Re: [GIT PULL] zstd changes for v5.16

From: Sedat Dilek
Date: Sat Nov 13 2021 - 16:07:52 EST

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On Tue, Nov 9, 2021 at 2:24 AM Nick Terrell <nickrterrell@xxxxxxxxx> wrote:
>
> From: Nick Terrell <terrelln@xxxxxx>
>
> Hi Linus,
>
> I am sending you a pull request to add myself as the maintainer of zstd and
> update the zstd version in the kernel, which is now 4 years out of date,
> to the latest zstd release. This includes bug fixes, much more extensive fuzzing,
> and performance improvements. And generates the kernel zstd automatically
> from upstream zstd, so it is easier to keep the zstd verison up to date, and we
> don't fall so far out of date again.
>

Hi Nick,

is it possible to have an adapted version of your work for Linux
v5.15.y which is a new kernel with LongTerm Support (see [1])?

Thanks.

Regards,
- Sedat -

[1] https://www.kernel.org/category/releases.html

> Thanks,
> Nick Terrell
>
> The following changes since commit d2f38a3c6507b2520101f9a3807ed98f1bdc545a:
>
> Merge tag 'backlight-next-5.16' of git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight (2021-11-08 12:21:28 -0800)
>
> are available in the Git repository at:
>
> git@xxxxxxxxxx:terrelln/linux.git tags/zstd-for-linus-v5.16
>
> for you to fetch changes up to 0a8ea235837cc39f27c45689930aa97ae91d5953:
>
> lib: zstd: Add cast to silence clang's -Wbitwise-instead-of-logical (2021-11-08 16:55:38 -0800)
>
> ----------------------------------------------------------------
> Update to zstd-1.4.10
>
> This PR includes 5 commits that update the zstd library version:
>
> 1. 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.
> 2. 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.
> 3. Imports the zstd-1.4.10 source code. This commit is automatically generated
> from upstream zstd (https://github.com/facebook/zstd).
> 4. Adds me (terrelln@xxxxxx) as the maintainer of `lib/zstd`.
> 5. Fixes a newly added build warning for clang.
>
> 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.
>
> Where is the previous discussion?
> ---------------------------------
>
> Links for the discussions of the previous versions of the patch set.
> The largest changes in the design of the patchset are driven by the discussions
> in V11, V5, and V1. Sorry for the mix of links, I couldn't find most of the the
> threads on lkml.org.
>
> V12: https://www.spinics.net/lists/linux-crypto/msg58189.html
> V11: https://lore.kernel.org/linux-btrfs/20210430013157.747152-1-nickrterrell@xxxxxxxxx/
> V10: https://lore.kernel.org/lkml/20210426234621.870684-2-nickrterrell@xxxxxxxxx/
> V9: https://lore.kernel.org/linux-btrfs/20210330225112.496213-1-nickrterrell@xxxxxxxxx/
> V8: https://lore.kernel.org/linux-f2fs-devel/20210326191859.1542272-1-nickrterrell@xxxxxxxxx/
> V7: https://lkml.org/lkml/2020/12/3/1195
> V6: https://lkml.org/lkml/2020/12/2/1245
> V5: https://lore.kernel.org/linux-btrfs/20200916034307.2092020-1-nickrterrell@xxxxxxxxx/
> V4: https://www.spinics.net/lists/linux-btrfs/msg105783.html
> V3: https://lkml.org/lkml/2020/9/23/1074
> V2: https://www.spinics.net/lists/linux-btrfs/msg105505.html
> V1: https://lore.kernel.org/linux-btrfs/20200916034307.2092020-1-nickrterrell@xxxxxxxxx/
>
> Signed-off-by: Nick Terrell <terrelln@xxxxxx>
> Tested By: Paul Jones <paul@xxxxxxxxxxxxxxx>
> Tested-by: Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx>
> Tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> # LLVM/Clang v13.0.0 on x86-64
> Tested-by: Jean-Denis Girard <jd.girard@xxxxxxxxx>
>
> ----------------------------------------------------------------
> Nathan Chancellor (1):
> lib: zstd: Add cast to silence clang's -Wbitwise-instead-of-logical
>
> 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 | 1414 +++++++
> 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 | 1346 +++++++
> 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 | 2085 ++++++++++
> 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, 27373 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

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