On Thu, Jan 12, 2012 at 04:28:47PM -0800, Andi Kleen wrote: > Here's a slightly updated version of the BTRFS snappy interface. > snappy is a faster compression algorithm that provides similar > compression as LZO, but generally better performance. Recently the LZ4 method showed up on the real-time compression scene http://fastcompression.blogspot.com/p/lz4.html (homepage) http://code.google.com/p/lz4/ (source repo) it has comparable performance and compression ratio to snappy. Quoting from the source repo main page: Name Ratio C.speed D.speed LZ4 (r41) 2.08 319 1070 LZO 2.05 1x_1 2.07 318 466 Snappy 1.0.4 2.02 242 683 My own benchmarking confirms that lz4 is has a bit faster decompression, but what is a big difference from snappy is it's memory consumption for compression: * 32kb for unbounded chunksize * 16kb for chunksize < 64k (a tuned compression) No additional memory is needed for decompression in both snappy and lz4. With a minor tweak and chunksize < 4G the context size could be reduced to 16k as well. There is also LZ4HC, "high compression" mode, which maintains same binary format, but the compression ratio is better. http://code.google.com/p/lz4hc/ Usecase: There could be the fast version used transparently and the -hc version could be allowed for the 'fi defrag' command in order to recompress selected files. LZ4 is written in C and it's BSD, LZ4HC is L-GPL. There is some space for improvements in the code, but as it's good already as it stands now. david -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
