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

mlin
2015-07-06T07:11:39Z

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?

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(-)