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=-7.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 27BE9C4361A for ; Fri, 4 Dec 2020 04:01:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B3972222B6 for ; Fri, 4 Dec 2020 04:01:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726316AbgLDEBO (ORCPT ); Thu, 3 Dec 2020 23:01:14 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:26506 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725793AbgLDEBN (ORCPT ); Thu, 3 Dec 2020 23:01:13 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1607054387; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=iemAarVTYer669NqYpfSNlhAQOnlEJ+C0/QP5pt/RtU=; b=ApoiIcgN98xv4C0YEie94oQlXqZsbm/Xj+aujcXLdRlKV825zHtY3frS+FOfjFadA5vZ06 3x2rUnC2gLB0T3nC6kakZoFpxwggvwuaW/tdxZkkfoZY5C3V6/WCG9KWMxSywTBLZti6BM WiwcvawiX6U2fUdMhJANpE3oKGFMduI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-60-kpnPDRvGMcKzo2D404NQSQ-1; Thu, 03 Dec 2020 22:59:45 -0500 X-MC-Unique: kpnPDRvGMcKzo2D404NQSQ-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 886451005504; Fri, 4 Dec 2020 03:59:44 +0000 (UTC) Received: from T590 (ovpn-12-155.pek2.redhat.com [10.72.12.155]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 244A05C1CF; Fri, 4 Dec 2020 03:59:28 +0000 (UTC) Date: Fri, 4 Dec 2020 11:59:24 +0800 From: Ming Lei To: Mike Snitzer Cc: axboe@kernel.dk, martin.petersen@oracle.com, linux-block@vger.kernel.org, dm-devel@redhat.com, jdorminy@redhat.com, bjohnsto@redhat.com Subject: Re: [PATCH v2] block: use gcd() to fix chunk_sectors limit stacking Message-ID: <20201204035924.GD661914@T590> References: <20201130171805.77712-1-snitzer@redhat.com> <20201201160709.31748-1-snitzer@redhat.com> <20201203032608.GD540033@T590> <20201203143359.GA29261@redhat.com> <20201204011243.GB661914@T590> <20201204020343.GA32150@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201204020343.GA32150@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Thu, Dec 03, 2020 at 09:03:43PM -0500, Mike Snitzer wrote: > On Thu, Dec 03 2020 at 8:12pm -0500, > Ming Lei wrote: > > > On Thu, Dec 03, 2020 at 09:33:59AM -0500, Mike Snitzer wrote: > > > On Wed, Dec 02 2020 at 10:26pm -0500, > > > Ming Lei wrote: > > > > > > > On Tue, Dec 01, 2020 at 11:07:09AM -0500, Mike Snitzer wrote: > > > > > commit 22ada802ede8 ("block: use lcm_not_zero() when stacking > > > > > chunk_sectors") broke chunk_sectors limit stacking. chunk_sectors must > > > > > reflect the most limited of all devices in the IO stack. > > > > > > > > > > Otherwise malformed IO may result. E.g.: prior to this fix, > > > > > ->chunk_sectors = lcm_not_zero(8, 128) would result in > > > > > blk_max_size_offset() splitting IO at 128 sectors rather than the > > > > > required more restrictive 8 sectors. > > > > > > > > What is the user-visible result of splitting IO at 128 sectors? > > > > > > The VDO dm target fails because it requires IO it receives to be split > > > as it advertised (8 sectors). > > > > OK, looks VDO's chunk_sector limit is one hard constraint, even though it > > is one DM device, so I guess you are talking about DM over VDO? > > > > Another reason should be that VDO doesn't use blk_queue_split(), otherwise it > > won't be a trouble, right? > > > > Frankly speaking, if the stacking driver/device has its own hard queue limit > > like normal hardware drive, the driver should be responsible for the splitting. > > DM core does the splitting for VDO (just like any other DM target). > In 5.9 I updated DM to use chunk_sectors, use blk_stack_limits() > stacking of it, and also use blk_max_size_offset(). > > But all that block core code has shown itself to be too rigid for DM. I > tried to force the issue by stacking DM targets' ti->max_io_len with > chunk_sectors. But really I'd need to be able to pass in the per-target > max_io_len to blk_max_size_offset() to salvage using it. > > Stacking chunk_sectors seems ill-conceived. One size-fits-all splitting > is too rigid. DM/VDO knows exactly it is one hard chunk_sectors limit, and DM shouldn't play the stacking trick on VDO's chunk_sectors limit, should it? Thanks, Ming