Re: bcachefs-for-review

[Oleksandr Natalenko]

Hi.

On 27.10.2020 21:04, Kent Overstreet wrote:
> Here's where bcachefs is at and what I'd like to get merged:
>
> https://evilpiepirate.org/git/bcachefs.git/log/?h=bcachefs-for-review

Please excuse my ignorance if I missed things in other discussions, but 
if this is what's expected to be reviewed, why the submission is not 
splitted into reviewable patches?

> Non bcachefs prep patches:
>
>       Compiler Attributes: add __flatten
>       locking: SIX locks (shared/intent/exclusive)
>       mm: export find_get_pages_range()
>       mm: Add a mechanism to disable faults for a specific mapping
>       mm: Bring back vmalloc_exec
>       fs: insert_inode_locked2()
>       fs: factor out d_mark_tmpfile()
>       block: Add some exports for bcachefs
>       block: Add blk_status_to_str()
>       bcache: move closures to lib/
>       closures: closure_wait_event()
>
>  block/bio.c                                    |   2 +
>  block/blk-core.c                               |  13 +-
>  drivers/md/bcache/Kconfig                      |  10 +-
>  drivers/md/bcache/Makefile                     |   4 +-
>  drivers/md/bcache/bcache.h                     |   2 +-
>  drivers/md/bcache/super.c                      |   1 -
>  drivers/md/bcache/util.h                       |   3 +-
>  fs/dcache.c                                    |  10 +-
>  fs/inode.c                                     |  40 ++
>  include/linux/blkdev.h                         |   1 +
>  {drivers/md/bcache => include/linux}/closure.h |  39 +-
>  include/linux/compiler_attributes.h            |   5 +
>  include/linux/dcache.h                         |   1 +
>  include/linux/fs.h                             |   1 +
>  include/linux/sched.h                          |   1 +
>  include/linux/six.h                            | 197 +++++++++
>  include/linux/vmalloc.h                        |   1 +
>  init/init_task.c                               |   1 +
>  kernel/Kconfig.locks                           |   3 +
>  kernel/locking/Makefile                        |   1 +
>  kernel/locking/six.c                           | 553 
> +++++++++++++++++++++++++
>  kernel/module.c                                |   4 +-
>  lib/Kconfig                                    |   3 +
>  lib/Kconfig.debug                              |   9 +
>  lib/Makefile                                   |   2 +
>  {drivers/md/bcache => lib}/closure.c           |  35 +-
>  mm/filemap.c                                   |   1 +
>  mm/gup.c                                       |   7 +
>  mm/nommu.c                                     |  18 +
>  mm/vmalloc.c                                   |  21 +
>  30 files changed, 937 insertions(+), 52 deletions(-)
>  rename {drivers/md/bcache => include/linux}/closure.h (94%)
>  create mode 100644 include/linux/six.h
>  create mode 100644 kernel/locking/six.c
>  rename {drivers/md/bcache => lib}/closure.c (89%)
>
> New since last posting that's relevant to the rest of the kernel:
>  - Re: the DIO cache coherency issue, we finally have a solution that 
> hopefully
>    everyone will find palatable. We no longer try to do any fancy 
> recursive
>    locking stuff: if userspace issues a DIO read/write where the buffer 
> points
>    to the same address space as the file being read/written to, we just 
> return
>    an error.
>
>    This requires a small change to gup.c, to add the check after the 
> VMA lookup.
>    My patch passes the mapping to check against via a new task_struct 
> member,
>    which is ugly because plumbing a new argument all the way to 
> __get_user_pages
>    is also going to be ugly and if I have to do that I'm likely to go 
> on a
>    refactoring binge, which gup.c looks like it needs anyways.
>
>  - vmalloc_exec() is needed because bcachefs dynamically generates x86 
> machine
>    code - per btree node unpack functions.
>
> Bcachefs changes since last posting:
>  - lots
>  - reflink is done
>  - erasure coding (reed solomon raid5/6) is maturing; I have declared 
> it ready
>    for beta testers and gotten some _very_ positive feedback on its 
> performance.
>  - btree key cache code is done and merged, big improvements to 
> multithreaded
>    write workloads
>  - inline data extents
>  - major improvements to how the btree code handles extents (still 
> todo:
>    re-implement extent merging)
>  - huge improvements to mount/unmount times on huge filesystems
>  - many, many bugfixes; bug reports are slowing and the bugs that are 
> being
>    reported look less and less concerning. In particular repair code is 
> getting
>    better and more polished.
>
> TODO:
>  - scrub, repair of replicated data when one of the replicas fail the 
> checksum
>    check
>  - erasure coding needs repair code (it'll do reconstruct reads, but we 
> don't
>    have code to rewrite bad blocks in a stripe yet. this is going to be 
> a hassle
>    until we get backpointers)
>  - fsck isn't checking refcounts of reflinked extents yet
>  - bcachefs tests in ktest need to be moved to xfstests
>  - user docs are still very minimal
>
> So that's roughly where things are at. I think erasure coding is going 
> to to be
> bcachefs's killer feature (or at least one of them), and I'm pretty 
> excited
> about it: it's a completely new approach unlike ZFS and btrfs, no write 
> hole (we
> don't update existing stripes in place) and we don't have to fragment 
> writes
> either like ZFS does. Add to that the caching that we already do and 
> it's
> turning into a pretty amazing tool for managing a whole bunch of mixed 
> storage.

--
  Oleksandr Natalenko (post-factum)