From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.223.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8E2123C1F22 for ; Fri, 15 May 2026 14:52:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=195.135.223.131 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778856725; cv=none; b=Tm+1DBe3bbvyKwiupwq1cSYiKxzpjKztuzVsUB9gi0BLSFNfTDOjP03mvHWMtpsJJVB41JiTYesdXxeyL39eQB0xCGIAmwjdfOEZfvuLTD91RyrcCUDnjj+iEXmMMLuqdE5+7EPU8I1J289m0h2bv3wmfD4dMD2lch6CjBHikNk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778856725; c=relaxed/simple; bh=/+b/V5bDHHWru7Bz5kIaZTKrsXrjFN3haRDJFBMCoeU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=TYs2T/Rbay7xLNpmnISU76LQXbNSbNxZrlP+fyr1Puz0B/OgGwyuwQRVGXvAIxF3cbrQ334L1iqrIShA1ZXJ2VWvia7nm1o3sHteRLe0dkTResoQGjCLmnuG2rmPMp1E8YoN+LYeUgo7PenzsQybxsyH0gVMn553sR9pzh5hNpA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz; spf=pass smtp.mailfrom=suse.cz; arc=none smtp.client-ip=195.135.223.131 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.cz Received: from imap1.dmz-prg2.suse.org (imap1.dmz-prg2.suse.org [IPv6:2a07:de40:b281:104:10:150:64:97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 4B04666D5C; Fri, 15 May 2026 14:52:00 +0000 (UTC) Authentication-Results: smtp-out2.suse.de; none Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 041E0593A9; Fri, 15 May 2026 14:52:00 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id BdG/ABAzB2onPgAAD6G6ig (envelope-from ); Fri, 15 May 2026 14:52:00 +0000 Date: Fri, 15 May 2026 16:51:58 +0200 From: David Sterba To: "H. Peter Anvin" Cc: kreijack@inwind.it, Goffredo Baroncelli , Christoph Hellwig , Andrew Morton , Catalin Marinas , Will Deacon , Ard Biesheuvel , Huacai Chen , WANG Xuerui , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , "Christophe Leroy (CS GROUP)" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Herbert Xu , Dan Williams , Chris Mason , David Sterba , Arnd Bergmann , Song Liu , Yu Kuai , Li Nan , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-crypto@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-arch@vger.kernel.org, linux-raid@vger.kernel.org Subject: Re: [PATCH 01/19] btrfs: require at least 4 devices for RAID 6 Message-ID: <20260515145158.GP2558453@suse.cz> Reply-To: dsterba@suse.cz References: <20260512052230.2947683-1-hch@lst.de> <20260512052230.2947683-2-hch@lst.de> <20260512114231.GG2558453@suse.cz> <20260513054742.GA1018@lst.de> <0a8d1ff4-f5a2-49e9-aa45-d25dbe4ded40@libero.it> <0507CCEF-0548-442F-8703-1D006B5E068B@zytor.com> Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <0507CCEF-0548-442F-8703-1D006B5E068B@zytor.com> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) X-Rspamd-Pre-Result: action=no action; module=replies; Message is reply to one we originated X-Spamd-Result: default: False [-4.00 / 50.00]; REPLY(-4.00)[] X-Rspamd-Queue-Id: 4B04666D5C X-Spam-Score: -4.00 X-Rspamd-Pre-Result: action=no action; module=replies; Message is reply to one we originated X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Action: no action X-Spam-Flag: NO X-Spam-Level: On Thu, May 14, 2026 at 12:57:53PM -0700, H. Peter Anvin wrote: > On May 14, 2026 12:51:59 PM PDT, Goffredo Baroncelli wrote: > >On 13/05/2026 07.47, Christoph Hellwig wrote: > >> On Tue, May 12, 2026 at 01:42:31PM +0200, David Sterba wrote: > > > >> > >>> The degenerate modes of > >>> raid0, 5, or 