[Drbd-dev] [PATCH 00/60] block: support multipage bvec

[Drbd-dev] [PATCH 00/60] block: support multipage bvec

[Ming Lei]

Hi,

This patchset brings multipage bvec into block layer. Basic
xfstests(-a auto) over virtio-blk/virtio-scsi have been run
and no regression is found, so it should be good enough
to show the approach now, and any comments are welcome!

1) what is multipage bvec?

Multipage bvecs means that one 'struct bio_bvec' can hold
multiple pages which are physically contiguous instead
of one single page used in linux kernel for long time.

2) why is multipage bvec introduced?

Kent proposed the idea[1] first. 

As system's RAM becomes much bigger than before, and 
at the same time huge page, transparent huge page and
memory compaction are widely used, it is a bit easy now
to see physically contiguous pages inside fs/block stack.
On the other hand, from block layer's view, it isn't
necessary to store intermediate pages into bvec, and
it is enough to just store the physicallly contiguous
'segment'.

Also huge pages are being brought to filesystem[2], we
can do IO a hugepage a time[3], requires that one bio can
transfer at least one huge page one time. Turns out it isn't
flexiable to change BIO_MAX_PAGES simply[3]. Multipage bvec
can fit in this case very well.

With multipage bvec:

- bio size can be increased and it should improve some
high-bandwidth IO case in theory[4].

- Inside block layer, both bio splitting and sg map can
become more efficient than before by just traversing the
physically contiguous 'segment' instead of each page.

- there is possibility in future to improve memory footprint
of bvecs usage. 

3) how is multipage bvec implemented in this patchset?

The 1st 22 patches cleanup on direct access to bvec table,
and comments on some special cases. With this approach,
most of cases are found as safe for multipage bvec,
only fs/buffer, pktcdvd, dm-io, MD and btrfs need to deal
with.

Given a little more work is involved to cleanup pktcdvd,
MD and btrfs, this patchset introduces QUEUE_FLAG_NO_MP for
them, and these components can still see/use singlepage bvec.
In the future, once the cleanup is done, the flag can be killed.

The 2nd part(23 ~ 60) implements multipage bvec in block:

- put all tricks into bvec/bio/rq iterators, and as far as
drivers and fs use these standard iterators, they are happy
with multipage bvec

- bio_for_each_segment_all() changes
this helper pass pointer of each bvec directly to user, and
it has to be changed. Two new helpers(bio_for_each_segment_all_rd()
and bio_for_each_segment_all_wt()) are introduced. 

- bio_clone() changes
At default bio_clone still clones one new bio in multipage bvec
way. Also single page version of bio_clone() is introduced
for some special cases, such as only single page bvec is used
for the new cloned bio(bio bounce, ...)

These patches can be found in the following git tree:

	https://github.com/ming1/linux/tree/mp-bvec-0.3-v4.9

Thanks Christoph for looking at the early version and providing
very good suggestions, such as: introduce bio_init_with_vec_table(),
remove another unnecessary helpers for cleanup and so on.

TODO:
	- cleanup direct access to bvec table for MD & btrfs


[1], http://marc.info/?l=linux-kernel&m=141680246629547&w=2
[2], http://lwn.net/Articles/700781/
[3], http://marc.info/?t=147735447100001&r=1&w=2
[4], http://marc.info/?l=linux-mm&m=147745525801433&w=2


