Re: [PATCH v4 0/9] Update to zstd-1.4.6

[Nick Terrell <terrelln@fb.com>]

> On Sep 29, 2020, at 11:53 PM, Christoph Hellwig <hch@infradead.org> wrote:
> 
> As you keep resend this I keep retelling you that should not do it.
> Please provide a proper Linux API, and switch to that.  Versioned APIs
> have absolutely no business in the Linux kernel.

The API is not versioned. We provide a stable ABI for a large section of our API,
and the parts that aren’t ABI stable don’t change in semantics, and undergo long
deprecation periods before being removed.

The change of callers is a one-time change to transition from the existing API
in the kernel, which was never upstream's API, to upstream's API.

-Nick

> On Tue, Sep 29, 2020 at 11:53:09PM -0700, Nick Terrell wrote:
>> From: Nick Terrell <terrelln@fb.com>
>> 
>> This patchset upgrades the zstd library to the latest upstream release. The
>> current zstd version in the kernel is a modified version of upstream zstd-1.3.1.
>> At the time it was integrated, zstd wasn't ready to be used in the kernel as-is.
>> But, it is now possible to use upstream zstd directly in the kernel.
>> 
>> I have not yet release zstd-1.4.6 upstream. I want the zstd version in the kernel
>> to match up with a known upstream release, so we know exactly what code is
>> running. Whenever this patchset is ready for merge, I will cut a release at the
>> upstream commit that gets merged. This should not be necessary for future
>> releases.
>> 
>> The kernel zstd library is automatically generated from upstream zstd. A script
>> makes the necessary changes and imports it into the kernel. The changes are:
>> 
>> 1. Replace all libc dependencies with kernel replacements and rewrite includes.
>> 2. Remove unncessary portability macros like: #if defined(_MSC_VER).
>> 3. 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.
>> 
>> I've updated zstd to upstream with one big patch because every commit must build,
>> so that precludes partial updates. Since the commit is 100% generated, I hope the
>> review burden is lightened. I considered replaying upstream commits, but that is
>> not possible because there have been ~3500 upstream commits since the last zstd
>> import, and the commits don't all build individually. The bulk update preserves
>> bisectablity because bugs can be bisected to the zstd version update. At that
>> point the update can be reverted, and we can work with upstream to find and fix
>> the bug. After this big switch in how the kernel consumes zstd, future patches
>> will be smaller, because they will only have one upstream release worth of
>> changes each.
>> 
>> This patchset changes the zstd API from a custom kernel API to the upstream API.
>> I considered wrapping the upstream API with a wrapper that is closer to the
>> kernel style guide. Following advise from https://lkml.org/lkml/2020/9/17/814
>> I've chosen to use the upstream API directly, to minimize opportunities to
>> introduce bugs, and because using the upstream API directly makes debugging and
>> communication with upstream easier.
>> 
>> This patchset comes in 3 parts:
>> 1. The first 2 patches prepare for the zstd upgrade. The first patch adds a
>>   compatibility wrapper so zstd can be upgraded without modifying any callers.
>>   The second patch adds an indirection for the lib/decompress_unzstd.c including
>>   of all decompression source files.
>> 2. Import zstd-1.4.6. This patch is completely generated from upstream using
>>   automated tooling.
>> 3. Update all callers to the zstd-1.4.6 API then delete the compatibility
>>   wrapper.
>> 
>> I tested every caller of zstd on x86_64. I tested both after the 1.4.6 upgrade
>> using the compatibility wrapper, and after the final patch in this series. 
>> 
>> I tested kernel and initramfs decompression in i386 and arm.
>> 
>> I ran benchmarks to compare the current zstd in the kernel with zstd-1.4.6.
>> I benchmarked on x86_64 using QEMU with KVM enabled on an Intel i9-9900k.
>> I found:
>> * 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
>> 
>> The latest zstd also offers bug fixes and a 1 KB reduction in stack uage during
>> compression. For example the recent problem with large kernel decompression has
>> been fixed upstream for over 2 years https://lkml.org/lkml/2020/9/29/27.
>> 
>> Please let me know if there is anything that I can do to ease the way for these
>> patches. I think it is important because it gets large performance improvements,