6 are explicit as a possible middle step when converting > >>> profiles. We can use a fallback implementation for this case if the > >>> accelerated implementations cannot do it. > >> > >> This is not about a degenerated mode. For a degenerated RAID 6, parity > >> generation uses the RAID 5 XOR routines as the second parity will be > >> missing. This is about generating two parities for a single data disk, > >> which must be explicitly selected. > >> > > > >I think that the David concern is : "what happens for an already > >existing btrfs raid6 3 disks filesystem when the user upgrade the kernel ?" > >(I am thinking when a new BG needs to be allocated)... > > That's what I'm saying – it should invoke the RAID-1 code under the cover (as with 3 disks, D = P = Q.) Thanks, it was not clear to me what you meant. For the two edge cases the code should do simple memcpy for both calculations of parity and recovery. 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 561C9CD4F25 for ; Fri, 15 May 2026 14:52:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:Reply-To:List-Subscribe:List-Help: List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=RQhhHr5amBq+8YNxVaxPU6v9tukgMDWBmcSLRDmt1IY=; b=E02x0sx1rAe6I/ emHI8FQjdWK9DaOjeanpsHdF5la0X6XnRCr9vut0MwVlN3wq8dyAr1YhO28wbPoB9kbJ+0F5eTuBU 0WyTQID3GRrfnGpo6Qr0sklXblwySULwZJBkFklelIABPOq0aWnJtY6HA+mrbBBcVbj4rbLrFQ7QS xcgwdeAbvlVjmEUq+V1BPcYKA0XyZNDRJWmNctcuy9NaDdyUgOD5Vl2VHuOhp0JxS2nM/O+7F6OFK 0kis52z5erbs17maTlYKGhmfXuwCGb/WQhiPesMnpqYYOf3zfbZrAQdR8FRW8yjXRVFQI7cTlQ9PO B/VJXuk2llYTcZPyPZlg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wNttX-00000008cgz-0DZ0; Fri, 15 May 2026 14:52:07 +0000 Received: from desiato.infradead.org ([2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wNttV-00000008cge-1G9S for linux-riscv@bombadil.infradead.org; Fri, 15 May 2026 14:52:05 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Reply-To:Message-ID:Subject:Cc:To:From: Date:Sender:Content-ID:Content-Description; bh=C1D/1YterPCnTmcPwmatqIt56Q+poHbCW9oYvcHSQ2M=; b=JvkmrGozrQD/Wz7M2hi5DuoPAQ 9h1oBzlufBFLXcNakM+2o+rzgELLmNOo/aDUg+79sDqlWkqGsfRu5m2xmZZ1rT6PlAzux+nHZVt3f CHUasugkPnulQ8tCAV/N/04mFQg4hOssjnnj7vBmZAo9k8LQfo25rKDyppgl3cMlkM0ImCo9x9D0C 9vBV+Ju/yWOvP/KTpCYcl0TQw2Yi4MUq3dCbUilKCZ7rZ+jTDBr91pgvgLA56UR8rb2lRCkvaxFxI LN81DT0MtPDj8ivdm1WO1qbP8Vf8ezlzrTqfHc38Tb43PYc6XKPIM7DUZgMJFszfee4l9pN1AntPd /Bw4NIVg==; Received: from smtp-out2.suse.de ([2a07:de40:b251:101:10:150:64:2]) by desiato.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wNttS-00000005V0Y-0IRs for linux-riscv@lists.infradead.org; Fri, 15 May 2026 14:52:04 +0000 Received: from imap1.dmz-prg2.suse.org (imap1.dmz-prg2.suse.org [IPv6:2a07:de40:b281:104:10:150:64:97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 4B04666D5C; Fri, 15 May 2026 14:52:00 +0000 (UTC) Authentication-Results: smtp-out2.suse.de; none Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 041E0593A9; Fri, 15 May 2026 14:52:00 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id BdG/ABAzB2onPgAAD6G6ig (envelope-from ); Fri, 15 May 2026 14:52:00 +0000 Date: Fri, 15 May 2026 16:51:58 +0200 From: David Sterba To: "H. Peter Anvin" Cc: kreijack@inwind.it, Goffredo Baroncelli , Christoph Hellwig , Andrew Morton , Catalin Marinas , Will Deacon , Ard Biesheuvel , Huacai Chen , WANG Xuerui , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , "Christophe