• Nick Terrell's avatar
    lib: Add zstd modules · 73f3d1b4
    Nick Terrell authored
    Add zstd compression and decompression kernel modules.
    zstd offers a wide varity of compression speed and quality trade-offs.
    It can compress at speeds approaching lz4, and quality approaching lzma.
    zstd decompressions at speeds more than twice as fast as zlib, and
    decompression speed remains roughly the same across all compression levels.
    
    The code was ported from the upstream zstd source repository. The
    `linux/zstd.h` header was modified to match linux kernel style.
    The cross-platform and allocation code was stripped out. Instead zstd
    requires the caller to pass a preallocated workspace. The source files
    were clang-formatted [1] to match the Linux Kernel style as much as
    possible. Otherwise, the code was unmodified. We would like to avoid
    as much further manual modification to the source code as possible, so it
    will be easier to keep the kernel zstd up to date.
    
    I benchmarked zstd compression as a special character device. I ran zstd
    and zlib compression at several levels, as well as performing no
    compression, which measure the time spent copying the data to kernel space.
    Data is passed to the compresser 4096 B at a time. The benchmark file is
    located in the upstream zstd source repository under
    `contrib/linux-kernel/zstd_compress_test.c` [2].
    
    I ran the benchmarks on a Ubuntu 14.04 VM with 2 cores and 4 GiB of RAM.
    The VM is running on a MacBook Pro with a 3.1 GHz Intel Core i7 processor,
    16 GB of RAM, and a SSD. I benchmarked using `silesia.tar` [3], which is
    211,988,480 B large. Run the following commands for the benchmark:
    
        sudo modprobe zstd_compress_test
        sudo mknod zstd_compress_test c 245 0
        sudo cp silesia.tar zstd_compress_test
    
    The time is reported by the time of the userland `cp`.
    The MB/s is computed with
    
        1,536,217,008 B / time(buffer size, hash)
    
    which includes the time to copy from userland.
    The Adjusted MB/s is computed with
    
        1,536,217,088 B / (time(buffer size, hash) - time(buffer size, none)).
    
    The memory reported is the amount of memory the compressor requests.
    
    | Method   | Size (B) | Time (s) | Ratio | MB/s    | Adj MB/s | Mem (MB) |
    |----------|----------|----------|-------|---------|----------|----------|
    | none     | 11988480 |    0.100 |     1 | 2119.88 |        - |        - |
    | zstd -1  | 73645762 |    1.044 | 2.878 |  203.05 |   224.56 |     1.23 |
    | zstd -3  | 66988878 |    1.761 | 3.165 |  120.38 |   127.63 |     2.47 |
    | zstd -5  | 65001259 |    2.563 | 3.261 |   82.71 |    86.07 |     2.86 |
    | zstd -10 | 60165346 |   13.242 | 3.523 |   16.01 |    16.13 |    13.22 |
    | zstd -15 | 58009756 |   47.601 | 3.654 |    4.45 |     4.46 |    21.61 |
    | zstd -19 | 54014593 |  102.835 | 3.925 |    2.06 |     2.06 |    60.15 |
    | zlib -1  | 77260026 |    2.895 | 2.744 |   73.23 |    75.85 |     0.27 |
    | zlib -3  | 72972206 |    4.116 | 2.905 |   51.50 |    52.79 |     0.27 |
    | zlib -6  | 68190360 |    9.633 | 3.109 |   22.01 |    22.24 |     0.27 |
    | zlib -9  | 67613382 |   22.554 | 3.135 |    9.40 |     9.44 |     0.27 |
    
    I benchmarked zstd decompression using the same method on the same machine.
    The benchmark file is located in the upstream zstd repo under
    `contrib/linux-kernel/zstd_decompress_test.c` [4]. The memory reported is
    the amount of memory required to decompress data compressed with the given
    compression level. If you know the maximum size of your input, you can
    reduce the memory usage of decompression irrespective of the compression
    level.
    
    | Method   | Time (s) | MB/s    | Adjusted MB/s | Memory (MB) |
    |----------|----------|---------|---------------|-------------|
    | none     |    0.025 | 8479.54 |             - |           - |
    | zstd -1  |    0.358 |  592.15 |        636.60 |        0.84 |
    | zstd -3  |    0.396 |  535.32 |        571.40 |        1.46 |
    | zstd -5  |    0.396 |  535.32 |        571.40 |        1.46 |
    | zstd -10 |    0.374 |  566.81 |        607.42 |        2.51 |
    | zstd -15 |    0.379 |  559.34 |        598.84 |        4.61 |
    | zstd -19 |    0.412 |  514.54 |        547.77 |        8.80 |
    | zlib -1  |    0.940 |  225.52 |        231.68 |        0.04 |
    | zlib -3  |    0.883 |  240.08 |        247.07 |        0.04 |
    | zlib -6  |    0.844 |  251.17 |        258.84 |        0.04 |
    | zlib -9  |    0.837 |  253.27 |        287.64 |        0.04 |
    
    Tested in userland using the test-suite in the zstd repo under
    `contrib/linux-kernel/test/UserlandTest.cpp` [5] by mocking the kernel
    functions. Fuzz tested using libfuzzer [6] with the fuzz harnesses under
    `contrib/linux-kernel/test/{RoundTripCrash.c,DecompressCrash.c}` [7] [8]
    with ASAN, UBSAN, and MSAN. Additionaly, it was tested while testing the
    BtrFS and SquashFS patches coming next.
    
    [1] https://clang.llvm.org/docs/ClangFormat.html
    [2] https://github.com/facebook/zstd/blob/dev/contrib/linux-kernel/zstd_compress_test.c
    [3] http://sun.aei.polsl.pl/~sdeor/index.php?page=silesia
    [4] https://github.com/facebook/zstd/blob/dev/contrib/linux-kernel/zstd_decompress_test.c
    [5] https://github.com/facebook/zstd/blob/dev/contrib/linux-kernel/test/UserlandTest.cpp
    [6] http://llvm.org/docs/LibFuzzer.html
    [7] https://github.com/facebook/zstd/blob/dev/contrib/linux-kernel/test/RoundTripCrash.c
    [8] https://github.com/facebook/zstd/blob/dev/contrib/linux-kernel/test/DecompressCrash.c
    
    zstd source repository: https://github.com/facebook/zstdSigned-off-by: 's avatarNick Terrell <terrelln@fb.com>
    Signed-off-by: 's avatarChris Mason <clm@fb.com>
    73f3d1b4
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entropy_common.c Loading commit data...
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fse.h Loading commit data...
fse_compress.c Loading commit data...
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huf.h Loading commit data...
huf_compress.c Loading commit data...
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