>> contains bug fixes, and is switching to a more maintainable model of consuming
>> upstream zstd directly, making it easy to keep up to date.
>> 
>> Best,
>> Nick Terrell
>> 
>> 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.
>> 
>> Nick Terrell (9):
>>  lib: zstd: Add zstd compatibility wrapper
>>  lib: zstd: Add decompress_sources.h for decompress_unzstd
>>  lib: zstd: Upgrade to latest upstream zstd version 1.4.6
>>  crypto: zstd: Switch to zstd-1.4.6 API
>>  btrfs: zstd: Switch to the zstd-1.4.6 API
>>  f2fs: zstd: Switch to the zstd-1.4.6 API
>>  squashfs: zstd: Switch to the zstd-1.4.6 API
>>  lib: unzstd: Switch to the zstd-1.4.6 API
>>  lib: zstd: Remove zstd compatibility wrapper
>> 
>> crypto/zstd.c                                 |   22 +-
>> fs/btrfs/zstd.c                               |   46 +-
>> fs/f2fs/compress.c                            |  100 +-
>> fs/squashfs/zstd_wrapper.c                    |    7 +-
>> include/linux/zstd.h                          | 3021 ++++++++----
>> include/linux/zstd_errors.h                   |   76 +
>> lib/decompress_unzstd.c                       |   44 +-
>> lib/zstd/Makefile                             |   35 +-
>> lib/zstd/bitstream.h                          |  379 --
>> lib/zstd/common/bitstream.h                   |  437 ++
>> lib/zstd/common/compiler.h                    |  150 +
>> lib/zstd/common/cpu.h                         |  194 +
>> lib/zstd/common/debug.c                       |   24 +
>> lib/zstd/common/debug.h                       |  101 +
>> lib/zstd/common/entropy_common.c              |  355 ++
>> lib/zstd/common/error_private.c               |   55 +
>> lib/zstd/common/error_private.h               |   66 +
>> lib/zstd/common/fse.h                         |  709 +++
>> lib/zstd/common/fse_decompress.c              |  380 ++
>> lib/zstd/common/huf.h                         |  352 ++
>> lib/zstd/common/mem.h                         |  258 +
>> lib/zstd/common/zstd_common.c                 |   83 +
>> lib/zstd/common/zstd_deps.h                   |  124 +
>> lib/zstd/common/zstd_internal.h               |  438 ++
>> 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              |  764 +++
>> lib/zstd/compress/zstd_compress.c             | 4157 +++++++++++++++++
>> lib/zstd/compress/zstd_compress_internal.h    | 1103 +++++
>> lib/zstd/compress/zstd_compress_literals.c    |  158 +
>> lib/zstd/compress/zstd_compress_literals.h    |   29 +
>> lib/zstd/compress/zstd_compress_sequences.c   |  433 ++
>> lib/zstd/compress/zstd_compress_sequences.h   |   54 +
>> lib/zstd/compress/zstd_compress_superblock.c  |  849 ++++
>> lib/zstd/compress/zstd_compress_superblock.h  |   32 +
>> lib/zstd/compress/zstd_cwksp.h                |  465 ++
>> lib/zstd/compress/zstd_double_fast.c          |  521 +++
>> 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                 | 1138 +++++
>> lib/zstd/compress/zstd_lazy.h                 |   61 +
>> lib/zstd/compress/zstd_ldm.c                  |  619 +++
>> lib/zstd/compress/zstd_ldm.h                  |  104 +
>> lib/zstd/compress/zstd_opt.c                  | 1200 +++++
>> lib/zstd/compress/zstd_opt.h                  |   50 +
>> lib/zstd/decompress.c                         | 2531 ----------
>> lib/zstd/decompress/huf_decompress.c          | 1205 +++++
>> lib/zstd/decompress/zstd_ddict.c              |  241 +
>> lib/zstd/decompress/zstd_ddict.h              |   44 +
>> lib/zstd/decompress/zstd_decompress.c         | 1836 ++++++++
>> lib/zstd/decompress/zstd_decompress_block.c   | 1540 ++++++
>> lib/zstd/decompress/zstd_decompress_block.h   |   62 +
>> .../decompress/zstd_decompress_internal.h     |  195 +
>> lib/zstd/decompress_sources.h                 |   18 +
>> 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                       |  772 ---
>> lib/zstd/huf_decompress.c                     |  960 ----
>> lib/zstd/mem.h                                |  151 -
>> lib/zstd/zstd_common.c                        |   75 -
>> lib/zstd/zstd_compress_module.c               |   79 +
>> lib/zstd/zstd_decompress_module.c             |   79 +
>> lib/zstd/zstd_internal.h                      |  273 --
>> lib/zstd/zstd_opt.h                           | 1014 ----
>> 71 files changed, 24368 insertions(+), 13012 deletions(-)
>> create mode 100644 include/linux/zstd_errors.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_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
>> 
>> -- 
>> 2.28.0
>> 
> ---end quoted text---