2017-04-05 01:39:22 +00:00
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# Linux Kernel Patch
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There are two pieces, the `zstd_compress` and `zstd_decompress` kernel modules, and the BtrFS patch.
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2017-04-11 18:35:36 +00:00
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The patches are based off of the linux kernel master branch (version 4.10).
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2017-04-05 01:39:22 +00:00
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## Zstd Kernel modules
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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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* `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
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make googletest
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make UserlandTest
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./UserlandTest
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```
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## BtrFS
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2017-04-11 18:35:36 +00:00
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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 athat are expected.
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It can still use some more testing for fringe features, like printing options.
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2017-04-11 19:40:53 +00:00
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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 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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