102 lines
5.1 KiB
Markdown
102 lines
5.1 KiB
Markdown
# Linux Kernel Patch
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There are four pieces, the `xxhash` kernel module, the `zstd_compress` and `zstd_decompress` kernel modules, the BtrFS patch, and the SquashFS patch.
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The patches are based off of the linux kernel master branch.
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## xxHash kernel module
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* The patch is located in `xxhash.diff`.
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* The header is in `include/linux/xxhash.h`.
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* The source is in `lib/xxhash.c`.
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* `test/XXHashUserLandTest.cpp` contains tests for the patch in userland by mocking the kernel headers.
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I tested the tests by commenting a line of of each branch in `xxhash.c` one line at a time, and made sure the tests failed.
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It can be run with the following commands:
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```
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cd test && make googletest && make XXHashUserLandTest && ./XXHashUserLandTest
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```
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* I also benchmarked the `xxhash` module against upstream xxHash, and made sure that they ran at the same speed.
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## Zstd Kernel modules
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* The (large) patch is located in `zstd.diff`, which depends on `xxhash.diff`.
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* The header is in `include/linux/zstd.h`.
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* It is split up into `zstd_compress` and `zstd_decompress`, which can be loaded independently.
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* Source files are in `lib/zstd/`.
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* `lib/Kconfig` and `lib/Makefile` need to be modified by applying `lib/Kconfig.diff` and `lib/Makefile.diff` respectively.
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These changes are also included in the `zstd.diff`.
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* `test/UserlandTest.cpp` contains tests for the patch in userland by mocking the kernel headers.
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It can be run with the following commands:
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```
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cd test && make googletest && make UserlandTest && ./UserlandTest
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```
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## BtrFS
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* The patch is located in `btrfs.diff`.
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* Additionally `fs/btrfs/zstd.c` is provided as a source for convenience.
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* The patch seems to be working, it doesn't crash the kernel, and compresses at speeds and ratios that are expected.
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It could still use some more testing for fringe features, like printing options.
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### Benchmarks
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Benchmarks run on a Ubuntu 14.04 with 2 cores and 4 GiB of RAM.
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The VM is running on a Macbook Pro with a 3.1 GHz Intel Core i7 processor,
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16 GB of ram, and a SSD.
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The kernel running was built from the master branch with the patch.
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The compression benchmark is copying 10 copies of the
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unzipped [silesia corpus](http://mattmahoney.net/dc/silesia.html) into a BtrFS
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filesystem mounted with `-o compress-force={none, lzo, zlib, zstd}`.
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The decompression benchmark is timing how long it takes to `tar` all 10 copies
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into `/dev/null`.
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The compression ratio is measured by comparing the output of `df` and `du`.
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See `btrfs-benchmark.sh` for details.
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| Algorithm | Compression ratio | Compression speed | Decompression speed |
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|-----------|-------------------|-------------------|---------------------|
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| None | 0.99 | 504 MB/s | 686 MB/s |
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| lzo | 1.66 | 398 MB/s | 442 MB/s |
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| zlib | 2.58 | 65 MB/s | 241 MB/s |
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| zstd 1 | 2.57 | 260 MB/s | 383 MB/s |
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| zstd 3 | 2.71 | 174 MB/s | 408 MB/s |
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| zstd 6 | 2.87 | 70 MB/s | 398 MB/s |
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| zstd 9 | 2.92 | 43 MB/s | 406 MB/s |
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| zstd 12 | 2.93 | 21 MB/s | 408 MB/s |
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| zstd 15 | 3.01 | 11 MB/s | 354 MB/s |
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## SquashFS
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* The patch is located in `squashfs.diff`
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* Additionally `fs/squashfs/zstd_wrapper.c` is provided as a source for convenience.
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* The patch has been tested on the master branch of the kernel.
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### Benchmarks
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Benchmarks run on a Ubuntu 14.04 with 2 cores and 4 GiB of RAM.
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The VM is running on a Macbook Pro with a 3.1 GHz Intel Core i7 processor,
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16 GB of ram, and a SSD.
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The kernel running was built from the master branch with the patch.
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The compression benchmark is the file tree from the SquashFS archive found in the
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Ubuntu 16.10 desktop image (ubuntu-16.10-desktop-amd64.iso).
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The compression benchmark uses mksquashfs with the default block size (128 KB)
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and various compression algorithms/compression levels.
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`xz` and `zstd` are also benchmarked with 256 KB blocks.
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The decompression benchmark is timing how long it takes to `tar` the file tree
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into `/dev/null`.
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See `squashfs-benchmark.sh` for details.
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| Algorithm | Compression ratio | Compression speed | Decompression speed |
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|----------------|-------------------|-------------------|---------------------|
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| gzip | 2.92 | 15 MB/s | 128 MB/s |
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| lzo | 2.64 | 9.5 MB/s | 217 MB/s |
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| lz4 | 2.12 | 94 MB/s | 218 MB/s |
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| xz | 3.43 | 5.5 MB/s | 35 MB/s |
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| xz 256 KB | 3.53 | 5.4 MB/s | 40 MB/s |
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| zstd 1 | 2.71 | 96 MB/s | 210 MB/s |
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| zstd 5 | 2.93 | 69 MB/s | 198 MB/s |
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| zstd 10 | 3.01 | 41 MB/s | 225 MB/s |
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| zstd 15 | 3.13 | 11.4 MB/s | 224 MB/s |
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| zstd 16 256 KB | 3.24 | 8.1 MB/s | 210 MB/s |
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