From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id D106C4CE0F for ; Mon, 12 Feb 2024 21:34:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707773702; cv=none; b=SS4S9tE8YaMoht59FtNQ725uKCa/mw+y9vMPI7d5izvEnEkIIDuX6x5d9gQ4Uww/735Z/Pt53vQ0m2W9j94idUzbKJ2W5EbH8wfSGPUuZ3iTlLIppq5SOfEwRTktRUHYpLUKFQNjL+VV6vTJj6F8oUPDjGXIeDc6iqMhjqgx7KA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707773702; c=relaxed/simple; bh=E1kWsqFDQhM/T3jJEBZxpbYuGRyEfIFfPycZCQEx3vs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=YYgQn2W4uSq4QX7bKdIjKS2e5bARXHPRprIt/HuTON2Fj7K8mOo0Si3FooMU9pcyp6MHtMT8wBp0jeR/h+5pSSK9x6DpL5Sr30IrQ8uosibX5Z2kceLb23MbvWi+49YB+GxVmm/dzezFAXodXZE1Z/h6LXZaHf0/8SARRVglfrE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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" Cc: linux-arm-kernel@lists.infradead.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org 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 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.