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    SubjectRe: [RFC PATCH 0/4] Add support for LZ4-compressed kernels
    On 2013-01-30 오전 7:55, David Sterba wrote:
    > On Sat, Jan 26, 2013 at 02:50:43PM +0900, Kyungsik Lee wrote:
    >> This patchset is for supporting LZ4 compressed kernel and initial ramdisk on
    >> the x86 and ARM architectures.
    > Have you considered the 'high compression' mode of lz4?
    > http://code.google.com/p/lz4/source/browse/trunk/lz4hc.c
    >
    > The compression format remains the same, the compressor tries harder
    > (but is slower), resulting compression ratio is better.
    >
    > an examle compression for vmlinux.bin of x86_64 build:
    >
    > input size: 16509520 bytes
    >
    > lz4 (svn 88):
    > output size: 6393684 (38.7%)
    > compression time: 41.7 ms (395 MB/s)
    > decompression time: 13.7 ms (1204 MB/s)
    >
    > lz4hc (svn 88):
    > output size: 5319137 (32.2%)
    > compression time: 683 ms (24 MB/s)
    > decompression time: 13.1 ms (1259 MB/s)
    >
    > compressed file delta: 6393684 - 5319137 = 1074547 ~ 1MB
    >
    > tested on a Nehalem box; same test on my slow desktop gives
    >
    > lz4:
    > compression time: 97 ms (169 MB/s)
    > decompression time: 25.7 ms (643 MB/s)
    >
    > lz4hc:
    > compression time: 1386 ms (11 MB/s)
    > decompression time: 26 ms (619 MB/s)
    >
    > While the decompression time is almost the same, image size is smaller.
    > The kernel image compression is run in userspace and the low speed is
    > not much of concern for a one-time operation.
    >
    > For the reference, lzo (current kernel version) run on the destktop:
    >
    > output size: 6026256 (36.5%)
    > decompression time: 79.6 ms (207 MB/s)
    >
    >> It seems that it’s worth trying LZ4 compressed kernel image or ramdisk
    >> for making the kernel boot more faster.
    > There's another potential user of lz4: btrfs. I've submitted a feature
    > preview integrating lz4 compression
    > http://thread.gmane.org/gmane.comp.file-systems.btrfs/15744
    > and we have tried to integrate the HC mode as well
    > http://thread.gmane.org/gmane.comp.file-systems.btrfs/18165
    > .
    > So far it's on a slow track, conceptually it works, but I the code needs
    > some work so it could live under lib/* (we've used the svn sources
    > with minor changes, no kernel coding style). It would be easier for me
    > to enhance the existing lib/lz4/* codebase.
    >
    > Also zram could consider lz4, I'm not sure if there are other potential
    > users.
    Yes, I guess squash fs and crypto would also benefit from lz4.


    Thanks,
    Kyungsik



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