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

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Message-ID: <ZrZPA_Enghb42xMq@x1n>
Date: Fri, 9 Aug 2024 13:16:51 -0400
From: Peter Xu <peterx@...hat.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	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 Fri, Aug 09, 2024 at 06:34:15PM +0200, David Hildenbrand wrote:
> 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().

So far this patch may not have direct involvement with vm_normal_page_pud()
yet?  Anyway, let's keep the discussion there, then we'll know how to move
on.

Thanks,

-- 
Peter Xu