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=-10.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 AEB41C33C99 for ; Fri, 10 Jan 2020 07:16:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 808772073A for ; Fri, 10 Jan 2020 07:16:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="H9BLdLiO" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726002AbgAJHQE (ORCPT ); Fri, 10 Jan 2020 02:16:04 -0500 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:25650 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725853AbgAJHQD (ORCPT ); Fri, 10 Jan 2020 02:16:03 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1578640562; 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=vLnpFr7jsP45hCMz6lcWA2t7c8lgornfScfqptePMAA=; b=H9BLdLiOuLqEOqPV9RBLeq5pkL7RsgJCK6Dhj1Sf77Ti1e0A14/njX+rWgn1tQ+fGkhSSV dk2gBL1Wh0JiTeLkWMqGU5NiLZesTgDQIyQTIgDKFP/9hEQ/E1qZO+9/CO7lMF8veGJrcX osk7uLVYIkv40PIkzK+lmNW9v4VI76Y= 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-190-jLeurMQCPUeAZbt067BsEA-1; Fri, 10 Jan 2020 02:15:58 -0500 X-MC-Unique: jLeurMQCPUeAZbt067BsEA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C46F3107ACC5; Fri, 10 Jan 2020 07:15:57 +0000 (UTC) Received: from ming.t460p (ovpn-8-31.pek2.redhat.com [10.72.8.31]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0481760FA2; Fri, 10 Jan 2020 07:15:52 +0000 (UTC) Date: Fri, 10 Jan 2020 15:15:48 +0800 From: Ming Lei To: Guenter Roeck Cc: Jens Axboe , Christoph Hellwig , linux-block@vger.kernel.org Subject: Re: [PATCH] block: fix splitting segments Message-ID: <20200110071548.GA23264@ming.t460p> References: <20191229023230.28940-1-ming.lei@redhat.com> <20200108140248.GA2896@infradead.org> <20200109020341.GC9655@ming.t460p> <20200109071616.GA32217@infradead.org> <20200110025801.GC4501@ming.t460p> <20200110030006.GD4501@ming.t460p> <0c25bc64-d249-0b83-1d5d-6f7226293fb6@roeck-us.net> <20200110063744.GA16724@ming.t460p> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200110063744.GA16724@ming.t460p> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Fri, Jan 10, 2020 at 02:37:44PM +0800, Ming Lei wrote: > On Thu, Jan 09, 2020 at 09:10:24PM -0800, Guenter Roeck wrote: > > On 1/9/20 7:00 PM, Ming Lei wrote: > > > On Fri, Jan 10, 2020 at 10:58:01AM +0800, Ming Lei wrote: > > > > On Thu, Jan 09, 2020 at 08:18:04AM -0700, Jens Axboe wrote: > > > > > On 1/9/20 12:16 AM, Christoph Hellwig wrote: > > > > > > On Thu, Jan 09, 2020 at 10:03:41AM +0800, Ming Lei wrote: > > > > > > > It has been addressed in: > > > > > > > > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git/commit/?h=block-5.5&id=ecd255974caa45901d0b8fab03626e0a18fbc81a > > > > > > > > > > > > That is probably correct, but still highly suboptimal for most 32-bit > > > > > > architectures where physical addresses are 32 bits wide. To fix that > > > > > > the proper phys_addr_t type should be used. > > > > > > > > > > I'll swap it for phys_addr_t - we used to use dma_address_t or something > > > > > like that, but I missed this type. > > > > > > > > Guenter mentioned that 'page_to_phys(start_page) as well as offset are > > > > sometimes 0'[1]. > > > > > > > > If that(zero page physical address) can happen when phys_addr_t is 32bit, > > > > I guess phys_addr_t may not work too. > > > > > > > > Guener, could you test the patch in link[2] again? > > > > > > > > > > > > [1] https://lore.kernel.org/linux-block/20200108023822.GB28075@ming.t460p/T/#m5862216b960454fc41a85204defbb887983bfd75 > > > > [2] https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git/commit/?h=block-5.5&id=b6a89c4a9590663f80486662fe9a9c1f4cee31f4 > > > > > > Loop Guener in. > > > > > > > The patch at [2] doesn't work. > > > > My understanding is that the page in question is not mapped when > > get_max_segment_size() is called (after all, the operation is the > > result of a page fault). This is why page_to_phys() returns 0. > > page_to_phys() supposes to return page's physical address, which > should just depend on this machine's physical address space, > not related with page mapping. > > I understand physical address 0 might be valid, such as the 1st > page frame of ram. > > > > > You'll either need a local u64 variable, or use some other means > > to handle that situation. Something like > > > > phys_addr_t paddr = page_to_phys(start_page); > > > > if (paddr == 0) > > return queue_max_segment_size(q); > > > > at the beginning of the function might do, though there might > > still be a problem when the page is later assigned and crosses > > a segment boundary (if that is possible). > > IMO, zero physical address case is the only corner case not > covered by using 'phys_addr_t'. If phys_addr_t is 32bit, sum of > page_to_phys(start_page) and offset shouldn't be >= 4G. Or could you test the following patch? diff --git a/block/blk-merge.c b/block/blk-merge.c index 347782a24a35..d1bed8c382bf 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -164,8 +164,13 @@ static inline unsigned get_max_segment_size(const struct request_queue *q, unsigned long mask = queue_segment_boundary(q); offset = mask & (page_to_phys(start_page) + offset); - return min_t(unsigned long, mask - offset + 1, - queue_max_segment_size(q)); + + /* + * overflow may be triggered in case of zero page physical address + * on 32bit arch, use queue's max segment size when that happens + */ + return min_not_zero(mask - offset + 1, + (unsigned long)queue_max_segment_size(q)); } /** Thanks, Ming