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=-5.3 required=3.0 tests=BAYES_00, 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 D6F45C47095 for ; Mon, 7 Jun 2021 12:08:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C1BA861245 for ; Mon, 7 Jun 2021 12:08:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230319AbhFGMKR (ORCPT ); Mon, 7 Jun 2021 08:10:17 -0400 Received: from verein.lst.de ([213.95.11.211]:45916 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230286AbhFGMKR (ORCPT ); Mon, 7 Jun 2021 08:10:17 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 4CCDE67373; Mon, 7 Jun 2021 14:08:22 +0200 (CEST) Date: Mon, 7 Jun 2021 14:08:22 +0200 From: Christoph Hellwig To: Coly Li Cc: Christoph Hellwig , axboe@kernel.dk, linux-bcache@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Alexander Ullrich , Diego Ercolani , Jan Szubiak , Marco Rebhan , Matthias Ferdinand , Victor Westerhuis , Vojtech Pavlik , Rolf Fokkens , Thorsten Knabe , stable@vger.kernel.org, Kent Overstreet , Nix , Takashi Iwai Subject: Re: [PATCH v5 2/2] bcache: avoid oversized read request in cache missing code path Message-ID: <20210607120822.GA11665@lst.de> References: <20210607103539.12823-1-colyli@suse.de> <20210607103539.12823-3-colyli@suse.de> <20210607110657.GB6729@lst.de> <6d08d23b-b778-4e5f-a5f3-7106a42e26a1@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <6d08d23b-b778-4e5f-a5f3-7106a42e26a1@suse.de> User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Mon, Jun 07, 2021 at 07:55:22PM +0800, Coly Li wrote: > On 6/7/21 7:06 PM, Christoph Hellwig wrote: > > On Mon, Jun 07, 2021 at 06:35:39PM +0800, Coly Li wrote: > >> + /* Limitation for valid replace key size and cache_bio bvecs number */ > >> + size_limit = min_t(unsigned int, bio_max_segs(UINT_MAX) * PAGE_SECTORS, > >> + (1 << KEY_SIZE_BITS) - 1); > > bio_max_segs kaps the argument to BIO_MAX_VECS, so you might as well > > It was suggested to not directly access BIO_MAX_VECS by you, maybe I > misunderstood you. Yes, drivers really should not care about it. But hiding that behind a tiny wrapper doesn't help either. > > directly write BIO_MAX_VECS. Can you explain the PAGE_SECTORS here a bit > > more? Does this code path use discontiguous per-sector allocations? > > Preferably in a comment. > > > It is just because bch_bio_map() assume the maximum bio size is 1MB. It > was not true since the multiple pages bvecs > was merged in mainline kernel. >   > The PAGE_SECTORS part is legacy for 1MB maximum size bio (256*4KB), it > should be fixed/improved later to > use multiple pages for bio size > 1MB and replace bch_bio_map(). bch_bio_map and bch_bio_alloc_pages that poke directly into the bio are the root cause of a lot of these problems. I had a series fixing some of that but Kent did not like it. Drivers must not diretly access bi_vcnt or directly build bios. > Not any more. Now the line limit is 100 characters. Though I still > prefer 80 characters, place 86 characters in single line > makes the change more obvious. It makes it really hard to read in a normal terminal.