Re: [PATCH 0/2] Squashfs: add LZ4 compression

[Phillip Lougher]

On 22 July 2013 04:05, Gu Zheng <guz.fnst@xxxxxxxxxxxxxx> wrote:
> Hi Phillip,
>         Have some tests been carried out to confirm that Squashfs really
> can get benefit from LZ4 compression, comparing with lzo?

This seems to be a loaded question, in that it seems to be trying to
reopen the "why add lz4 when we already have lzo" debate all over
again.  As LZ4 has been merged to mainline, this appears to be a
question that has already been answered.

As far as Squashfs is concerned,  I believe it is important to give
people the choice of using LZ4 to compress Squashfs filesystems now
its been mainlined.  As far as expected benefits are concerned,
Squashfs' use in embedded systems is very similar to compressing
kernels and initramfs data, in that it tends to be used to compress
root filesystems.  As such the benefits of using LZ4 in Squashfs
should be broadly similar to using LZ4 to compress kernels and
initramfs data.  Ultimately it is up to people to experiment and
choose whatever compression is best for their systems.

People are welcome to try the patches out and report their findings.

Phillip

>
> Thanks,
> Gu
>
> On 07/22/2013 10:21 AM, Phillip Lougher wrote:
>
>> Hi
>>
>> Now that LZ4 compression support is in 3.11-rc1, I have written the
>> following two patches for Squashfs to use it.
>>
>> Phillip Lougher (2):
>>   Squashfs: add LZ4 compression support
>>   Squashfs: Add LZ4 compression configuration option
>>
>>  Documentation/filesystems/squashfs.txt |    8 +-
>>  fs/squashfs/Kconfig                    |   15 +++
>>  fs/squashfs/Makefile                   |    1 +
>>  fs/squashfs/decompressor.c             |    7 ++
>>  fs/squashfs/decompressor.h             |    4 +
>>  fs/squashfs/lz4_wrapper.c              |  163 ++++++++++++++++++++++++++++++++
>>  fs/squashfs/squashfs_fs.h              |    1 +
>>  7 files changed, 195 insertions(+), 4 deletions(-)
>>  create mode 100644 fs/squashfs/lz4_wrapper.c
>>
>> These patches are also available in the git tree here:
>>
>> browse: https://git.kernel.org/cgit/linux/kernel/git/pkl/squashfs-lz4.git
>> git clone: git://git.kernel.org/pub/scm/linux/kernel/git/pkl/squashfs-lz4.git
>>
>> LZ4 support has (obviously) also been added to the squashfs-tools
>> (Mksquashfs and Unsquashfs).  This is available from the Squashfs-tools
>> git repository here:
>>
>> browse: https://git.kernel.org/cgit/fs/squashfs/squashfs-tools.git
>> git clone: git://git.kernel.org/pub/scm/fs/squashfs/squashfs-tools.git
>>
>> When building the squashfs-tools edit the Makefile to enable LZ4
>> support (by default it is disabled).
>>
>> LZ4 compression can be specified by using the -comp option, e.g.
>> % mksquashfs xxx img.sqsh -comp lz4
>>
>> The use of LZ4 high compression can be specified using -Xhc, e.g.
>>
>> % mksquashfs xxx img.sqsh -comp lz4 -Xhc
>>
>> Phillip
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