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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 150A8C43217 for ; Fri, 19 Nov 2021 16:12:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EB7D761B1E for ; Fri, 19 Nov 2021 16:12:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236279AbhKSQP2 (ORCPT ); Fri, 19 Nov 2021 11:15:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55022 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231173AbhKSQP1 (ORCPT ); Fri, 19 Nov 2021 11:15:27 -0500 Received: from mail-wr1-x436.google.com (mail-wr1-x436.google.com [IPv6:2a00:1450:4864:20::436]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7E675C061574; Fri, 19 Nov 2021 08:12:24 -0800 (PST) Received: by mail-wr1-x436.google.com with SMTP id b12so18998966wrh.4; Fri, 19 Nov 2021 08:12:24 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=message-id:date:mime-version:user-agent:subject:content-language:to :cc:references:from:in-reply-to:content-transfer-encoding; bh=ugr1swvvEJM7P07dTrUMW86aHmgr9RVOKFoLL2kQN7k=; b=lFlyvkBNI61mJyUJLQ1+hcFZu152Rj5qZK9mAkDP6bOJesLhBEd3Q4Oq83qIYEd64n YITNPwkZi9S7IB6Inh60GB/VEkSv28veKOaIGDMIPbCKTFzqAkbspPLR28oVvo5U5vKX ni4AocUEsv6MI6QlC5aDBhUxTPYJ6WUDtSoDVTmcNAcrcrW+S1gPrCGf3ON0VZfJ6JKa 0KBtAUbroY6eHDRyQJdN136bKjpeWs281Zu15Ruh/5ySpQ1d5ekmM8Ta6jagf5CN7g3S kwp92bvu9VLsql4q4anafWvPndH2TGTUpGf0qg8qKM1C7v1a4tqdU9+hNI70/o/Awrbu 5GRw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=ugr1swvvEJM7P07dTrUMW86aHmgr9RVOKFoLL2kQN7k=; b=BYrdkGvg6wiyPzrnDBhUSphzMAL5umH7l/E2xiClgXhdh4CZbWrfDVAZ3jgh3mLeUP 7Xgvrlsi9aaCvY+NfzHTLmThyXiY/EVxSPc0DZX7Rilxgxp7Xy0ssCTyOoTxkfoBEhJs BaglXTwlLginJdbqCnaa66rAGBebOvW3fq8zOwFYb3HG9hVQDB0F1+dRx7PeMizMjyOm UA/YG7F/EAo/QYQwuRX0mKc6AYWCHLDf+7LgBobeYSZGJxcy1yyY8EdoXtwn0P6bo5It h6oZNUSkqwE8o/u0463Z2RfQz/izwfJT+sDudCOKxFnXD8QbDE27xD1QjB+WeQxnjD81 sGww== X-Gm-Message-State: AOAM531wyMlsO4fH7FjJum5k9sa4d7hLmoxDsc/NBdxtrjjdg01YR3gX g7VQBKJkwVhEGp7du7gUENw= X-Google-Smtp-Source: ABdhPJxXT53cxKGwOTawEJZsAHGDZX4/cS9uLMXoPT1yRB0yOWFLwaopD6E8urQvNF7W4NC52G5yJw== X-Received: by 2002:a05:6000:156a:: with SMTP id 10mr8724643wrz.87.1637338343047; Fri, 19 Nov 2021 08:12:23 -0800 (PST) Received: from [192.168.0.160] ([170.253.36.171]) by smtp.gmail.com with ESMTPSA id a1sm191231wri.89.2021.11.19.08.12.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 19 Nov 2021 08:12:22 -0800 (PST) Message-ID: Date: Fri, 19 Nov 2021 17:12:19 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.0 Subject: Re: [PATCH 00/17] Add memberof(), split some headers, and slightly simplify code Content-Language: en-US To: Arnd Bergmann Cc: LKML , Ajit Khaparde , Andrew Morton , Andy Shevchenko , Bjorn Andersson , Borislav Petkov , Corey Minyard , Chris Mason , Christian Brauner , David Sterba , Jani Nikula , Jason Wang , Jitendra Bhivare , John Hubbard , "John S . Gruber" , Jonathan Cameron , Joonas Lahtinen , Josef Bacik , Kees Cook , Ketan Mukadam , Len Brown , "Michael S. Tsirkin" , Miguel Ojeda , Mike Rapoport , Nick Desaulniers , "Rafael J. Wysocki" , Rasmus Villemoes , Rodrigo Vivi , Russell King , Somnath Kotur , Sriharsha Basavapatna , Subbu Seetharaman , Intel Graphics , ACPI Devel Maling List , Linux ARM , linux-btrfs , linux-scsi , Networking , "open list:DRM DRIVER FOR QEMU'S CIRRUS DEVICE" References: <20211119113644.1600-1-alx.manpages@gmail.com> <434296d3-8fe1-f1d2-ee9d-ea25d6c4e43e@gmail.com> From: "Alejandro Colomar (man-pages)" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Arnd, On 11/19/21 16:57, Arnd Bergmann wrote: > > From what I can tell, linux/stddef.h is tiny, I don't think it's really > worth optimizing this part. I have spent some time last year > trying to untangle some of the more interesting headers, but ended > up not completing this as there are