Re: [GIT PULL] zstd changes for linux-next

[Sedat Dilek <sedat.dilek@gmail.com>]

On Wed, Oct 6, 2021 at 9:21 PM Nick Terrell <nickrterrell@gmail.com> wrote:
>
> From: Nick Terrell <terrelln@fb.com>
>
> The following changes since commit 9e1ff307c779ce1f0f810c7ecce3d95bbae40896:
>
>   Linux 5.15-rc4 (2021-10-03 14:08:47 -0700)
>
> are available in the Git repository at:
>
>   https://github.com/terrelln/linux.git zstd-1.4.10
>
> for you to fetch changes up to a0ccd980d5048053578f3b524e3cd3f5d980a9c5:
>
>   MAINTAINERS: Add maintainer entry for zstd (2021-10-04 20:04:32 -0700)
>
> I would like to merge this pull request into linux-next to bake, and then submit
> the PR to Linux in the 5.16 merge window. If you have been a part of the
> discussion, are a maintainer of a caller of zstd, tested this code, or otherwise
> been involved, thank you! And could you please respond below with an appropiate
> tag, so I can collect support for the PR
>
> Best,
> Nick Terrell
>
> ----------------------------------------------------------------
> Update to zstd-1.4.10
>
> - The first commit adds a new kernel-style wrapper around zstd. This wrapper API
>   is functionally equivalent to the subset of the current zstd API that is
>   currently used. The wrapper API changes to be kernel style so that the symbols
>   don't collide with zstd's symbols. The update to zstd-1.4.10 maintains the same
>   API and preserves the semantics, so that none of the callers need to be
>   updated. All callers are updated in the commit, because there are zero
>   functional changes.
> - The second commit adds an indirection for `lib/decompress_unzstd.c` so it
>   doesn't depend on the layout of `lib/zstd/` to include every source file.
>   This allows the next patch to be automatically generated.
> - The third commit is automatically generated, and imports the zstd-1.4.10 source
>   code. This commit is completely generated by automation.
> - The fourth commit adds me (terrelln@fb.com) as the maintainer of `lib/zstd`.
>
> The discussion around this patchset has been pretty long, so I've included a
> FAQ-style summary of the history of the patchset, and why we are taking this
> approach.
>
> Why do we need to update?
> -------------------------
>
> The zstd version in the kernel is based off of zstd-1.3.1, which is was released
> August 20, 2017. Since then zstd has seen many bug fixes and performance
> improvements. And, importantly, upstream zstd is continuously fuzzed by OSS-Fuzz,
> and bug fixes aren't backported to older versions. So the only way to sanely get
> these fixes is to keep up to date with upstream zstd. There are no known security
> issues that affect the kernel, but we need to be able to update in case there
> are. And while there are no known security issues, there are relevant bug fixes.
> For example the problem with large kernel decompression has been fixed upstream
> for over 2 years https://lkml.org/lkml/2020/9/29/27.
>
> Additionally the performance improvements for kernel use cases are significant.
> Measured for x86_64 on my Intel i9-9900k @ 3.6 GHz:
>
> - BtrFS zstd compression at levels 1 and 3 is 5% faster
> - BtrFS zstd decompression+read is 15% faster
> - SquashFS zstd decompression+read is 15% faster
> - F2FS zstd compression+write at level 3 is 8% faster
> - F2FS zstd decompression+read is 20% faster
> - ZRAM decompression+read is 30% faster
> - Kernel zstd decompression is 35% faster
> - Initramfs zstd decompression+build is 5% faster
>
> On top of this, there are significant performance improvements coming down the
> line in the next zstd release, and the new automated update patch generation
> will allow us to pull them easily.
>
> How is the update patch generated?
> ----------------------------------
>
> The first two patches are preparation for updating the zstd version. Then the
> 3rd patch in the series imports upstream zstd into the kernel. This patch is
> automatically generated from upstream. A script makes the necessary changes and
> imports it into the kernel. The changes are:
>
> - Replace all libc dependencies with kernel replacements and rewrite includes.