Leroy (CS GROUP)" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Herbert Xu , Dan Williams , Chris Mason , David Sterba , Arnd Bergmann , Song Liu , Yu Kuai , Li Nan , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-crypto@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-arch@vger.kernel.org, linux-raid@vger.kernel.org Subject: Re: [PATCH 01/19] btrfs: require at least 4 devices for RAID 6 Message-ID: <20260515145158.GP2558453@suse.cz> References: <20260512052230.2947683-1-hch@lst.de> <20260512052230.2947683-2-hch@lst.de> <20260512114231.GG2558453@suse.cz> <20260513054742.GA1018@lst.de> <0a8d1ff4-f5a2-49e9-aa45-d25dbe4ded40@libero.it> <0507CCEF-0548-442F-8703-1D006B5E068B@zytor.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <0507CCEF-0548-442F-8703-1D006B5E068B@zytor.com> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) X-Rspamd-Pre-Result: action=no action; module=replies; Message is reply to one we originated X-Spamd-Result: default: False [-4.00 / 50.00]; REPLY(-4.00)[] X-Rspamd-Queue-Id: 4B04666D5C X-Rspamd-Pre-Result: action=no action; module=replies; Message is reply to one we originated X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Action: no action X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260515_155202_533372_D0D3E01E X-CRM114-Status: GOOD ( 21.62 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: dsterba@suse.cz Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org T24gVGh1LCBNYXkgMTQsIDIwMjYgYXQgMTI6NTc6NTNQTSAtMDcwMCwgSC4gUGV0ZXIgQW52aW4g d3JvdGU6Cj4gT24gTWF5IDE0LCAyMDI2IDEyOjUxOjU5IFBNIFBEVCwgR29mZnJlZG8gQmFyb25j ZWxsaSA8a3JlaWphY2tAbGliZXJvLml0PiB3cm90ZToKPiA+T24gMTMvMDUvMjAyNiAwNy40Nywg Q2hyaXN0b3BoIEhlbGx3aWcgd3JvdGU6Cj4gPj4gT24gVHVlLCBNYXkgMTIsIDIwMjYgYXQgMDE6 NDI6MzFQTSArMDIwMCwgRGF2aWQgU3RlcmJhIHdyb3RlOgo+ID4KPiA+PiAKPiA+Pj4gVGhlIGRl Z2VuZXJhdGUgbW9kZXMgb2YKPiA+Pj4gcmFpZDAsIDUsIG9yIDYgYXJlIGV4cGxpY2l0IGFzIGEg cG9zc2libGUgbWlkZGxlIHN0ZXAgd2hlbiBjb252ZXJ0aW5nCj4gPj4+IHByb2ZpbGVzLiAgV2Ug Y2FuIHVzZSBhIGZhbGxiYWNrIGltcGxlbWVudGF0aW9uIGZvciB0aGlzIGNhc2UgaWYgdGhlCj4g Pj4+IGFjY2VsZXJhdGVkIGltcGxlbWVudGF0aW9ucyBjYW5ub3QgZG8gaXQuCj4gPj4gCj4gPj4g VGhpcyBpcyBub3QgYWJvdXQgYSBkZWdlbmVyYXRlZCBtb2RlLiAgRm9yIGEgZGVnZW5lcmF0ZWQg UkFJRCA2LCBwYXJpdHkKPiA+PiBnZW5lcmF0aW9uIHVzZXMgdGhlIFJBSUQgNSBYT1Igcm91dGlu ZXMgYXMgdGhlIHNlY29uZCBwYXJpdHkgd2lsbCBiZQo+ID4+IG1pc3NpbmcuICBUaGlzIGlzIGFi b3V0IGdlbmVyYXRpbmcgdHdvIHBhcml0aWVzIGZvciBhIHNpbmdsZSBkYXRhIGRpc2ssCj4gPj4g d2hpY2ggbXVzdCBiZSBleHBsaWNpdGx5IHNlbGVjdGVkLgo+ID4+IAo+ID4KPiA+SSB0aGluayB0 aGF0IHRoZSBEYXZpZCBjb25jZXJuIGlzIDogIndoYXQgaGFwcGVucyBmb3IgYW4gYWxyZWFkeQo+ ID5leGlzdGluZyBidHJmcyByYWlkNiAzIGRpc2tzIGZpbGVzeXN0ZW0gd2hlbiB0aGUgdXNlciB1 cGdyYWRlIHRoZSBrZXJuZWwgPyIKPiA+KEkgYW0gdGhpbmtpbmcgd2hlbiBhIG5ldyBCRyBuZWVk cyB0byBiZSBhbGxvY2F0ZWQpLi4uCj4gCj4gVGhhdCdzIHdoYXQgSSdtIHNheWluZyDigJMgaXQg c2hvdWxkIGludm9rZSB0aGUgUkFJRC0xIGNvZGUgdW5kZXIgdGhlIGNvdmVyIChhcyB3aXRoIDMg ZGlza3MsIEQgPSBQID0gUS4pCgpUaGFua3MsIGl0IHdhcyBub3QgY2xlYXIgdG8gbWUgd2hhdCB5 b3UgbWVhbnQuIEZvciB0aGUgdHdvIGVkZ2UgY2FzZXMKdGhlIGNvZGUgc2hvdWxkIGRvIHNpbXBs ZSBtZW1jcHkgZm9yIGJvdGggY2FsY3VsYXRpb25zIG9mIHBhcml0eSBhbmQKcmVjb3ZlcnkuCgpf X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fXwpsaW51eC1yaXNj diBtYWlsaW5nIGxpc3QKbGludXgtcmlzY3ZAbGlzdHMuaW5mcmFkZWFkLm9yZwpodHRwOi8vbGlz dHMuaW5mcmFkZWFkLm9yZy9tYWlsbWFuL2xpc3RpbmZvL2xpbnV4LXJpc2N2Cg==