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 A0DFBC43441 for ; Wed, 21 Nov 2018 08:46:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 69DC220989 for ; Wed, 21 Nov 2018 08:46:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 69DC220989 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-btrfs-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728301AbeKUTTs (ORCPT ); Wed, 21 Nov 2018 14:19:48 -0500 Received: from verein.lst.de ([213.95.11.211]:50061 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728210AbeKUTTr (ORCPT ); Wed, 21 Nov 2018 14:19:47 -0500 Received: by newverein.lst.de (Postfix, from userid 2407) id 4F0CA68C19; Wed, 21 Nov 2018 09:46:08 +0100 (CET) Date: Wed, 21 Nov 2018 09:46:08 +0100 From: Christoph Hellwig To: Sagi Grimberg Cc: Ming Lei , Christoph Hellwig , Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Dave Chinner , Kent Overstreet , Mike Snitzer , dm-devel@redhat.com, Alexander Viro , linux-fsdevel@vger.kernel.org, Shaohua Li , linux-raid@vger.kernel.org, linux-erofs@lists.ozlabs.org, David Sterba , linux-btrfs@vger.kernel.org, "Darrick J . Wong" , linux-xfs@vger.kernel.org, Gao Xiang , Theodore Ts'o , linux-ext4@vger.kernel.org, Coly Li , linux-bcache@vger.kernel.org, Boaz Harrosh , Bob Peterson , cluster-devel@redhat.com Subject: Re: [PATCH V10 09/19] block: introduce bio_bvecs() Message-ID: <20181121084608.GA29622@lst.de> References: <002fe56b-25e4-573e-c09b-bb12c3e8d25a@grimberg.me> <20181120161651.GB2629@lst.de> <53526aae-fb9b-ee38-0a01-e5899e2d4e4d@grimberg.me> <20181121005902.GA31748@ming.t460p> <2d9bee7a-f010-dcf4-1184-094101058584@grimberg.me> <20181121034415.GA8408@ming.t460p> <2a47d336-c19b-6bf4-c247-d7382871eeea@grimberg.me> <7378bf49-5a7e-5622-d4d1-808ba37ce656@grimberg.me> <20181121050359.GA31915@ming.t460p> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Tue, Nov 20, 2018 at 09:35:07PM -0800, Sagi Grimberg wrote: >> Given it is over TCP, I guess it should be doable for you to preallocate one >> 256-bvec table in one page for each request, then sets the max segment size as >> (unsigned int)-1, and max segment number as 256, the preallocated table >> should work anytime. > > 256 bvec table is really a lot to preallocate, especially when its not > needed, I can easily initialize the bvec_iter on the bio bvec. If this > involves preallocation of the worst-case than I don't consider this to > be an improvement. Ok, I took a look at the nvme-tcp code and it seems you care about bios because you want a contiguos bio chunk for sending it down the networking code. Yes, in that case we sort of need to iterate over bios. But you already have a special case for discard, so you don't really need any of the magic in the bio_bvecs() helper either can can just count bi_vcnt in the bio.