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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 E43C9C10DCE for ; Thu, 12 Mar 2020 12:34:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B9C8C206E7 for ; Thu, 12 Mar 2020 12:34:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Wbj5fAZB" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726302AbgCLMeb (ORCPT ); Thu, 12 Mar 2020 08:34:31 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:39975 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726299AbgCLMea (ORCPT ); Thu, 12 Mar 2020 08:34:30 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1584016468; 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=Aq5ynHWp3a1dNNzDlF2bQ3ak1ZRxNfcBoMq41RZPyZg=; b=Wbj5fAZBusREhkJaJ56vyih73ab8e5WWOuviIn8nepxvd56i+mbgdhXvzcUTLyyIPpoxz6 sXBgV0ZYHvYeR0xCqRFCUZs3FuTNHKbJtNV2Hdzh4vdxUz2AfPQTKfKNCg/uq0pJPvQmjR deCdp1vE4Z4gq0SIIgonOS6kDyCn7uA= 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-58-J2TaXc-FPUOgUSjildFoSw-1; Thu, 12 Mar 2020 08:34:26 -0400 X-MC-Unique: J2TaXc-FPUOgUSjildFoSw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 93EC98017CC; Thu, 12 Mar 2020 12:34:25 +0000 (UTC) Received: from ming.t460p (ovpn-8-19.pek2.redhat.com [10.72.8.19]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E8D5090CFF; Thu, 12 Mar 2020 12:34:20 +0000 (UTC) Date: Thu, 12 Mar 2020 20:34:15 +0800 From: Ming Lei To: Feng Li Cc: linux-block@vger.kernel.org Subject: Re: [Question] IO is split by block layer when size is larger than 4k Message-ID: <20200312123415.GA7660@ming.t460p> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Thu, Mar 12, 2020 at 07:13:28PM +0800, Feng Li wrote: > Hi experts, > > May I ask a question about block layer? > When running fio in guest os, I find a 256k IO is split into the page > by page in bio, saved in bvecs. > And virtio-blk just put the bio_vec one by one in the available > descriptor table. > > So if my backend device does not support iovector > opertion(preadv/pwritev), then IO is issued to a low layer page by > page. > My question is: why doesn't the bio save multi-pages in one bio_vec? We start multipage bvec since v5.1, especially since 07173c3ec276 ("block: enable multipage bvecs"). Thanks, Ming