Re: [RFC PATCH v2 2/4] lib: Add support for LZ4-compressed kernel
From: Kyungsik Lee
Date: Thu Feb 28 2013 - 00:23:00 EST
On Tue, Feb 26, 2013 at 03:00:51PM +0100, David Sterba wrote:
> On Tue, Feb 26, 2013 at 03:24:28PM +0900, Kyungsik Lee wrote:
> > +config KERNEL_LZ4
> > + bool "LZ4"
> > + depends on HAVE_KERNEL_LZ4
> > + help
> > + Its compression ratio is worse than LZO. The size of the kernel
> > + is about 8% bigger than LZO. But the decompression speed is
> > + faster than LZO.
> > +
> Can you please add a sentence what lz4 actually is before you start
> comparing it with the current competitor(s)?
Yes, I will update it.
> > --- /dev/null
> > +++ b/lib/decompress_unlz4.c
> > @@ -0,0 +1,190 @@
> > +#define LZ4_CHUNK_SIZE (8<<20)
> Please use a less cryptic way of representing a value of 8 MB. Also,
> this is a hardcoded value that must be used on the compressor side. It's
> an upper limit, so anything below 8MB does not break decompresssion, but
> this must be somehow checked or saved along in the binary stream. You
> seem to use the lz4demo.c on the userspace side for compression, but
> this is not a standard tool nor the output format is well-defined or
Yes, It will be easy to parse and extract the meta information required
for the kernel decompressor if output format is well-defined and
> For proper use I would like to see a commandline tool similar to
> gzip/bzip2/lzop that can be packaged and shipped by distros, and the
> output format defintion.
> Yann has some ideas for the format
Actually, I would like to use a packaged tool by distros too.
lz4demo is what I use for compressing the kernel so far.
I name it lz4 in the patch.
> For kernel, the minimum of meta information is total compressed length,
> total uncompressed length and chunk size. I don't know if the first two
> aren't stored elsewhere in the generic kernel image headers, but chunk
> size must be specified.
Right, Currently the chunk size used in the kernel decompressor is the same
as defined in lz4demo but it should have been provided as meta
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