linux-kernel - Re: [PATCH v1 2/8] powerpc: hugetlb: Convert set_huge_pte

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Date:   Fri, 22 Sep 2023 10:37:52 +0100
From:   Ryan Roberts <ryan.roberts@....com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Helge Deller <deller@....de>,
        Nicholas Piggin <npiggin@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        "David S. Miller" <davem@...emloft.net>,
        Arnd Bergmann <arnd@...db.de>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        SeongJae Park <sj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Peter Xu <peterx@...hat.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Qi Zheng <zhengqi.arch@...edance.com>
Cc:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v1 2/8] powerpc: hugetlb: Convert set_huge_pte_at() to
 take vma

On 22/09/2023 10:14, Christophe Leroy wrote:
> 
> 
> Le 22/09/2023 à 10:41, Ryan Roberts a écrit :
>> On 22/09/2023 09:10, Christophe Leroy wrote:
>>>
>>>
>>>> I'm happy to take your proposed approach if that's your preference. Another
>>>> option is to use a dummy VMA, as I have done in the core code, for the one call
>>>> site that calls set_huge_pte_at() with init_mm:
>>>>
>>>> struct vm_area_struct vma = TLB_FLUSH_VMA(&init_mm, 0);
>>>>
>>>> This is an existing macro that creates a dummy vma with vma->vm_mm filled in.
>>>> Then I pass &vma to the function.
>>>
>>> I don't like that, I prefer the solution I proposed. We already have a
>>> couple places where powerpc do things based on whether vma is NULL or not.
>>>
>>>>
>>>> Or yet another option would be to keep the mm param as is in set_huge_pte_at(),
>>>> and add a size param to the function. But then all call sites have the burden of
>>>> figuring out the size of the huge pte (although I think most know already).
>>>
>>> Indeed.
>>>
>>> arch_make_huge_pte() used to take a vma until commit 79c1c594f49a
>>> ("mm/hugetlb: change parameters of arch_make_huge_pte()").
>>>
>>> Should we try and have the same approach ? Or is it irrelevant ?
>>
>> See [1]; I'm going to rework to pass mm + size parameter since the current
>> approach will break riscv.
> 
> Can you pass a shift parameter instead of a size, like 
> arch_make_huge_pte() ? As far as I remember it is easier to handle a 
> shift than a size.

Most of the call sites already have the size, not the shift. And arm64 needs the
size, so it would have do (1UL << shift). So on that basis, I prefer to pass
size. huge_pte_clear() already passes long unsigned sz, so I'd rather follow
that pattern.

> 
> Christophe