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authorZbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>2014-12-06 21:33:27 -0500
committerZbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>2015-10-10 23:05:21 -0400
commit4b5bc5396c090ee41c45cab9052372d296c4a2f4 (patch)
tree374d0ab4f6da6b6ccc2716c9291027c9ef1a3952 /src/journal/test-compress-benchmark.c
parent898d5660eba688c566e90d0a15050dfeb8b8265d (diff)
coredump: use lz4frame api to compress coredumps
This converts the stream compression to use the new lz4frame api, compatible with lz4cat. Previous code used custom headers, so the compressed file was not compatible with lz4 command line tools. I considered this the last blocker to using lz4 by default. Speed seems to be reasonable, although a bit (a few percent) slower than the lz4 binary, even though compression is the same. I don't consider this important. It could be caused by the overhead of library calls, but is probably caused by slightly different buffer sizes or such. The code in this patch uses mmap, since since this allows the buffer to be reused while not making the code more complicated at all. In my testing, this version is noticably faster (~20%) than a naive single-buffered version. mmap can cause the program to be killed with SIGBUS, if the underlying file is truncated or a disk error occurs. We only use this from within coredump and coredumpctl, so I don't consider this an issue. Old decompression code is retained and is used if the new code fails indicating a format error. There have been reports of various smaller distributions using previous lz4 code, i.e. the old format, and it is nice to provide backwards compatibility. We can remove the legacy code in a few versions. The way that blobs are compressed in the journal is not affected.
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