> - Remove unncessary portability macros like: #if defined(_MSC_VER).
> - Use the kernel xxhash instead of bundling it.
>
> This automation gets tested every commit by upstream's continuous integration.
> When we cut a new zstd release, we will submit a patch to the kernel to update
> the zstd version in the kernel.
>
> The automated process makes it easy to keep the kernel version of zstd up to
> date. The current zstd in the kernel shares the guts of the code, but has a lot
> of API and minor changes to work in the kernel. This is because at the time
> upstream zstd was not ready to be used in the kernel envrionment as-is. But,
> since then upstream zstd has evolved to support being used in the kernel as-is.
>
> Why are we updating in one big patch?
> -------------------------------------
>
> The 3rd patch in the series is very large. This is because it is restructuring
> the code, so it both deletes the existing zstd, and re-adds the new structure.
> Future updates will be directly proportional to the changes in upstream zstd
> since the last import. They will admittidly be large, as zstd is an actively
> developed project, and has hundreds of commits between every release. However,
> there is no other great alternative.
>
> One option ruled out is to replay every upstream zstd commit. This is not feasible
> for several reasons:
> - There are over 3500 upstream commits since the zstd version in the kernel.
> - The automation to automatically generate the kernel update was only added recently,
>   so older commits cannot easily be imported.
> - Not every upstream zstd commit builds.
> - Only zstd releases are "supported", and individual commits may have bugs that were
>   fixed before a release.
>
> Another option to reduce the patch size would be to first reorganize to the new
> file structure, and then apply the patch. However, the current kernel zstd is formatted
> with clang-format to be more "kernel-like". But, the new method imports zstd as-is,
> without additional formatting, to allow for closer correlation with upstream, and
> easier debugging. So the patch wouldn't be any smaller.
>
> It also doesn't make sense to import upstream zstd commit by commit going
> forward. Upstream zstd doesn't support production use cases running of the
> development branch. We have a lot of post-commit fuzzing that catches many bugs,
> so indiviudal commits may be buggy, but fixed before a release. So going forward,
> I intend to import every (important) zstd release into the Kernel.
>
> So, while it isn't ideal, updating in one big patch is the only patch I see forward.
>
> Who is responsible for this code?
> ---------------------------------
>
> I am. This patchset adds me as the maintainer for zstd. Previously, there was no tree
> for zstd patches. Because of that, there were several patches that either got ignored,
> or took a long time to merge, since it wasn't clear which tree should pick them up.
> I'm officially stepping up as maintainer, and setting up my tree as the path through
> which zstd patches get merged. I'll make sure that patches to the kernel zstd get
> ported upstream, so they aren't erased when the next version update happens.
>
> How is this code tested?
> ------------------------
>
> I tested every caller of zstd on x86_64 (BtrFS, ZRAM, SquashFS, F2FS, Kernel,
> InitRAMFS). I also tested Kernel & InitRAMFS on i386 and aarch64. I checked both
> performance and correctness.
>
> Also, thanks to many people in the community who have tested these patches locally.
> If you have tested the patches, please reply with a Tested-By so I can collect them
> for the PR I will send to Linus.
>
> Lastly, this code will bake in linux-next before being merged into v5.16.
>
> Why update to zstd-1.4.10 when zstd-1.5.0 has been released?
> ------------------------------------------------------------
>
> This patchset has been outstanding since 2020, and zstd-1.4.10 was the latest
> release when it was created. Since the update patch is automatically generated
> from upstream, I could generate it from zstd-1.5.0. However, there were some
> large stack usage regressions in zstd-1.5.0, and are only fixed in the latest
> development branch. And the latest development branch contains some new code that
> needs to bake in the fuzzer before I would feel comfortable releasing to the
> kernel.
>
> Once this patchset has been merged, and we've released zstd-1.5.1, we can update
> the kernel to zstd-1.5.1, and exercise the update process.
