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 E07E6C04EBB for ; Thu, 22 Nov 2018 10:32:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AB85420684 for ; Thu, 22 Nov 2018 10:32:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AB85420684 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-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405355AbeKVVLf (ORCPT ); Thu, 22 Nov 2018 16:11:35 -0500 Received: from mx1.redhat.com ([209.132.183.28]:34264 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388243AbeKVVLf (ORCPT ); Thu, 22 Nov 2018 16:11:35 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id B03862D2BEB; Thu, 22 Nov 2018 10:32:45 +0000 (UTC) Received: from ming.t460p (ovpn-8-23.pek2.redhat.com [10.72.8.23]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 26F795C25A; Thu, 22 Nov 2018 10:32:13 +0000 (UTC) Date: Thu, 22 Nov 2018 18:32:09 +0800 From: Ming Lei To: Christoph Hellwig Cc: Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Theodore Ts'o , Omar Sandoval , Sagi Grimberg , Dave Chinner , Kent Overstreet , Mike Snitzer , dm-devel@redhat.com, Alexander Viro , linux-fsdevel@vger.kernel.org, Shaohua Li , linux-raid@vger.kernel.org, David Sterba , linux-btrfs@vger.kernel.org, "Darrick J . Wong" , linux-xfs@vger.kernel.org, Gao Xiang , linux-ext4@vger.kernel.org, Coly Li , linux-bcache@vger.kernel.org, Boaz Harrosh , Bob Peterson , cluster-devel@redhat.com Subject: Re: [PATCH V11 14/19] block: handle non-cluster bio out of blk_bio_segment_split Message-ID: <20181122103208.GD27273@ming.t460p> References: <20181121032327.8434-1-ming.lei@redhat.com> <20181121032327.8434-15-ming.lei@redhat.com> <20181121143355.GB2594@lst.de> <20181121153726.GC19111@ming.t460p> <20181121174621.GA6961@lst.de> <20181122093259.GA27007@ming.t460p> <20181122100427.GA28871@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181122100427.GA28871@lst.de> User-Agent: Mutt/1.9.1 (2017-09-22) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Thu, 22 Nov 2018 10:32:46 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 22, 2018 at 11:04:28AM +0100, Christoph Hellwig wrote: > On Thu, Nov 22, 2018 at 05:33:00PM +0800, Ming Lei wrote: > > However, using virt boundary limit on non-cluster seems over-kill, > > because the bio will be over-split(each small bvec may be split as one bio) > > if it includes lots of small segment. > > The combination of the virt boundary of PAGE_SIZE - 1 and a > max_segment_size of PAGE_SIZE will only split if the to me merged > segment is in a different page than the previous one, which is exactly > what we need here. Multiple small bvec inside the same page (e.g. > 512 byte buffer_heads) will still be merged. > > > What we want to do is just to avoid to merge bvecs to segment, which > > should have been done by NO_SG_MERGE simply. However, after multi-page > > is enabled, two adjacent bvecs won't be merged any more, I just forget > > to remove the bvec merge code in V11. > > > > So seems we can simply avoid to use virt boundary limit for non-cluster > > after multipage bvec is enabled? > > No, we can't just remove it. As explained in the patch there is one very > visible difference of setting the flag amd that is no segment will span a > page boundary, and at least the iSCSI code seems to rely on that. IMO, we should use queue_segment_boundary() to enhance the rule during splitting segment after multi-page bvec is enabled. Seems we miss the segment boundary limit in bvec_split_segs(). Thanks, Ming