From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751477AbeCUGlg (ORCPT ); Wed, 21 Mar 2018 02:41:36 -0400 Received: from mail-pf0-f196.google.com ([209.85.192.196]:40048 "EHLO mail-pf0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751040AbeCUGle (ORCPT ); Wed, 21 Mar 2018 02:41:34 -0400 X-Google-Smtp-Source: AG47ELvkHZmtIhgY19G+Dhl3nIJiYcobkwk3lOE02457T/DATBP6Disjir5A8OysbisIM7ozWhrX8Q== Date: Wed, 21 Mar 2018 15:41:28 +0900 From: Sergey Senozhatsky To: Maninder Singh Cc: herbert@gondor.apana.org.au, davem@davemloft.net, minchan@kernel.org, ngupta@vflare.org, sergey.senozhatsky.work@gmail.com, keescook@chromium.org, anton@enomsg.org, ccross@android.com, tony.luck@intel.com, akpm@linux-foundation.org, colin.king@canonical.com, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org, pankaj.m@samsung.com, a.sahrawat@samsung.com, v.narang@samsung.com Subject: Re: [PATCH 0/1] cover-letter/lz4: Implement lz4 with dynamic offset length. Message-ID: <20180321064128.GA468@jagdpanzerIV> References: <1521607242-3968-1-git-send-email-maninder1.s@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1521607242-3968-1-git-send-email-maninder1.s@samsung.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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