From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754938AbdBPNkO (ORCPT ); Thu, 16 Feb 2017 08:40:14 -0500 Received: from mx2.suse.de ([195.135.220.15]:58878 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754386AbdBPNkL (ORCPT ); Thu, 16 Feb 2017 08:40:11 -0500 Subject: Re: [PATCH 02/17] block: introduce bio_remove_last_page() To: Ming Lei References: <1487245547-24384-1-git-send-email-tom.leiming@gmail.com> <1487245547-24384-3-git-send-email-tom.leiming@gmail.com> Cc: Shaohua Li , Jens Axboe , Linux Kernel Mailing List , "open list:SOFTWARE RAID (Multiple Disks) SUPPORT" , linux-block , Christoph Hellwig , NeilBrown From: Johannes Thumshirn Message-ID: Date: Thu, 16 Feb 2017 14:40:05 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/16/2017 02:30 PM, Ming Lei wrote: > On Thu, Feb 16, 2017 at 8:08 PM, Johannes Thumshirn wrote: >> On 02/16/2017 12:45 PM, Ming Lei wrote: >>> MD need this helper to remove the last added page, so introduce >>> it. >>> >>> Signed-off-by: Ming Lei >>> --- >>> block/bio.c | 23 +++++++++++++++++++++++ >>> include/linux/bio.h | 1 + >>> 2 files changed, 24 insertions(+) >>> >>> diff --git a/block/bio.c b/block/bio.c >>> index 5eec5e08417f..0ce7ffcd7939 100644 >>> --- a/block/bio.c >>> +++ b/block/bio.c >>> @@ -837,6 +837,29 @@ int bio_add_pc_page(struct request_queue *q, struct bio *bio, struct page >>> EXPORT_SYMBOL(bio_add_pc_page); >>> >>> /** >>> + * bio_remove_last_page - remove the last added page >>> + * @bio: destination bio >>> + * >>> + * Attempt to remove the last added page from the bio_vec maplist. >>> + */ >>> +void bio_remove_last_page(struct bio *bio) >>> +{ >>> + /* >>> + * cloned bio must not modify vec list >>> + */ >>> + if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED))) >>> + return; >>> + >>> + if (bio->bi_vcnt > 0) { >> >> In patch 1 you introduce bio_segments_all() with the log message 'So >> that we can replace the direct access to .bi_vcnt.' Here you introduce a >> new direct access to it (plus the duplicated WARN_ON_ONCE()). >> >> Maybe use the helper directly here (I admit I haven't gone through the >> whole series yet, so I can't see if the change is made later). > > Firstly MD does need one helper to remove the last added page, as you > can see there are three such uses in patch3. > > Secondly both the two helpers will be changed once multipage bvec > is supported, that means we have to change MD too after multipage bvec > if just using bio_segments_all() to replace .bi_vcnt for removing > the last added page. I'm not sure if we're talking past each other here, I assumed you'd do something like: void bio_remove_last_page(struct bio *bio) { int vcnt = bio_segments_all(bio); if (bio_flagged(bio, BIO_CLONED)) return; if (vcnt > 0) { struct bio_vec *bv = &bio->bi_io_vec[vcnt - 1]; bio->bi_iter.bi_size -= bv->bv_len; bio->bi_vcnt--; } } -- Johannes Thumshirn Storage jthumshirn@suse.de +49 911 74053 689 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: Felix Imendörffer, Jane Smithard, Graham Norton HRB 21284 (AG Nürnberg) Key fingerprint = EC38 9CAB C2C4 F25D 8600 D0D0 0393 969D 2D76 0850