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

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Message-ID: <04d06717-4d44-4e09-a3cb-d8350e3466ad@redhat.com>
Date: Fri, 9 Aug 2024 20:06:42 +0200
From: David Hildenbrand <david@...hat.com>
To: Peter Xu <peterx@...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 09.08.24 19:16, Peter Xu wrote:
> 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.

vm_normal_page_pud() might make sense as of today already, primarily to 
wrap the pud_devmap() stuff (maybe that is gone soon, who knows). 
Anyhow, I can send a patch to add that as well.

-- 
Cheers,

David / dhildenb