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

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Date:	Mon, 22 Jul 2013 14:04:59 +0800
From:	Gu Zheng <guz.fnst@...fujitsu.com>
To:	Phillip Lougher <phillip.lougher@...il.com>
CC:	Phillip Lougher <phillip@...ashfs.org.uk>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-embedded@...r.kernel.org
Subject: Re: [PATCH 0/2] Squashfs: add LZ4 compression

On 07/22/2013 01:07 PM, Phillip Lougher wrote:

> On 22 July 2013 04:05, Gu Zheng <guz.fnst@...fujitsu.com> 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.

No, they are different. LZ4 can be merged to mainline, because we can
see the benefit(faster compressing speed under the enabled unaligned 
memory access) it brings to us comparing with lzo. 
But it's hard to say that it also really can bring benefit to Squashfs.

> 
> 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.

Yes, but the premise is that using LZ4 in Squashfs is better than lzo
in at least one actual situation.

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

Let's look and see other guys' feedbacks, they are more persuasive.:)

Regards,
Gu

> 
> 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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>>
>>
> 


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