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=-2.3 required=3.0 tests=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 CFC36C43331 for ; Mon, 11 Nov 2019 10:22:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AB97620674 for ; Mon, 11 Nov 2019 10:22:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726791AbfKKKWH (ORCPT ); Mon, 11 Nov 2019 05:22:07 -0500 Received: from verein.lst.de ([213.95.11.211]:48568 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726768AbfKKKWH (ORCPT ); Mon, 11 Nov 2019 05:22:07 -0500 Received: by verein.lst.de (Postfix, from userid 2407) id 17E2E68BE1; Mon, 11 Nov 2019 11:22:00 +0100 (CET) Date: Mon, 11 Nov 2019 11:21:59 +0100 From: Christoph Hellwig To: Ming Lei Cc: Jens Axboe , linux-block@vger.kernel.org, Christoph Hellwig Subject: Re: [RFC PATCH 2/2] block: split bio if the only bvec's length is > SZ_4K Message-ID: <20191111102159.GA12709@lst.de> References: <20191108101528.31735-1-ming.lei@redhat.com> <20191108101528.31735-3-ming.lei@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191108101528.31735-3-ming.lei@redhat.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Fri, Nov 08, 2019 at 06:15:28PM +0800, Ming Lei wrote: > 64K PAGE_SIZE is popular on ARM64 or other ARCHs, and 64K has been big > enough to break some devices probably, so change the logic to split bio > if the only bvec's length is > SZ_4K instead of PAGE_SIZE. I don't think this makes sense as-is given that blk_queue_max_hw_sectors, blk_queue_max_segment_size and co all check for a minimum of PAGE_SIZE and warn otherwise, and blk_bio_segment_split uses PAGE_SIZE for its short cut as well. So I don't think this has been a problem in practice, and if it was this patch is not enough. So either we leave things as is, or we need to do a real audit for code using PAGE_SIZE as the minimum I/O granularity and replace it everywhere a well as updating the documentation. Which might be a good thing given that variable sized limits are weird.