Ming Lei (60):
  block: bio: introduce bio_init_with_vec_table()
  block drivers: convert to bio_init_with_vec_table()
  block: drbd: remove impossible failure handling
  block: floppy: use bio_add_page()
  target: avoid to access .bi_vcnt directly
  bcache: debug: avoid to access .bi_io_vec directly
  dm: crypt: use bio_add_page()
  dm: use bvec iterator helpers to implement .get_page and .next_page
  dm: dm.c: replace 'bio->bi_vcnt == 1' with !bio_multiple_segments
  fs: logfs: convert to bio_add_page() in sync_request()
  fs: logfs: use bio_add_page() in __bdev_writeseg()
  fs: logfs: use bio_add_page() in do_erase()
  fs: logfs: remove unnecesary check
  block: drbd: comment on direct access bvec table
  block: loop: comment on direct access to bvec table
  block: pktcdvd: comment on direct access to bvec table
  kernel/power/swap.c: comment on direct access to bvec table
  mm: page_io.c: comment on direct access to bvec table
  fs/buffer: comment on direct access to bvec table
  f2fs: f2fs_read_end_io: comment on direct access to bvec table
  bcache: comment on direct access to bvec table
  block: comment on bio_alloc_pages()
  block: introduce flag QUEUE_FLAG_NO_MP
  md: set NO_MP for request queue of md
  block: pktcdvd: set NO_MP for pktcdvd request queue
  btrfs: set NO_MP for request queues behind BTRFS
  block: introduce BIO_SP_MAX_SECTORS
  block: introduce QUEUE_FLAG_SPLIT_MP
  dm: limit the max bio size as BIO_SP_MAX_SECTORS << SECTOR_SHIFT
  bcache: set flag of QUEUE_FLAG_SPLIT_MP
  block: introduce multipage/single page bvec helpers
  block: implement sp version of bvec iterator helpers
  block: introduce bio_for_each_segment_mp()
  block: introduce bio_clone_sp()
  bvec_iter: introduce BVEC_ITER_ALL_INIT
  block: bounce: avoid direct access to bvec from bio->bi_io_vec
  block: bounce: don't access bio->bi_io_vec in copy_to_high_bio_irq
  block: bounce: convert multipage bvecs into singlepage
  bcache: debug: switch to bio_clone_sp()
  blk-merge: compute bio->bi_seg_front_size efficiently
  block: blk-merge: try to make front segments in full size
  block: use bio_for_each_segment_mp() to compute segments count
  block: use bio_for_each_segment_mp() to map sg
  block: introduce bvec_for_each_sp_bvec()
  block: bio: introduce bio_for_each_segment_all_rd() and its write pair
  block: deal with dirtying pages for multipage bvec
  block: convert to bio_for_each_segment_all_rd()
  fs/mpage: convert to bio_for_each_segment_all_rd()
  fs/direct-io: convert to bio_for_each_segment_all_rd()
  ext4: convert to bio_for_each_segment_all_rd()
  xfs: convert to bio_for_each_segment_all_rd()
  logfs: convert to bio_for_each_segment_all_rd()
  gfs2: convert to bio_for_each_segment_all_rd()
  f2fs: convert to bio_for_each_segment_all_rd()
  exofs: convert to bio_for_each_segment_all_rd()
  fs: crypto: convert to bio_for_each_segment_all_rd()
  bcache: convert to bio_for_each_segment_all_rd()
  dm-crypt: convert to bio_for_each_segment_all_rd()
  fs/buffer.c: use bvec iterator to truncate the bio
  block: enable multipage bvecs

 block/bio.c                        | 104 ++++++++++++++----
 block/blk-merge.c                  | 216 +++++++++++++++++++++++++++++--------
 block/bounce.c                     |  80 ++++++++++----
 drivers/block/drbd/drbd_bitmap.c   |   1 +
 drivers/block/drbd/drbd_receiver.c |  14 +--
 drivers/block/floppy.c             |  10 +-
 drivers/block/loop.c               |   5 +
 drivers/block/pktcdvd.c            |   8 ++
 drivers/md/bcache/btree.c          |   4 +-
 drivers/md/bcache/debug.c          |  19 +++-
 drivers/md/bcache/io.c             |   4 +-
 drivers/md/bcache/journal.c        |   4 +-
 drivers/md/bcache/movinggc.c       |   7 +-
 drivers/md/bcache/super.c          |  25 +++--
 drivers/md/bcache/util.c           |   7 ++
 drivers/md/bcache/writeback.c      |   6 +-
 drivers/md/dm-bufio.c              |   4 +-
 drivers/md/dm-crypt.c              |  11 +-
 drivers/md/dm-io.c                 |  34 ++++--
 drivers/md/dm-rq.c                 |   3 +-
 drivers/md/dm.c                    |  11 +-
 drivers/md/md.c                    |  12 +++
 drivers/md/raid5.c                 |   9 +-
 drivers/nvme/target/io-cmd.c       |   4 +-
 drivers/target/target_core_pscsi.c |   8 +-
 fs/btrfs/volumes.c                 |   3 +
 fs/buffer.c                        |  24 +++--
 fs/crypto/crypto.c                 |   3 +-
 fs/direct-io.c                     |   4 +-
 fs/exofs/ore.c                     |   3 +-
 fs/exofs/ore_raid.c                |   3 +-
 fs/ext4/page-io.c                  |   3 +-
 fs/ext4/readpage.c                 |   3 +-
 fs/f2fs/data.c                     |  13 ++-
 fs/gfs2/lops.c                     |   3 +-
 fs/gfs2/meta_io.c                  |   3 +-
 fs/logfs/dev_bdev.c                | 110 +++++++------------
 fs/mpage.c                         |   3 +-
 fs/xfs/xfs_aops.c                  |   3 +-
 include/linux/bio.h                | 108 +++++++++++++++++--
 include/linux/blk_types.h          |   6 ++
 include/linux/blkdev.h             |   4 +
 include/linux/bvec.h               | 123 +++++++++++++++++++--
 kernel/power/swap.c                |   2 +
 mm/page_io.c                       |   1 +
 45 files changed, 759 insertions(+), 276 deletions(-)

