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To:     linux-crypto@vger.kernel.org
From:   Jean-Denis Girard <jd.girard@sysnux.pf>
Subject: Re: [GIT PULL][PATCH v11 0/4] Update to zstd-1.4.10
Date:   Fri, 11 Jun 2021 10:06:58 -1000
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Hi list,

Le 29/04/2021 à 15:31, Nick Terrell a écrit :
> From: Nick Terrell <terrelln@fb.com>
> 
> Please pull from
> 
>    git@github.com:terrelln/linux.git tags/v11-zstd-1.4.10
> 
> to get these changes. Alternatively the patchset is included.
> 
> This patchset lists me as the maintainer for zstd and 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 released zstd-1.4.10 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 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-1.4.6 maintains the same API
> and preserves the semantics, so that none of the callers need to be updated.
> 
> This patchset comes in 2 parts:
> 1. The first 2 patches prepare for the zstd upgrade. The first patch adds the
>     new kernel style API 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-1.4.10. This patch is completely generated from upstream using
>     automated tooling.
> 
> I tested every caller of zstd on x86_64. I tested both after the 1.4.10 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. For example the 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


I've been using this series on stable kernel since 5.12.3 (now on 
5.12.10) on my main system without issues.

Tested-by: Jean-Denis Girard <jd.girard@sysnux.pf>


Thanks,
-- 
Jean-Denis Girard

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