• Nick Terrell's avatar
    lib: zstd: Upgrade to latest upstream zstd version 1.4.10 · e0c1b49f
    Nick Terrell authored
    Upgrade to the latest upstream zstd version 1.4.10.
    
    This patch is 100% generated from upstream zstd commit 20821a46f412 [0].
    
    This patch is very large because it is transitioning from the custom
    kernel zstd to using upstream directly. The new zstd follows upstreams
    file structure which is different. Future update patches will be much
    smaller because they will only contain the changes from one upstream
    zstd release.
    
    As an aid for review I've created a commit [1] that shows the diff
    between upstream zstd as-is (which doesn't compile), and the zstd
    code imported in this patch. The verion of zstd in this patch is
    generated from upstream with changes applied by automation to replace
    upstreams libc dependencies, remove unnecessary portability macros,
    replace `/**` comments with `/*` comments, and use the kernel's xxhash
    instead of bundling it.
    
    The benefits of this patch are as follows:
    1. Using upstream directly with automated script to generate kernel
       code. This allows us to update the kernel every upstream release, so
       the kernel gets the latest bug fixes and performance improvements,
       and doesn't get 3 years out of date again. The automation and the
       translated code are tested every upstream commit to ensure it
       continues to work.
    2. Upgrades from a custom zstd based on 1.3.1 to 1.4.10, getting 3 years
       of performance improvements and bug fixes. On x86_64 I've measured
       15% faster BtrFS and SquashFS decompression+read speeds, 35% faster
       kernel decompression, and 30% faster ZRAM decompression+read speeds.
    3. Zstd-1.4.10 supports negative compression levels, which allow zstd to
       match or subsume lzo's performance.
    4. Maintains the same kernel-specific wrapper API, so no callers have to
       be modified with zstd version updates.
    
    One concern that was brought up was stack usage. Upstream zstd had
    already removed most of its heavy stack usage functions, but I just
    removed the last functions that allocate arrays on the stack. I've
    measured the high water mark for both compression and decompression
    before and after this patch. Decompression is approximately neutral,
    using about 1.2KB of stack space. Compression levels up to 3 regressed
    from 1.4KB -> 1.6KB, and higher compression levels regressed from 1.5KB
    -> 2KB. We've added unit tests upstream to prevent further regression.
    I believe that this is a reasonable increase, and if it does end up
    causing problems, this commit can be cleanly reverted, because it only
    touches zstd.
    
    I chose the bulk update instead of replaying upstream commits because
    there have been ~3500 upstream commits since the 1.3.1 release, zstd
    wasn't ready to be used in the kernel as-is before a month ago, and not
    all upstream zstd commits build. 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.
    
    Note that upstream zstd release 1.4.10 doesn't exist yet. I have cut a
    staging branch at 20821a46f412 [0] and will apply any changes requested
    to the staging branch. Once we're ready to merge this update I will cut
    a zstd release at the commit we merge, so we have a known zstd release
    in the kernel.
    
    The implementation of the kernel API is contained in
    zstd_compress_module.c and zstd_decompress_module.c.
    
    [0] https://github.com/facebook/zstd/commit/20821a46f4122f9abd7c7b245d28162dde8129c9
    [1] https://github.com/terrelln/linux/commit/e0fa481d0e3df26918da0a13749740a1f6777574Signed-off-by: default avatarNick Terrell <terrelln@fb.com>
    Tested By: Paul Jones <paul@pauljones.id.au>
    Tested-by: default avatarOleksandr Natalenko <oleksandr@natalenko.name>
    Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM/Clang v13.0.0 on x86-64
    Tested-by: default avatarJean-Denis Girard <jd.girard@sysnux.pf>
    e0c1b49f
debug.h 3.58 KB