Bug#549681: bug#549681: mkvmlinuz: use xz to compress vmlinuz-boxed initrd

[Touko Korpela <touko.korpela@iki.fi>]

On Sat, Jun 30, 2012 at 11:01:47PM -0400, Milan Kupcevic wrote:
> The attached patch brings vmlinuz from about 13MB to about 9.5MB, which
> is well under the 12MB limit. Downside is that xz compressing is
> noticeably slower than currently used gzip, but decompressing speed
> difference is not noticeable.
> 
> I've tested it on Pegasos II machine, it boots really fast. Updated
> mkvmlinuz package is waiting on mentors.debian.net for a willing sponsor
> for upload.
> ...
> +if test "$post_2_6_38"; then
> +  XZ="xz --check=crc32 -8"
> +else
> +  XZ=false
> +fi

>From xz(1) manual page (you can ignore DecMem):
                     Preset   DictSize   CompCPU   CompMem   DecMem
                       -0     256 KiB       0        3 MiB    1 MiB
                       -1       1 MiB       1        9 MiB    2 MiB
                       -2       2 MiB       2       17 MiB    3 MiB
                       -3       4 MiB       3       32 MiB    5 MiB
                       -4       4 MiB       4       48 MiB    5 MiB
                       -5       8 MiB       5       94 MiB    9 MiB
                       -6       8 MiB       6       94 MiB    9 MiB
                       -7      16 MiB       6      186 MiB   17 MiB
                       -8      32 MiB       6      370 MiB   33 MiB
                       -9      64 MiB       6      674 MiB   65 MiB

Better to use default setting "-6" that has lower memory requirement.