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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 CED85C48BD1 for ; Thu, 10 Jun 2021 14:50:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B5DA46128A for ; Thu, 10 Jun 2021 14:50:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231511AbhFJOwU (ORCPT ); Thu, 10 Jun 2021 10:52:20 -0400 Received: from pegase1.c-s.fr ([93.17.236.30]:8321 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231336AbhFJOwQ (ORCPT ); Thu, 10 Jun 2021 10:52:16 -0400 Received: from localhost (mailhub3.si.c-s.fr [192.168.12.233]) by localhost (Postfix) with ESMTP id 4G16Mt6NybzBBTQ; Thu, 10 Jun 2021 16:50:18 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id IgLzEJiZ-597; Thu, 10 Jun 2021 16:50:18 +0200 (CEST) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 4G16Mt5QJzzBB9r; Thu, 10 Jun 2021 16:50:18 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 375368B81B; Thu, 10 Jun 2021 16:50:18 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id DzO9RJN6YzIB; Thu, 10 Jun 2021 16:50:18 +0200 (CEST) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id B07968B80F; Thu, 10 Jun 2021 16:50:17 +0200 (CEST) Subject: Re: [PATCH] btrfs: Disable BTRFS on platforms having 256K pages To: Chris Mason Cc: Josef Bacik , David Sterba , "linux-kernel@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , linux-btrfs , "linux-hexagon@vger.kernel.org" References: <185278AF-1D87-432D-87E9-C86B3223113E@fb.com> From: Christophe Leroy Message-ID: Date: Thu, 10 Jun 2021 16:50:09 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <185278AF-1D87-432D-87E9-C86B3223113E@fb.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 10/06/2021 à 15:54, Chris Mason a écrit : > >> On Jun 10, 2021, at 1:23 AM, Christophe Leroy wrote: >> >> With a config having PAGE_SIZE set to 256K, BTRFS build fails >> with the following message >> >> include/linux/compiler_types.h:326:38: error: call to '__compiletime_assert_791' declared with attribute error: BUILD_BUG_ON failed: (BTRFS_MAX_COMPRESSED % PAGE_SIZE) != 0 >> >> BTRFS_MAX_COMPRESSED being 128K, BTRFS cannot support platforms with >> 256K pages at the time being. >> >> There are two platforms that can select 256K pages: >> - hexagon >> - powerpc >> >> Disable BTRFS when 256K page size is selected. >> > > We’ll have other subpage blocksize concerns with 256K pages, but this BTRFS_MAX_COMPRESSED #define is arbitrary. It’s just trying to have an upper bound on the amount of memory we’ll need to uncompress a single page’s worth of random reads. > > We could change it to max(PAGE_SIZE, 128K) or just bump to 256K. > But if 256K is problematic in other ways, is it worth bumping BTRFS_MAX_COMPRESSED to 256K ? David, in below mail, said that 256K support would require deaper changes. So disabling BTRFS support seems the easiest solution for the time being, at least for Stable (I forgot the Fixes: tag and the CC: to stable). On powerpc, 256k pages is a corner case, it requires customised binutils, so I don't think disabling BTRFS is a issue there. For hexagon I don't know. https://lkml.org/lkml/2021/6/9/978 Le 09/06/2021 à 17:22, David Sterba a écrit : > On Wed, Jun 09, 2021 at 04:01:20PM +0200, Christophe Leroy wrote: >> Le 09/06/2021 à 15:55, kernel test robot a écrit : >>> tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master >>> head: 368094df48e680fa51cedb68537408cfa64b788e >>> commit: 4eeef098b43242ed145c83fba9989d586d707589 powerpc/44x: Remove STDBINUTILS kconfig option >>> date: 4 months ago >>> config: powerpc-randconfig-r012-20210609 (attached as .config) >>> compiler: powerpc-linux-gcc (GCC) 9.3.0 >> >> That's a BTRFS issue, and not directly linked to the above mentioned commit. Before that commit the >> problem was already present. >> >> Problem is that with 256k PAGE_SIZE, following BUILD_BUG() pops up: >> >> BUILD_BUG_ON((BTRFS_MAX_COMPRESSED % PAGE_SIZE) != 0) > > A 256K page is a problem for btrfs, until now I was not even aware > there's an architecture supporting that so. That the build fails is > probably best thing. Maximum metadata nodesize supported is 64K and > having that on a 256K page would need deeper changes, no top of the > currently developed subpage changes (that do 4K blocks on 64K pages). >