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Date: Fri, 03 Mar 2017 20:07:01 +0900
From: Hyunchul Lee <hyc.lee@gmail.com>
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To: Richard Weinberger <richard@nod.at>
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Subject: Re: [PATCH 0/3] ubifs: add lz4hc compression
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Hi, Ricard

On 03/03/2017 05:08 PM, Richard Weinberger wrote:
> Hyunchul Lee,
> 
> Am 28.02.2017 um 06:16 schrieb Hyunchul Lee:
>> From: Hyunchul Lee <cheol.lee@lge.com>
>>
>> This patch set is for adding support for lz4hc compression.  lz4hc's
>> compression ratio is comparable to zlib, but its compression/decompression
>> speed is faster than zlib[1].
> 
> Do you have performance numbers that show the speedup on a common embedded
> system with NAND?

I am trying to build environment for a common embedded system with NAND. 
if I am done, I will report the performance result. 

> 
>> Another compression type cannot be added any more in respect that type of
>> ubifs_inode's compr_type is "unsigned:2" and there are 4 compression
>> types.  There may be overflow in assignment to compr_type, and prevision 
>> version of ubifs is trying to decompress file with wrong compression type.
> 
> As Artem noted this is only an in-memory struct.
> 
> What happens when you compress a file with lz4hc and try to access this
> UBIFS file with an older kernel?
> AFAICT ubifs_iget() will notice and return -EINVAL but please double check.
> 

yes, ubifs detects this. but I mean that if another compression type except lz4hc
is added, ubifs cannot. because ubifs_iget() assigns ubifs_ino_node's compr_type(16-bit) 
to ubifs_inode's compr_type(2-bit).
I guess that the disk format version should be incremented.

> Thanks,
> //richard
> 

Thanks,
Hyunchul