>
> You may notice that zstd-1.4.10 doesn't exist upstream. This release is an
> artifical release based off of zstd-1.4.9, with some fixes for the kernel
> backported from the development branch. I will tag the zstd-1.4.10 release after
> this patchset is merged, so the Linux Kernel is running a known version of zstd
> that can be debugged upstream.
>
> Why was a wrapper API added?
> ----------------------------
>
> The first versions of this patchset migrated the kernel to the upstream zstd
> API. It first added a shim API that supported the new upstream API with the old
> code, then updated callers to use the new shim API, then transitioned to the
> new code and deleted the shim API. However, Cristoph Hellwig suggested that we
> transition to a kernel style API, and hide zstd's upstream API behind that.
> This is because zstd's upstream API is supports many other use cases, and does
> not follow the kernel style guide, while the kernel API is focused on the
> kernel's use cases, and follows the kernel style guide.
>
> Changelog
> ---------
>
> v1 -> v2:
> * Successfully tested F2FS with help from Chao Yu to fix my test.
> * (1/9) Fix ZSTD_initCStream() wrapper to handle pledged_src_size=0 means unknown.
>   This fixes F2FS with the zstd-1.4.6 compatibility wrapper, exposed by the test.
>
> v2 -> v3:
> * (3/9) Silence warnings by Kernel Test Robot:
>   https://github.com/facebook/zstd/pull/2324
>   Stack size warnings remain, but these aren't new, and the functions it warns on
>   are either unused or not in the maximum stack path. This patchset reduces zstd
>   compression stack usage by 1 KB overall. I've gotten the low hanging fruit, and
>   more stack reduction would require significant changes that have the potential
>   to introduce new bugs. However, I do hope to continue to reduce zstd stack
>   usage in future versions.
>
> v3 -> v4:
> * (3/9) Fix errors and warnings reported by Kernel Test Robot:
>   https://github.com/facebook/zstd/pull/2326
>   - Replace mem.h with a custom kernel implementation that matches the current
>     lib/zstd/mem.h in the kernel. This avoids calls to __builtin_bswap*() which
>     don't work on certain architectures, as exposed by the Kernel Test Robot.
>   - Remove ASAN/MSAN (un)poisoning code which doesn't work in the kernel, as
>     exposed by the Kernel Test Robot.
>   - I've fixed all of the valid cppcheck warnings reported, but there were many
>     false positives, where cppcheck was incorrectly analyzing the situation,
>     which I did not fix. I don't believe it is reasonable to expect that upstream
>     zstd silences all the static analyzer false positives. Upstream zstd uses
>     clang scan-build for its static analysis. We find that supporting multiple
>     static analysis tools multiplies the burden of silencing false positives,
>     without providing enough marginal value over running a single static analysis
>     tool.
>
> v4 -> v5:
> * Rebase onto v5.10-rc2
> * (6/9) Merge with other F2FS changes (no functional change in patch).
>
> v5 -> v6:
> * Rebase onto v5.10-rc6.
> * Switch to using a kernel style wrapper API as suggested by Cristoph.
>
> v6 -> v7:
> * Expose the upstream library header as `include/linux/zstd_lib.h`.
>   Instead of creating new structs mirroring the upstream zstd structs
>   use upstream's structs directly with a typedef to get a kernel style name.
>   This removes the memcpy cruft.
> * (1/3) Undo ZSTD_WINDOWLOG_MAX and handle_zstd_error changes.
> * (3/3) Expose zstd_errors.h as `include/linux/zstd_errors.h` because it
>   is needed by the kernel wrapper API.
>
> v7 -> v8:
> * (1/3) Fix typo in EXPORT_SYMBOL().
> * (1/3) Fix typo in zstd.h comments.
> * (3/3) Update to latest zstd release: 1.4.6 -> 1.4.10
>         This includes ~1KB of stack space reductions.
>
> v8 -> v9:
> * (1/3) Rebase onto v5.12-rc5
> * (1/3) Add zstd_min_clevel() & zstd_max_clevel() and use in f2fs.
