From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752312AbbANAXj (ORCPT ); Tue, 13 Jan 2015 19:23:39 -0500 Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:52673 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751086AbbANAXh (ORCPT ); Tue, 13 Jan 2015 19:23:37 -0500 Message-ID: <54B5B6E4.4020400@fb.com> Date: Tue, 13 Jan 2015 17:23:00 -0700 From: Jens Axboe User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Richard Weinberger , Christoph Hellwig CC: , , , , , Subject: Re: [PATCH 2/2 v2] UBI: Block: Add blk-mq support References: <1420926734-16417-1-git-send-email-richard@nod.at> <1420926734-16417-2-git-send-email-richard@nod.at> <20150113162553.GA24351@infradead.org> <54B5A188.2000001@nod.at> <54B5A213.1090502@fb.com> <54B5A77C.9040405@nod.at> <54B5AA84.9010306@fb.com> <54B5AC10.6070102@nod.at> In-Reply-To: <54B5AC10.6070102@nod.at> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [192.168.57.29] X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.13.68,1.0.33,0.0.0000 definitions=2015-01-13_08:2015-01-13,2015-01-13,1970-01-01 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 kscore.is_bulkscore=0 kscore.compositescore=0 circleOfTrustscore=0 compositescore=0.160988131301636 urlsuspect_oldscore=0.160988131301636 suspectscore=0 recipient_domain_to_sender_totalscore=0 phishscore=0 bulkscore=0 kscore.is_spamscore=0 recipient_to_sender_totalscore=0 recipient_domain_to_sender_domain_totalscore=1996008 rbsscore=0.160988131301636 spamscore=0 recipient_to_sender_domain_totalscore=4 urlsuspectscore=0.9 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=7.0.1-1402240000 definitions=main-1501140003 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/13/2015 04:36 PM, Richard Weinberger wrote: > > > Am 14.01.2015 um 00:30 schrieb Jens Axboe: >>> If I understand you correctly it can happen that blk_rq_bytes() returns >>> more bytes than blk_rq_map_sg() allocated, right? >> >> No, the number of bytes will be the same, no magic is involved :-) > > Good to know. :) > >> But lets say the initial request has 4 bios, with each 2 pages, for a >> total of 8 segments. Lets further assume that the pages in each bio are >> contiguous, so that blk_rq_map_sg() will map this to 4 sg elements, each >> 2xpages long. >> >> Now, this may already be handled just fine, and you don't need to >> update/store the actual sg count. I just looked at the source, and I'm >> assuming it'll do the right thing (ubi_read_sg() will bump the active sg >> element, when that size has been consumed), but I don't have >> ubi_read_sg() in my tree to verify. > > Currently the sg count is hard coded to UBI_MAX_SG_COUNT. The max count doesn't matter, that just provides you a guarantee that you'll never receive a request that maps to more than that. The point I'm trying to make is that if you receive 8 segments and it maps to 4, then you better not look at segments 5..8 after it being mapped. Whatever the max is, doesn't matter in this conversation. > I'm sorry, I forgot to CC you and hch to this patch: Which is as I suspected, you'll do each segment to the length specified, hence you don't need to track the returned count from blk_rq_map_sg(). -- Jens Axboe