linux-kernel - Re: [PATCH 3/3] mm/hugetlb: Introduce HAVE_ARCH_CLEAR_HUGEPAGE

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Date:   Tue, 5 May 2020 08:21:34 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Helge Deller <deller@....de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Mike Kravetz <mike.kravetz@...cle.com>, x86@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        sparclinux@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] mm/hugetlb: Introduce HAVE_ARCH_CLEAR_HUGEPAGE_FLAGS



On 04/26/2020 08:31 AM, Andrew Morton wrote:
> On Sun, 26 Apr 2020 08:13:17 +0530 Anshuman Khandual <anshuman.khandual@....com> wrote:
> 
>>
>>
>> On 04/26/2020 06:25 AM, Andrew Morton wrote:
>>> On Tue, 14 Apr 2020 17:14:30 +0530 Anshuman Khandual <anshuman.khandual@....com> wrote:
>>>
>>>> There are multiple similar definitions for arch_clear_hugepage_flags() on
>>>> various platforms. This introduces HAVE_ARCH_CLEAR_HUGEPAGE_FLAGS for those
>>>> platforms that need to define their own arch_clear_hugepage_flags() while
>>>> also providing a generic fallback definition for others to use. This help
>>>> reduce code duplication.
>>>>
>>>> ...
>>>>
>>>> --- a/include/linux/hugetlb.h
>>>> +++ b/include/linux/hugetlb.h
>>>> @@ -544,6 +544,10 @@ static inline int is_hugepage_only_range(struct mm_struct *mm,
>>>>  }
>>>>  #endif
>>>>  
>>>> +#ifndef HAVE_ARCH_CLEAR_HUGEPAGE_FLAGS
>>>> +static inline void arch_clear_hugepage_flags(struct page *page) { }
>>>> +#endif
>>>> +
>>>>  #ifndef arch_make_huge_pte
>>>>  static inline pte_t arch_make_huge_pte(pte_t entry, struct vm_area_struct *vma,
>>>>  				       struct page *page, int writable)
>>>
>>> This is the rather old-school way of doing it.  The Linus-suggested way is
>>>
>>> #ifndef arch_clear_hugepage_flags
>>> static inline void arch_clear_hugepage_flags(struct page *page)
>>> {
>>> }
>>> #define arch_clear_hugepage_flags arch_clear_hugepage_flags
>>
>> Do we need that above line here ? Is not that implicit.
> 
> It depends if other header files want to test whether
> arch_clear_hugepage_flags is already defined.  If the header heorarchy
> is well-defined and working properly, they shouldn't need to, because
> we're reliably indluding the relevant arch header before (or early
> within) include/linux/hugetlb.h.
> 
> It would be nice if
> 
> #define arch_clear_hugepage_flags arch_clear_hugepage_flags
> #define arch_clear_hugepage_flags arch_clear_hugepage_flags
> 
> were to generate an compiler error but it doesn't.  If it did we could
> detect these incorrect inclusion orders.
> 
>>> #endif
>>>
>>> And the various arch headers do
>>>
>>> static inline void arch_clear_hugepage_flags(struct page *page)
>>> {
>>> 	<some implementation>
>>> }
>>> #define arch_clear_hugepage_flags arch_clear_hugepage_flags
>>>
>>> It's a small difference - mainly to avoid adding two variables to the
>>> overall namespace where one would do.
>>
>> Understood, will change and resend.
> 
> That's OK - I've queued up that fix.
>

Hello Andrew,

I might not have searched all the relevant trees or might have just searched
earlier than required. But I dont see these patches (or your proposed fixes)
either in mmotm (2020-04-29-23-04) or in next-20200504. Wondering if you are
waiting on a V2 for this series accommodating the changes you had proposed.

- Anshuman