>         Thanks to Oleksandr Natalenko for spotting it!
> * (1/3) Move lib/decompress_unzstd.c usage of ZSTD_getErrorCode()
>         to zstd_get_error_code().
> * (1/3) Update modified zstd headers to yearless copyright.
> * (2/3) Add copyright/license header to decompress_sources.h for consistency.
> * (3/3) Update to yearless copyright for all zstd files. Thanks to
>         Mike Dolan for spotting it!
>
> v9 -> v10:
> * Add a 4th patch in the series which adds an entry for zstd to MAINTAINERS.
>
> v10 -> v11:
> * Rebase cleanly onto v5.12-rc8
> * (3/4) Replace invalid kernel style comments in zstd with regular comments.
>         Thanks to Randy Dunlap for the suggestion.
>
> v11 -> v12:
> * Re-write the cover letter & send as a PR only.
> * Rebase cleanly onto 5.15-rc4.
> * (3/4) Clean up licensing to reflect that we're GPL-2.0+ OR BSD-3-Clause.
> * (3/4) Reduce compression stack usage by 80 bytes.
> * (3/4) Make upstream zstd `-Wfall-through` compliant and use the FALLTHROUGH
>         macro in the Linux Kernel.
>
> Signed-off-by: Nick Terrell <terrelln@fb.com>
> Tested By: Paul Jones <paul@pauljones.id.au>
> Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
>

Hi Nick,

can you please CC me on further patchsets?

Thanks for taking responsibility as linux-zstd maintainer.

I am currently testing this on top of Linux v5.15-rc4 building with
LLVM/Clang v13.

Do I also need ZSTD version 1.4.10 in user-space?
Debian/unstable AMD64 ships here version 1.4.8.

Thanks.

Regards,
- Sedat -

> ----------------------------------------------------------------
> Nick Terrell (4):
>       lib: zstd: Add kernel-specific API
>       lib: zstd: Add decompress_sources.h for decompress_unzstd
>       lib: zstd: Upgrade to latest upstream zstd version 1.4.10
>       MAINTAINERS: Add maintainer entry for zstd
>
>  MAINTAINERS                                    |   12 +
>  crypto/zstd.c                                  |   28 +-
>  fs/btrfs/zstd.c                                |   68 +-
>  fs/f2fs/compress.c                             |   56 +-
>  fs/f2fs/super.c                                |    2 +-
>  fs/pstore/platform.c                           |    2 +-
>  fs/squashfs/zstd_wrapper.c                     |   16 +-
>  include/linux/zstd.h                           | 1252 ++----
>  include/linux/zstd_errors.h                    |   77 +
>  include/linux/zstd_lib.h                       | 2432 +++++++++++
>  lib/decompress_unzstd.c                        |   48 +-
>  lib/zstd/Makefile                              |   46 +-
>  lib/zstd/bitstream.h                           |  380 --
>  lib/zstd/common/bitstream.h                    |  437 ++
>  lib/zstd/common/compiler.h                     |  170 +
>  lib/zstd/common/cpu.h                          |  194 +
>  lib/zstd/common/debug.c                        |   24 +
>  lib/zstd/common/debug.h                        |  101 +
>  lib/zstd/common/entropy_common.c               |  357 ++
>  lib/zstd/common/error_private.c                |   56 +
>  lib/zstd/common/error_private.h                |   66 +
>  lib/zstd/common/fse.h                          |  710 ++++
>  lib/zstd/common/fse_decompress.c               |  390 ++
>  lib/zstd/common/huf.h                          |  356 ++
>  lib/zstd/common/mem.h                          |  259 ++
