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 EB67DECE581 for ; Mon, 9 Sep 2024 23:16:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:Mime-Version:References:In-Reply-To:Message-Id:Subject:Cc:To: From:Date:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=tJY7hQfSgnpfFgsX1qQtt1Z4K47TIVxeyt/GZXza9eI=; b=SOcJpUMZEBtqIOAiv8ZLKTSWcO fQCCJaHzlwIxItQwM0e2xTYdzb7r5vLwERWgaPkqMJ437yWK2Pu6G00lZZIKkJ8NTJzkxwli+pqis HekhDt1B2GF09gitX0uoH2uVGrVreoUSFCNf+E5X6BpcPjnlR0oenJhf4xlVxTHefLXA+l6d5XRw3 P+M3DFOYqDK60o2A0tRJDlBs3LangoTDdT3OsAUlSQwvjOjgZ0Obv0bd52i8AH9Xg5drpE7Aw6Mdh prVtiXp7rGhxNdvDxzvpi+wdXla8l81IGCKArrVhXMdKmVKDLCoVsGm/Xbfl7khtzFjGPt+NAU26k LAPitF4Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1snnck-00000003YZm-3IUt; Mon, 09 Sep 2024 23:16:46 +0000 Received: from dfw.source.kernel.org ([2604:1380:4641:c500::1]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1snnbi-00000003YRJ-2LEJ for linux-arm-kernel@lists.infradead.org; Mon, 09 Sep 2024 23:15:44 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id 85B9A5C0206; Mon, 9 Sep 2024 23:15:37 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F378EC4CEC5; Mon, 9 Sep 2024 23:15:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1725923740; bh=luzSVNn4nvUpJ3QTHAb9p3Ik4ksmlSH5EahYohflukY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=xpK8zwiynZ0m10l28wwaoK+1o2zr4ZpU5iOoMkokRROxfrxRyELqVTZEUovGd/OEJ BgcTq+oRgsNSSWq7xyNkhCkJZ1n41LiFfwEJ40POx6cYmw5lXT7uh73qEtwdf4jqpC RuUgUXEA7PrIpIpQl8f40lD53HvGFdEUMWh3JpcI= Date: Mon, 9 Sep 2024 16:15:39 -0700 From: Andrew Morton To: Peter Xu Cc: Yan Zhao , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Gavin Shan , Catalin Marinas , x86@kernel.org, Ingo Molnar , Paolo Bonzini , Dave Hansen , Thomas Gleixner , Alistair Popple , kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Sean Christopherson , Oscar Salvador , Jason Gunthorpe , Borislav Petkov , Zi Yan , Axel Rasmussen , David Hildenbrand , Will Deacon , Kefeng Wang , Alex Williamson Subject: Re: [PATCH v2 07/19] mm/fork: Accept huge pfnmap entries Message-Id: <20240909161539.aa685e3eb44cdc786b8c05d2@linux-foundation.org> In-Reply-To: References: <20240826204353.2228736-1-peterx@redhat.com> <20240826204353.2228736-8-peterx@redhat.com> <20240909152546.4ef47308e560ce120156bc35@linux-foundation.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240909_161542_754197_6B654958 X-CRM114-Status: GOOD ( 28.65 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, 9 Sep 2024 18:43:22 -0400 Peter Xu wrote: > > > > Do we need the logic to clear dirty bit in the child as that in > > > > __copy_present_ptes()? (and also for the pmd's case). > > > > > > > > e.g. > > > > if (vma->vm_flags & VM_SHARED) > > > > pud = pud_mkclean(pud); > > > > > > Yeah, good question. I remember I thought about that when initially > > > working on these lines, but I forgot the details, or maybe I simply tried > > > to stick with the current code base, as the dirty bit used to be kept even > > > in the child here. > > > > > > I'd expect there's only performance differences, but still sounds like I'd > > > better leave that to whoever knows the best on the implications, then draft > > > it as a separate patch but only when needed. > > > > Sorry, but this vaguensss simply leaves me with nowhere to go. > > > > I'll drop the series - let's revisit after -rc1 please. > > Andrew, would you please explain why it needs to be dropped? > > I meant in the reply that I think we should leave that as is, and I think > so far nobody in real life should care much on this bit, so I think it's > fine to leave the dirty bit as-is. > > I still think whoever has a better use of the dirty bit and would like to > change the behavior should find the use case and work on top, but only if > necessary. Well. "I'd expect there's only performance differences" means to me "there might be correctness issues, I don't know". Is it or is it not merely a performance thing?