linux-kernel - Re: [PATCH 01/19] mm: Introduce ARCH_SUPPORTS_HUGE

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Message-ID: <def1dda5-a2e8-4f6b-85f6-1d6981ab0140@redhat.com>
Date: Fri, 9 Aug 2024 18:34:15 +0200
From: David Hildenbrand <david@...hat.com>
To: Peter Xu <peterx@...hat.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Cc: Sean Christopherson <seanjc@...gle.com>,
 Oscar Salvador <osalvador@...e.de>, Jason Gunthorpe <jgg@...dia.com>,
 Axel Rasmussen <axelrasmussen@...gle.com>,
 linux-arm-kernel@...ts.infradead.org, x86@...nel.org,
 Will Deacon <will@...nel.org>, Gavin Shan <gshan@...hat.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Zi Yan <ziy@...dia.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Catalin Marinas <catalin.marinas@....com>, Ingo Molnar <mingo@...hat.com>,
 Alistair Popple <apopple@...dia.com>, Borislav Petkov <bp@...en8.de>,
 Thomas Gleixner <tglx@...utronix.de>, kvm@...r.kernel.org,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 Alex Williamson <alex.williamson@...hat.com>, Yan Zhao <yan.y.zhao@...el.com>
Subject: Re: [PATCH 01/19] mm: Introduce ARCH_SUPPORTS_HUGE_PFNMAP and special
 bits to pmd/pud

On 09.08.24 18:08, Peter Xu wrote:
> This patch introduces the option to introduce special pte bit into
> pmd/puds.  Archs can start to define pmd_special / pud_special when
> supported by selecting the new option.  Per-arch support will be added
> later.
> 
> Before that, create fallbacks for these helpers so that they are always
> available.
> 
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>   include/linux/mm.h | 24 ++++++++++++++++++++++++
>   mm/Kconfig         | 13 +++++++++++++
>   2 files changed, 37 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 43b40334e9b2..90ca84200800 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2644,6 +2644,30 @@ static inline pte_t pte_mkspecial(pte_t pte)
>   }
>   #endif
>   
> +#ifndef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP
> +static inline bool pmd_special(pmd_t pmd)
> +{
> +	return false;
> +}
> +
> +static inline pmd_t pmd_mkspecial(pmd_t pmd)
> +{
> +	return pmd;
> +}
> +#endif	/* CONFIG_ARCH_SUPPORTS_PMD_PFNMAP */
> +
> +#ifndef CONFIG_ARCH_SUPPORTS_PUD_PFNMAP
> +static inline bool pud_special(pud_t pud)
> +{
> +	return false;
> +}
> +
> +static inline pud_t pud_mkspecial(pud_t pud)
> +{
> +	return pud;
> +}
> +#endif	/* CONFIG_ARCH_SUPPORTS_PUD_PFNMAP */
> +
>   #ifndef CONFIG_ARCH_HAS_PTE_DEVMAP
>   static inline int pte_devmap(pte_t pte)
>   {
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 3936fe4d26d9..3db0eebb53e2 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -881,6 +881,19 @@ endif # TRANSPARENT_HUGEPAGE
>   config PGTABLE_HAS_HUGE_LEAVES
>   	def_bool TRANSPARENT_HUGEPAGE || HUGETLB_PAGE
>   
> +# TODO: Allow to be enabled without THP
> +config ARCH_SUPPORTS_HUGE_PFNMAP
> +	def_bool n
> +	depends on TRANSPARENT_HUGEPAGE
> +
> +config ARCH_SUPPORTS_PMD_PFNMAP
> +	def_bool y
> +	depends on ARCH_SUPPORTS_HUGE_PFNMAP && HAVE_ARCH_TRANSPARENT_HUGEPAGE
> +
> +config ARCH_SUPPORTS_PUD_PFNMAP
> +	def_bool y
> +	depends on ARCH_SUPPORTS_HUGE_PFNMAP && HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
> +
>   #
>   # UP and nommu archs use km based percpu allocator
>   #

As noted in reply to other patches, I think you have to take care of 
vm_normal_page_pmd() [if not done in another patch I am missing] and 
likely you want to introduce vm_normal_page_pud().

-- 
Cheers,

David / dhildenb