This is the second 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] [4]. 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. - Patch 01/09 allows generic_make_request handle arbitrarily sized bios, by making make_request functions call blk_queue_split(). - Patch 02/09 simplifies __bio_add_page() to avoid calling ->merge_bvec_fn(). - Patch 03/09 allows queue_bounce to handle bios with > BIO_MAX_PAGES - Patch 04/09 gets rid of workarounds in bcache. - Patch 05/09 removes unnecessary biovec merging parts in btrfs - Patch 06/09 removes unnecessary biovec merging parts in MD-RAID5. - Patch 07/09 removes ->merge_bvec_fn() completely, which affects a lot of block drivers, such as Ceph RBD, DRBD, device mapper, MD, etc. - Patch 08/09 makes filesystems use helper bio_add_page(). - Patch 09/09 updates document about biovecs.
Patches are against 3.19-rc4. These are also available in my git repo at: https://github.com/dongsupark/linux.git block-generic-req It's recommended to apply this patchset on top of its preparation patchset i.e. "preparation for block layer simplification". [5] This patchset is in turn also a prerequisite of other consecutive patchsets, e.g. multipage biovecs, rewriting plugging, or rewriting direct-IO, which is yet to-be-done. This patchset should not bring any regression to end-users. I already tested it with xfstests multiple times. On the other hand, the multipage biovecs part is currently in heavy development, with help of Kent and Ming Lin. Those experimental patches are also available on other branches on my git tree. Once they are done, I'm also going to post them to get reviews. Comments are welcome. Dongsu Changes in v2: - split up preparation patches into a separate series - remove a patch "block: simplify issueing discard, write_same, zeroout", as suggested by Christoph Hellwig. - move a patch "btrfs: make use of immutable biovecs" to the upcoming series. - minor change in ps3vram suggested by Geoff Levand - make bio_add_page() warn once on a cloned bio. - add more comments and commit messages to patch 02 "block: simplify bio_add_page()" [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 [4] https://lkml.org/lkml/2014/12/22/128 [5] https://lkml.org/lkml/2015/1/12/255 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() block: allow __blk_queue_bounce() to handle bios larger than BIO_MAX_PAGES bcache: clean up hacks around bio_split_pool 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 Documentation/block/biovecs.txt | 10 +- block/bio.c | 135 +++++++++++---------------- block/blk-core.c | 19 ++-- block/blk-merge.c | 140 ++++++++++++++++++++++++++-- block/blk-mq.c | 2 + block/blk-settings.c | 22 ----- block/bounce.c | 60 ++++++++++-- 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-linear.c | 16 ---- 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 | 122 +----------------------- drivers/md/dm.h | 2 - drivers/md/linear.c | 46 --------- drivers/md/md.c | 4 +- drivers/md/md.h | 8 -- drivers/md/multipath.c | 21 ----- drivers/md/raid0.c | 57 ----------- drivers/md/raid0.h | 2 - drivers/md/raid1.c | 59 +----------- drivers/md/raid10.c | 122 +----------------------- drivers/md/raid5.c | 51 +--------- drivers/s390/block/dcssblk.c | 2 + drivers/s390/block/xpram.c | 2 + drivers/staging/lustre/lustre/llite/lloop.c | 2 + fs/btrfs/volumes.c | 73 --------------- fs/buffer.c | 7 +- fs/jfs/jfs_logmgr.c | 14 +-- include/linux/blkdev.h | 13 +-- include/linux/device-mapper.h | 4 - mm/page_io.c | 8 +- 53 files changed, 318 insertions(+), 1164 deletions(-) -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
