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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (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 40F62C4829E for ; Mon, 12 Feb 2024 21:35:58 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4TYd706l3Mz3vXp for ; Tue, 13 Feb 2024 08:35:56 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=arm.com (client-ip=217.140.110.172; helo=foss.arm.com; envelope-from=ryan.roberts@arm.com; receiver=lists.ozlabs.org) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lists.ozlabs.org (Postfix) with ESMTP id 4TYd6W6Td1z3bZ1 for ; Tue, 13 Feb 2024 08:35:30 +1100 (AEDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id EE8BEDA7; Mon, 12 Feb 2024 13:35:39 -0800 (PST) Received: from [10.57.78.115] (unknown [10.57.78.115]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CF5003F766; Mon, 12 Feb 2024 13:34:54 -0800 (PST) Message-ID: <3bc05163-2671-4239-ae5a-b9207fdca459@arm.com> Date: Mon, 12 Feb 2024 21:34:53 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 03/25] mm: Make pte_next_pfn() a wrapper around pte_advance_pfn() Content-Language: en-GB To: David Hildenbrand , Catalin Marinas , Will Deacon , Ard Biesheuvel , Marc Zyngier , James Morse , Andrey Ryabinin , Andrew Morton , Matthew Wilcox , Mark Rutland , Kefeng Wang , John Hubbard , Zi Yan , Barry Song <21cnbao@gmail.com>, Alistair Popple , Yang Shi , Nicholas Piggin , Christophe Leroy , "Aneesh Kumar K.V" , "Naveen N. Rao" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" References: <20240202080756.1453939-1-ryan.roberts@arm.com> <20240202080756.1453939-4-ryan.roberts@arm.com> <828d2573-b5fe-43b3-b955-944c05bcdb60@redhat.com> From: Ryan Roberts In-Reply-To: <828d2573-b5fe-43b3-b955-944c05bcdb60@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-mm@kvack.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 12/02/2024 14:29, David Hildenbrand wrote: > On 12.02.24 15:10, Ryan Roberts wrote: >> On 12/02/2024 12:14, David Hildenbrand wrote: >>> On 02.02.24 09:07, Ryan Roberts wrote: >>>> The goal is to be able to advance a PTE by an arbitrary number of PFNs. >>>> So introduce a new API that takes a nr param. >>>> >>>> We are going to remove pte_next_pfn() and replace it with >>>> pte_advance_pfn(). As a first step, implement pte_next_pfn() as a >>>> wrapper around pte_advance_pfn() so that we can incrementally switch the >>>> architectures over. Once all arches are moved over, we will change all >>>> the core-mm callers to call pte_advance_pfn() directly and remove the >>>> wrapper. >>>> >>>> Signed-off-by: Ryan Roberts >>>> --- >>>>    include/linux/pgtable.h | 8 +++++++- >>>>    1 file changed, 7 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h >>>> index 5e7eaf8f2b97..815d92dcb96b 100644 >>>> --- a/include/linux/pgtable.h >>>> +++ b/include/linux/pgtable.h >>>> @@ -214,9 +214,15 @@ static inline int pmd_dirty(pmd_t pmd) >>>>        #ifndef pte_next_pfn >>>> +#ifndef pte_advance_pfn >>>> +static inline pte_t pte_advance_pfn(pte_t pte, unsigned long nr) >>>> +{ >>>> +    return __pte(pte_val(pte) + (nr << PFN_PTE_SHIFT)); >>>> +} >>>> +#endif >>>>    static inline pte_t pte_next_pfn(pte_t pte) >>>>    { >>>> -    return __pte(pte_val(pte) + (1UL << PFN_PTE_SHIFT)); >>>> +    return pte_advance_pfn(pte, 1); >>>>    } >>>>    #endif >>>>    >>> >>> I do wonder if we simply want to leave pte_next_pfn() around? Especially patch >>> #4, #6 don't really benefit from the change? So are the other set_ptes() >>> implementations. >>> >>> That is, only convert all pte_next_pfn()->pte_advance_pfn(), and leave a >>> pte_next_pfn() macro in place. >>> >>> Any downsides to that? >> >> The downside is just having multiple functions that effectively do the same >> thing. Personally I think its cleaner and easier to understand the code with >> just one generic function which we pass 1 to it where we only want to advance by >> 1. In the end, there are only a couple of places where pte_advance_pfn(1) is >> used, so doesn't really seem valuable to me to maintain a specialization. > > Well, not really functions, just a macro. Like we have set_pte_at() translating > to set_ptes(). > > Arguably, we have more callers of set_pte_at(). > > "Easier to understand", I don't know. :) > >> >> Unless you feel strongly that we need to keep pte_next_pfn() then I'd prefer to >> leave it as I've done in this series. > > Well, it makes you patch set shorter and there is less code churn. > > So personally, I'd just leave pte_next_pfn() in there. But whatever you prefer, > not the end of the world. I thought about this a bit more and remembered that I'm the apprentice so I've changed it as you suggested.