-- 
2.7.4

[Drbd-dev] [PATCH 03/60] block: drbd: remove impossible failure handling

[Ming Lei]

For a non-cloned bio, bio_add_page() only returns failure when
the io vec table is full, but in that case, bio->bi_vcnt can't
be zero at all.

So remove the impossible failure handling.

Acked-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
---
 drivers/block/drbd/drbd_receiver.c | 14 +-------------
 1 file changed, 1 insertion(+), 13 deletions(-)

diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 942384f34e22..c537e3bd09eb 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -1648,20 +1648,8 @@ int drbd_submit_peer_request(struct drbd_device *device,
 
 	page_chain_for_each(page) {
 		unsigned len = min_t(unsigned, data_size, PAGE_SIZE);
-		if (!bio_add_page(bio, page, len, 0)) {
-			/* A single page must always be possible!
-			 * But in case it fails anyways,
-			 * we deal with it, and complain (below). */
-			if (bio->bi_vcnt == 0) {
-				drbd_err(device,
-					"bio_add_page failed for len=%u, "
-					"bi_vcnt=0 (bi_sector=%llu)\n",
-					len, (uint64_t)bio->bi_iter.bi_sector);
-				err = -ENOSPC;
-				goto fail;
-			}
+		if (!bio_add_page(bio, page, len, 0))
 			goto next_bio;
-		}
 		data_size -= len;
 		sector += len >> 9;
 		--nr_pages;
-- 
2.7.4

Re: [Drbd-dev] [PATCH 03/60] block: drbd: remove impossible failure handling

[Christoph Hellwig]

On Sat, Oct 29, 2016 at 04:08:02PM +0800, Ming Lei wrote:
> For a non-cloned bio, bio_add_page() only returns failure when
> the io vec table is full, but in that case, bio->bi_vcnt can't
> be zero at all.
> 
> So remove the impossible failure handling.
> 
> Acked-by: Lars Ellenberg <lars.ellenberg@linbit.com>
> Signed-off-by: Ming Lei <tom.leiming@gmail.com>

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

[Drbd-dev] [PATCH 14/60] block: drbd: comment on direct access bvec table

[Ming Lei]

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
---
 drivers/block/drbd/drbd_bitmap.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/block/drbd/drbd_bitmap.c b/drivers/block/drbd/drbd_bitmap.c
index ab62b81c2ca7..ce9506da30ad 100644
--- a/drivers/block/drbd/drbd_bitmap.c
+++ b/drivers/block/drbd/drbd_bitmap.c
@@ -953,6 +953,7 @@ static void drbd_bm_endio(struct bio *bio)
 	struct drbd_bm_aio_ctx *ctx = bio->bi_private;
 	struct drbd_device *device = ctx->device;
 	struct drbd_bitmap *b = device->bitmap;
+	/* single page bio, safe for multipage bvec */
 	unsigned int idx = bm_page_to_idx(bio->bi_io_vec[0].bv_page);
 
 	if ((ctx->flags & BM_AIO_COPY_PAGES) == 0 &&
-- 
2.7.4

Re: [Drbd-dev] [PATCH 00/60] block: support multipage bvec

[Christoph Hellwig]

Hi Ming,

can you send a first patch just doing the obvious cleanups like
converting to bio_add_page and replacing direct poking into the
bio with the proper accessors?  That should help reducing the
actual series to a sane size, and it should also help to cut
down the Cc list.

Re: [Drbd-dev] [PATCH 00/60] block: support multipage bvec

[Ming Lei]

On Mon, Oct 31, 2016 at 11:25 PM, Christoph Hellwig <hch@infradead.org> wrote:
> Hi Ming,
>
> can you send a first patch just doing the obvious cleanups like
> converting to bio_add_page and replacing direct poking into the
> bio with the proper accessors?  That should help reducing the

OK, that is just the 1st part of the patchset.

> actual series to a sane size, and it should also help to cut
> down the Cc list.
>



Thanks,
Ming Lei