From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752511AbdF2Irm (ORCPT ); Thu, 29 Jun 2017 04:47:42 -0400 Received: from LGEAMRELO13.lge.com ([156.147.23.53]:56221 "EHLO lgeamrelo13.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751894AbdF2Irb (ORCPT ); Thu, 29 Jun 2017 04:47:31 -0400 X-Original-SENDERIP: 156.147.1.151 X-Original-MAILFROM: minchan@kernel.org X-Original-SENDERIP: 10.177.220.163 X-Original-MAILFROM: minchan@kernel.org Date: Thu, 29 Jun 2017 17:47:26 +0900 From: Minchan Kim To: Sergey Senozhatsky Cc: Andrew Morton , linux-kernel@vger.kernel.org, Juneho Choi , kernel-team Subject: Re: [PATCH v1 0/7] writeback incompressible pages to storage Message-ID: <20170629084726.GB22335@bbox> References: <1498459987-24562-1-git-send-email-minchan@kernel.org> <20170628154157.GA528@tigerII.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170628154157.GA528@tigerII.localdomain> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Sergey, On Thu, Jun 29, 2017 at 12:41:57AM +0900, Sergey Senozhatsky wrote: > Hello, > > On (06/26/17 15:52), Minchan Kim wrote: > [..] > > zRam is useful for memory saving with compressible pages but sometime, > > workload can be changed and system has lots of incompressible pages > > which is very harmful for zram. > > could do. that makes zram quite complicated, to be honest. no offense, > but the whole zram's "good compression" margin looks to me completely > random and quite unreasonable. building a complex logic atop of random > logic is a bit tricky. but I see what problem you are trying to address. > > > This patch supports writeback feature of zram so admin can set up > > a block device and with it, zram can save the memory via writing > > out the incompressile pages once it found it's incompressible pages > > (1/4 comp ratio) instead of keeping the page in memory. > > hm, alternative idea. just an idea. can we try compressing the page > with another algorithm? example: downcast from lz4 to zlib? we can > set up a fallback "worst case" algorithm, so each entry can contain > additional flag that would tell if the src page was compressed with > the fast or slow algorithm. that sounds to me easier than "create a > new block device and bond it to zram, etc". but I may be wrong. We tried it although it was static not dynamic adatation you suggested. However problem was media-stream data so zlib, lzam added just pointless overhead. Thanks.