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

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Date:   Wed, 21 Mar 2018 15:41:28 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Maninder Singh <maninder1.s@...sung.com>
Cc:     herbert@...dor.apana.org.au, davem@...emloft.net,
        minchan@...nel.org, ngupta@...are.org,
        sergey.senozhatsky.work@...il.com, keescook@...omium.org,
        anton@...msg.org, ccross@...roid.com, tony.luck@...el.com,
        akpm@...ux-foundation.org, colin.king@...onical.com,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        pankaj.m@...sung.com, a.sahrawat@...sung.com, v.narang@...sung.com
Subject: Re: [PATCH 0/1] cover-letter/lz4: Implement lz4 with dynamic offset
 length.

On (03/21/18 10:10), Maninder Singh wrote:
> (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.

	-ss