>  lib/zstd/common/zstd_common.c                  |   83 +
>  lib/zstd/common/zstd_deps.h                    |  125 +
>  lib/zstd/common/zstd_internal.h                |  450 +++
>  lib/zstd/compress.c                            | 3485 ----------------
>  lib/zstd/compress/fse_compress.c               |  625 +++
>  lib/zstd/compress/hist.c                       |  165 +
>  lib/zstd/compress/hist.h                       |   75 +
>  lib/zstd/compress/huf_compress.c               |  905 +++++
>  lib/zstd/compress/zstd_compress.c              | 5109 ++++++++++++++++++++++++
>  lib/zstd/compress/zstd_compress_internal.h     | 1188 ++++++
>  lib/zstd/compress/zstd_compress_literals.c     |  158 +
>  lib/zstd/compress/zstd_compress_literals.h     |   29 +
>  lib/zstd/compress/zstd_compress_sequences.c    |  439 ++
>  lib/zstd/compress/zstd_compress_sequences.h    |   54 +
>  lib/zstd/compress/zstd_compress_superblock.c   |  850 ++++
>  lib/zstd/compress/zstd_compress_superblock.h   |   32 +
>  lib/zstd/compress/zstd_cwksp.h                 |  482 +++
>  lib/zstd/compress/zstd_double_fast.c           |  519 +++
>  lib/zstd/compress/zstd_double_fast.h           |   32 +
>  lib/zstd/compress/zstd_fast.c                  |  496 +++
>  lib/zstd/compress/zstd_fast.h                  |   31 +
>  lib/zstd/compress/zstd_lazy.c                  | 1412 +++++++
>  lib/zstd/compress/zstd_lazy.h                  |   81 +
>  lib/zstd/compress/zstd_ldm.c                   |  686 ++++
>  lib/zstd/compress/zstd_ldm.h                   |  110 +
>  lib/zstd/compress/zstd_ldm_geartab.h           |  103 +
>  lib/zstd/compress/zstd_opt.c                   | 1345 +++++++
>  lib/zstd/compress/zstd_opt.h                   |   50 +
>  lib/zstd/decompress.c                          | 2531 ------------
>  lib/zstd/decompress/huf_decompress.c           | 1206 ++++++
>  lib/zstd/decompress/zstd_ddict.c               |  241 ++
>  lib/zstd/decompress/zstd_ddict.h               |   44 +
>  lib/zstd/decompress/zstd_decompress.c          | 2082 ++++++++++
>  lib/zstd/decompress/zstd_decompress_block.c    | 1540 +++++++
>  lib/zstd/decompress/zstd_decompress_block.h    |   62 +
>  lib/zstd/decompress/zstd_decompress_internal.h |  202 +
>  lib/zstd/decompress_sources.h                  |   28 +
>  lib/zstd/entropy_common.c                      |  243 --
>  lib/zstd/error_private.h                       |   53 -
>  lib/zstd/fse.h                                 |  575 ---
>  lib/zstd/fse_compress.c                        |  795 ----
>  lib/zstd/fse_decompress.c                      |  325 --
>  lib/zstd/huf.h                                 |  212 -
>  lib/zstd/huf_compress.c                        |  773 ----
>  lib/zstd/huf_decompress.c                      |  960 -----
>  lib/zstd/mem.h                                 |  151 -
>  lib/zstd/zstd_common.c                         |   75 -
>  lib/zstd/zstd_compress_module.c                |  160 +
>  lib/zstd/zstd_decompress_module.c              |  105 +
>  lib/zstd/zstd_internal.h                       |  273 --
>  lib/zstd/zstd_opt.h                            | 1014 -----
>  76 files changed, 27367 insertions(+), 12941 deletions(-)
>  create mode 100644 include/linux/zstd_errors.h
>  create mode 100644 include/linux/zstd_lib.h
>  delete mode 100644 lib/zstd/bitstream.h
