrarily sized bios, and pushing the
> splitting down to the drivers or wherever it's required. See also
> discussions in the past, [1] [2] [3].
> 
> This will bring not only performance improvements, but also a great amount
> of reduction in code complexity all over the block layer. Performance gain
> is possible due to the fact that bio_add_page() does not have to check
> unnecesary conditions such as queue limits or if biovecs are mergeable.
> Those will be delegated to the driver level. Kent already said that he
> actually benchmarked the impact of this with fio on a micron p320h, which
> showed definitely a positive impact.
> 
> Moreover, this patchset also allows a lot of code to be deleted, mainly
> because of removal of merge_bvec_fn() callbacks. We have been aware that
> it has been always a delicate issue for stacking block drivers (e.g. md
> and bcache) to handle merging bio consistently. This simplication will
> help every individual block driver avoid having such an issue.
> 
> Patches are against 4.2-rc1. These are also available in my git repo at:
> 
>   https://git.kernel.org/cgit/linux/kernel/git/mlin/linux.git/log/?h=block-generic-req
>   git://git.kernel.org/pub/scm/linux/kernel/git/mlin/linux.git block-generic-req
> 
> This patchset is a prerequisite of other consecutive patchsets, e.g.
> multipage biovecs, rewriting plugging, or rewriting direct-IO, which are
> excluded this time. That means, this patchset should not bring any
> regression to end-users.
> 
> Comments are welcome.
> Ming
> 
> [1] https://lkml.org/lkml/2014/11/23/263
> [2] https://lkml.org/lkml/2013/11/25/732
> [3] https://lkml.org/lkml/2014/2/26/618
> 
> Dongsu Park (1):
>       Documentation: update notes in biovecs about arbitrarily sized bios
> 
> Kent Overstreet (8):
>       block: make generic_make_request handle arbitrarily sized bios
>       block: simplify bio_add_page()
>       bcache: remove driver private bio splitting code
>       btrfs: remove bio splitting and merge_bvec_fn() calls
>       md/raid5: get rid of bio_fits_rdev()
>       block: kill merge_bvec_fn() completely
>       fs: use helper bio_add_page() instead of open coding on bi_io_vec
>       block: remove bio_get_nr_vecs()
> 
> Ming Lin (2):
>       block: remove split code in blkdev_issue_discard
>       md/raid5: split bio for chunk_aligned_read
> 
>  Documentation/block/biovecs.txt             |  10 +-
>  block/bio.c                                 | 152 ++++++++++------------------
>  block/blk-core.c                            |  19 ++--
>  block/blk-lib.c                             |  73 +++----------
>  block/blk-merge.c                           | 148 +++++++++++++++++++++++++--
>  block/blk-mq.c                              |   4 +
>  block/blk-settings.c                        |  22 ----
>  block/blk-sysfs.c                           |   3 +
>  drivers/block/drbd/drbd_int.h               |   1 -
>  drivers/block/drbd/drbd_main.c              |   1 -
>  drivers/block/drbd/drbd_req.c               |  37 +------
>  drivers/block/pktcdvd.c                     |  27 +----
>  drivers/block/ps3vram.c                     |   2 +
>  drivers/block/rbd.c                         |  47 ---------
>  drivers/block/rsxx/dev.c                    |   2 +
>  drivers/block/umem.c                        |   2 +
>  drivers/block/zram/zram_drv.c               |   2 +
>  drivers/md/bcache/bcache.h                  |  18 ----
>  drivers/md/bcache/io.c                      | 100 +-----------------
>  drivers/md/bcache/journal.c                 |   4 +-
>  drivers/md/bcache/request.c                 |  16 +--
>  drivers/md/bcache/super.c                   |  32 +-----
>  drivers/md/bcache/util.h                    |   5 +-
>  drivers/md/bcache/writeback.c               |   4 +-
>  drivers/md/dm-cache-target.c                |  21 ----
>  drivers/md/dm-crypt.c                       |  16 ---
>  drivers/md/dm-era-target.c                  |  15 ---
>  drivers/md/dm-flakey.c                      |  16 ---
>  drivers/md/dm-io.c                          |   2 +-
>  drivers/md/dm-linear.c                      |  16 ---
>  drivers/md/dm-log-writes.c                  |  16 ---
>  drivers/md/dm-raid.c                        |  19 ----
>  drivers/md/dm-snap.c                        |  15 ---
>  drivers/md/dm-stripe.c                      |  21 ----
>  drivers/md/dm-table.c                       |   8 --
>  drivers/md/dm-thin.c                        |  31 ------
>  drivers/md/dm-verity.c                      |  16 ---
>  drivers/md/dm.c                             | 129 +----------------------
>  drivers/md/dm.h                             |   2 -
>  drivers/md/linear.c                         |  43 --------
>  drivers/md/md.c                             |  28 +----
>  drivers/md/md.h                             |  12 ---
>  drivers/md/multipath.c                      |  21 ----
>  drivers/md/raid0.c                          |  56 ----------
>  drivers/md/raid0.h                          |   2 -
>  drivers/md/raid1.c                          |  58 +----------
>  drivers/md/raid10.c                         | 121 +---------------------
>  drivers/md/raid5.c                          |  92 ++++++-----------
>  drivers/s390/block/dcssblk.c                |   2 +
>  drivers/s390/block/xpram.c                  |   2 +
>  drivers/staging/lustre/lustre/llite/lloop.c |   2 +
>  fs/btrfs/compression.c                      |   5 +-
>  fs/btrfs/extent_io.c                        |   9 +-
>  fs/btrfs/inode.c                            |   3 +-
>  fs/btrfs/scrub.c                            |  18 +---
>  fs/btrfs/volumes.c                          |  72 -------------
>  fs/buffer.c                                 |   7 +-
>  fs/direct-io.c                              |   2 +-
>  fs/ext4/page-io.c                           |   3 +-
>  fs/ext4/readpage.c                          |   2 +-
>  fs/f2fs/data.c                              |   2 +-
>  fs/gfs2/lops.c                              |   9 +-
>  fs/jfs/jfs_logmgr.c                         |  14 +--
>  fs/logfs/dev_bdev.c                         |   4 +-
>  fs/mpage.c                                  |   4 +-
>  fs/nilfs2/segbuf.c                          |   2 +-
>  fs/xfs/xfs_aops.c                           |   3 +-
>  include/linux/bio.h                         |   1 -
>  include/linux/blkdev.h                      |  13 +--
>  include/linux/device-mapper.h               |   4 -
>  mm/page_io.c                                |   8 +-
>  71 files changed, 340 insertions(+), 1358 deletions(-)