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Date: Sat, 25 Apr 2020 20:01:24 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: Anshuman Khandual <anshuman.khandual@....com> 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 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.
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