>  create mode 100644 lib/zstd/common/bitstream.h
>  create mode 100644 lib/zstd/common/compiler.h
>  create mode 100644 lib/zstd/common/cpu.h
>  create mode 100644 lib/zstd/common/debug.c
>  create mode 100644 lib/zstd/common/debug.h
>  create mode 100644 lib/zstd/common/entropy_common.c
>  create mode 100644 lib/zstd/common/error_private.c
>  create mode 100644 lib/zstd/common/error_private.h
>  create mode 100644 lib/zstd/common/fse.h
>  create mode 100644 lib/zstd/common/fse_decompress.c
>  create mode 100644 lib/zstd/common/huf.h
>  create mode 100644 lib/zstd/common/mem.h
>  create mode 100644 lib/zstd/common/zstd_common.c
>  create mode 100644 lib/zstd/common/zstd_deps.h
>  create mode 100644 lib/zstd/common/zstd_internal.h
>  delete mode 100644 lib/zstd/compress.c
>  create mode 100644 lib/zstd/compress/fse_compress.c
>  create mode 100644 lib/zstd/compress/hist.c
>  create mode 100644 lib/zstd/compress/hist.h
>  create mode 100644 lib/zstd/compress/huf_compress.c
>  create mode 100644 lib/zstd/compress/zstd_compress.c
>  create mode 100644 lib/zstd/compress/zstd_compress_internal.h
>  create mode 100644 lib/zstd/compress/zstd_compress_literals.c
>  create mode 100644 lib/zstd/compress/zstd_compress_literals.h
>  create mode 100644 lib/zstd/compress/zstd_compress_sequences.c
>  create mode 100644 lib/zstd/compress/zstd_compress_sequences.h
>  create mode 100644 lib/zstd/compress/zstd_compress_superblock.c
>  create mode 100644 lib/zstd/compress/zstd_compress_superblock.h
>  create mode 100644 lib/zstd/compress/zstd_cwksp.h
>  create mode 100644 lib/zstd/compress/zstd_double_fast.c
>  create mode 100644 lib/zstd/compress/zstd_double_fast.h
>  create mode 100644 lib/zstd/compress/zstd_fast.c
>  create mode 100644 lib/zstd/compress/zstd_fast.h
>  create mode 100644 lib/zstd/compress/zstd_lazy.c
>  create mode 100644 lib/zstd/compress/zstd_lazy.h
>  create mode 100644 lib/zstd/compress/zstd_ldm.c
>  create mode 100644 lib/zstd/compress/zstd_ldm.h
>  create mode 100644 lib/zstd/compress/zstd_ldm_geartab.h
>  create mode 100644 lib/zstd/compress/zstd_opt.c
>  create mode 100644 lib/zstd/compress/zstd_opt.h
>  delete mode 100644 lib/zstd/decompress.c
>  create mode 100644 lib/zstd/decompress/huf_decompress.c
>  create mode 100644 lib/zstd/decompress/zstd_ddict.c
>  create mode 100644 lib/zstd/decompress/zstd_ddict.h
>  create mode 100644 lib/zstd/decompress/zstd_decompress.c
>  create mode 100644 lib/zstd/decompress/zstd_decompress_block.c
>  create mode 100644 lib/zstd/decompress/zstd_decompress_block.h
>  create mode 100644 lib/zstd/decompress/zstd_decompress_internal.h
>  create mode 100644 lib/zstd/decompress_sources.h
>  delete mode 100644 lib/zstd/entropy_common.c
>  delete mode 100644 lib/zstd/error_private.h
>  delete mode 100644 lib/zstd/fse.h
>  delete mode 100644 lib/zstd/fse_compress.c
>  delete mode 100644 lib/zstd/fse_decompress.c
>  delete mode 100644 lib/zstd/huf.h
>  delete mode 100644 lib/zstd/huf_compress.c
>  delete mode 100644 lib/zstd/huf_decompress.c
>  delete mode 100644 lib/zstd/mem.h
>  delete mode 100644 lib/zstd/zstd_common.c
>  create mode 100644 lib/zstd/zstd_compress_module.c
>  create mode 100644 lib/zstd/zstd_decompress_module.c
>  delete mode 100644 lib/zstd/zstd_internal.h
>  delete mode 100644 lib/zstd/zstd_opt.h