some really hard problems > once you start getting to the interesting bits. In this case it was not about being worth it or not, but that the fact that adding memberof() would break, unless I use 0 instead of NULL for the implementation of memberof(), which I'm against, or I split stddef. If I don't do either of those, I'm creating a circular dependency, and it doesn't compile. > > The approach I tried was roughly: > > - For each header in the kernel, create a preprocessed version > that includes all the indirect includes, from that start a set > of lookup tables that record which header is eventually included > by which ones, and the size of each preprocessed header in > bytes > > - For a given kernel configuration (e.g. defconfig or allmodconfig) > that I'm most interested in, look at which files are built, and what > the direct includes are in the source files. > > - Sort the headers by the product of the number of direct includes > and the preprocessed size: the largest ones are those that are > worth looking at first. > > - use graphviz to visualize the directed graph showing the includes > between the top 100 headers in that list. You get something like > I had in [1], or the version afterwards at [2]. > > - split out unneeded indirect includes from the headers in the center > of that graph, typically by splitting out struct definitions. > > - repeat. > > The main problem with this approach is that as soon as you start > actually reducing the unneeded indirect includes, you end up with > countless .c files that no longer build because they are missing a > direct include for something that was always included somewhere > deep underneath, so I needed a second set of scripts to add > direct includes to every .c file. > > On the plus side, I did see something on the order of a 30% > compile speed improvement with clang, which is insane > given that this only removed dead definitions. Huh! I'd like to see the kernel some day not having _any_ hidden dependencies. For the moment, since my intent is familiarizing with kernel programming, and not necessarily improving performance considerably (at least not in the first rounds of changes), I prefer starting where it more directly affects what I initially intended to change in the kernel, which in this case was adding memberof(). > >> But I'll note that linux/fs.h, linux/sched.h, linux/mm.h are >> interesting headers for further splitting. >> >> >> BTW, I also have a longstanding doubt about >> how header files are organized in the kernel, >> and which headers can and cannot be included >> from which other files. >> >> For example I see that files in samples or scripts or tools, >> that redefine many things such as offsetof() or ARRAY_SIZE(), >> and I don't know if there's a good reason for that, >> or if I should simply remove all that stuff and >> include everywhere I see offsetof() being used. > > The main issue here is that user space code should not > include anything outside of include/uapi/ and arch/*/include/uapi/ Okay. That's good to know. So everything can use uapi code, and uapi code can only use uapi code, right? Every duplicate definition of something outside of uapi should/could be removed. > > offsetof() is defined in include/linux/stddef.h, so this is by > definition not accessible here. It appears that there is also > an include/uapi/linux/stddef.h that is really strange because > it includes linux/compiler_types.h, which in turn is outside > of uapi/. This should probably be fixed. I see. Then, perhaps it would be better to define offsetof() _only_ inside uapi/, and use that definition from everywhere else, and therefore remove the non-uapi version, right? Thanks, Alex -- Alejandro Colomar Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es/