Re: [PATCH 0/1] cover-letter/lz4: Implement lz4 with dynamic offset length.

Maninder Singh
2018-04-02T06:08:35Z

Hello,

>> (Added cover letter to avoid much text in patch description)
>>
>> LZ4 specification defines 2 byte offset length for 64 KB data.
>> But in case of ZRAM we compress data per page and in most of
>> architecture PAGE_SIZE is 4KB. So we can decide offset length based
>> on actual offset value. For this we can reserve 1 bit to decide offset
>> length (1 byte or 2 byte). 2 byte required only if ofsset is greater than 127,
>> else 1 byte is enough.
>
>So what happens if I compress the data on a system with no dyn
>offset and then send it over the network to a machine which has
>dyn offset? Or, say, I have a USB stick with a compression enabled
>FS, store files on a dyn offset enabled PC and then mount that USB
>stick on a machine with no dyn offset support. And vice versa.

lz4_dyn is not an extension of LZ4 so there is no backward compatibility.
Consider this as a different algorithm adapted from LZ4 for better compression ratio.

Thanks
Maninder Singh