From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932517AbdDQCPc (ORCPT ); Sun, 16 Apr 2017 22:15:32 -0400 Received: from LGEAMRELO13.lge.com ([156.147.23.53]:37566 "EHLO lgeamrelo13.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932320AbdDQCPa (ORCPT ); Sun, 16 Apr 2017 22:15:30 -0400 X-Original-SENDERIP: 156.147.1.127 X-Original-MAILFROM: minchan@kernel.org X-Original-SENDERIP: 165.244.249.23 X-Original-MAILFROM: minchan@kernel.org X-Original-SENDERIP: 10.177.223.161 X-Original-MAILFROM: minchan@kernel.org Date: Mon, 17 Apr 2017 11:14:39 +0900 From: Minchan Kim To: Sergey Senozhatsky CC: Andrew Morton , , , , Sergey Senozhatsky Subject: Re: [PATCH 1/3] zram: fix operator precedence to get offset Message-ID: <20170417021439.GA20981@bbox> References: <1492042622-12074-1-git-send-email-minchan@kernel.org> <20170414050747.GB462@jagdpanzerIV.localdomain> <20170414153251.GA16910@bgram> <20170417012105.GA518@jagdpanzerIV.localdomain> <20170417015429.GE518@jagdpanzerIV.localdomain> MIME-Version: 1.0 In-Reply-To: <20170417015429.GE518@jagdpanzerIV.localdomain> User-Agent: Mutt/1.5.24 (2015-08-30) X-MIMETrack: Itemize by SMTP Server on LGEKRMHUB06/LGE/LG Group(Release 8.5.3FP6|November 21, 2013) at 2017/04/17 11:14:41, Serialize by Router on LGEKRMHUB06/LGE/LG Group(Release 8.5.3FP6|November 21, 2013) at 2017/04/17 11:14:41, Serialize complete at 2017/04/17 11:14:41 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Sergey, On Mon, Apr 17, 2017 at 10:54:29AM +0900, Sergey Senozhatsky wrote: > On (04/17/17 10:21), Sergey Senozhatsky wrote: > > > However, it should be *fixed* to prevent confusion in future > > or may be something like below? can save us some cycles. > > remove this calculation > > - offset = sector & (SECTORS_PER_PAGE - 1) << SECTOR_SHIFT; > > > and pass 0 to zram_bvec_rw() > > - err = zram_bvec_rw(zram, &bv, index, offset, is_write); > + err = zram_bvec_rw(zram, &bv, index, 0, is_write); That was one I wrote but have thought it more. Because I suspect fs can submit page-size IO in non-aligned PAGE_SIZE sector? For example, it can submit PAGE_SIZE read request from 9 sector. Is it possible? I don't know. As well, FS can format zram from sector 1, not sector 0? IOW, can't it use starting sector as non-page algined sector? We can do it via fdisk? Anyway, If one of scenario I mentioned is possible, zram_rw_page will be broken. If it's hard to check all of scenario in this moment, it would be better to not remove it and then add WARN_ON(offset) in there. While I am writing this, I found this. /** * bdev_read_page() - Start reading a page from a block device * @bdev: The device to read the page from * @sector: The offset on the device to read the page to (need not be aligned) * @page: The page to read * Hmm,, need investigation but no time.