From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 09F3AC43610 for ; Mon, 19 Nov 2018 08:19:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D05C820823 for ; Mon, 19 Nov 2018 08:19:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D05C820823 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-btrfs-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726956AbeKSSmo (ORCPT ); Mon, 19 Nov 2018 13:42:44 -0500 Received: from mx1.redhat.com ([209.132.183.28]:57698 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726784AbeKSSmo (ORCPT ); Mon, 19 Nov 2018 13:42:44 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 46775307D91A; Mon, 19 Nov 2018 08:19:50 +0000 (UTC) Received: from ming.t460p (ovpn-8-26.pek2.redhat.com [10.72.8.26]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E334B5D70A; Mon, 19 Nov 2018 08:19:28 +0000 (UTC) Date: Mon, 19 Nov 2018 16:19:24 +0800 From: Ming Lei To: Christoph Hellwig Cc: Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Dave Chinner , Kent Overstreet , Mike Snitzer , dm-devel@redhat.com, Alexander Viro , linux-fsdevel@vger.kernel.org, Shaohua Li , linux-raid@vger.kernel.org, linux-erofs@lists.ozlabs.org, David Sterba , linux-btrfs@vger.kernel.org, "Darrick J . Wong" , linux-xfs@vger.kernel.org, Gao Xiang , Theodore Ts'o , linux-ext4@vger.kernel.org, Coly Li , linux-bcache@vger.kernel.org, Boaz Harrosh , Bob Peterson , cluster-devel@redhat.com Subject: Re: [PATCH V10 08/19] btrfs: move bio_pages_all() to btrfs Message-ID: <20181119081922.GB16736@ming.t460p> References: <20181115085306.9910-1-ming.lei@redhat.com> <20181115085306.9910-9-ming.lei@redhat.com> <20181116133845.GG3165@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181116133845.GG3165@lst.de> User-Agent: Mutt/1.9.1 (2017-09-22) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.48]); Mon, 19 Nov 2018 08:19:50 +0000 (UTC) Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Fri, Nov 16, 2018 at 02:38:45PM +0100, Christoph Hellwig wrote: > On Thu, Nov 15, 2018 at 04:52:55PM +0800, Ming Lei wrote: > > BTRFS is the only user of this helper, so move this helper into > > BTRFS, and implement it via bio_for_each_segment_all(), since > > bio->bi_vcnt may not equal to number of pages after multipage bvec > > is enabled. > > btrfs only uses the value to check if it is larger than 1. No amount > of multipage bio merging should ever make bi_vcnt go from 0 to 1 or > vice versa. Could you explain a bit why? Suppose 2 physically continuous pages are added to this bio, .bi_vcnt can be 1 in case of multi-page bvec, but it is 2 in case of single-page bvec. Thanks, Ming