Re: [PATCH 01/19] mm: Introduce ARCH_SUPPORTS_HUGE_PFNMAP and special bits to pmd/pud

David Hildenbrand
2024-08-09T18:06:49Z

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@redhat.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