On 8 May 2024, at 1:43, Lance Yang wrote:
> On Tue, May 7, 2024 at 11:26 PM Zi Yan <ziy@xxxxxxxxxx> wrote:
>>
>> On 1 May 2024, at 0:26, Lance Yang wrote:
>>
>>> In preparation for supporting try_to_unmap_one() to unmap PMD-mapped
>>> folios, start the pagewalk first, then call split_huge_pmd_address()
>>> to split the folio.
>>>
>>> Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
>>> Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx>
>>> ---
>>> include/linux/huge_mm.h | 20 ++++++++++++++++++++
>>> mm/huge_memory.c | 42 +++++++++++++++++++++--------------------
>>> mm/rmap.c | 24 +++++++++++++++++------
>>> 3 files changed, 60 insertions(+), 26 deletions(-)
>>>
>>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>>> index c8d3ec116e29..38c4b5537715 100644
>>> --- a/include/linux/huge_mm.h
>>> +++ b/include/linux/huge_mm.h
>>> @@ -409,6 +409,20 @@ static inline bool thp_migration_supported(void)
>>> return IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION);
>>> }
>>>
>>> +void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address,
>>> + pmd_t *pmd, bool freeze, struct folio *folio);
>>> +
>>> +static inline void align_huge_pmd_range(struct vm_area_struct *vma,
>>> + unsigned long *start,
>>> + unsigned long *end)
>>> +{
>>> + *start = ALIGN(*start, HPAGE_PMD_SIZE);
>>> + *end = ALIGN_DOWN(*end, HPAGE_PMD_SIZE);
>>> +
>>> + VM_WARN_ON_ONCE(vma->vm_start > *start);
>>> + VM_WARN_ON_ONCE(vma->vm_end < *end);
>>> +}
>>> +
>>> #else /* CONFIG_TRANSPARENT_HUGEPAGE */
>>>
>>> static inline bool folio_test_pmd_mappable(struct folio *folio)
>>> @@ -471,6 +485,12 @@ static inline void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
>>> unsigned long address, bool freeze, struct folio *folio) {}
>>> static inline void split_huge_pmd_address(struct vm_area_struct *vma,
>>> unsigned long address, bool freeze, struct folio *folio) {}
>>> +static inline void split_huge_pmd_locked(struct vm_area_struct *vma,
>>> + unsigned long address, pmd_t *pmd,
>>> + bool freeze, struct folio *folio) {}
>>> +static inline void align_huge_pmd_range(struct vm_area_struct *vma,
>>> + unsigned long *start,
>>> + unsigned long *end) {}
>>>
>>> #define split_huge_pud(__vma, __pmd, __address) \
>>> do { } while (0)
>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>>> index 8261b5669397..145505a1dd05 100644
>>> --- a/mm/huge_memory.c
>>> +++ b/mm/huge_memory.c
>>> @@ -2584,6 +2584,27 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
>>> pmd_populate(mm, pmd, pgtable);
>>> }
>>>
>>> +void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address,
>>> + pmd_t *pmd, bool freeze, struct folio *folio)
>>> +{
>>> + VM_WARN_ON_ONCE(folio && !folio_test_pmd_mappable(folio));
>>> + VM_WARN_ON_ONCE(!IS_ALIGNED(address, HPAGE_PMD_SIZE));
>>> + VM_WARN_ON_ONCE(folio && !folio_test_locked(folio));
>>> + VM_BUG_ON(freeze && !folio);
>>> +
>>> + /*
>>> + * When the caller requests to set up a migration entry, we
>>> + * require a folio to check the PMD against. Otherwise, there
>>> + * is a risk of replacing the wrong folio.
>>> + */
>>> + if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) ||
>>> + is_pmd_migration_entry(*pmd)) {
>>> + if (folio && folio != pmd_folio(*pmd))
>>> + return;
>>> + __split_huge_pmd_locked(vma, pmd, address, freeze);
>>> + }
>>> +}
>>> +
>>> void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
>>> unsigned long address, bool freeze, struct folio *folio)
>>> {
>>> @@ -2595,26 +2616,7 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
>>> (address & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE);
>>> mmu_notifier_invalidate_range_start(&range);
>>> ptl = pmd_lock(vma->vm_mm, pmd);
>>> -
>>> - /*
>>> - * If caller asks to setup a migration entry, we need a folio to check
>>> - * pmd against. Otherwise we can end up replacing wrong folio.
>>> - */
>>> - VM_BUG_ON(freeze && !folio);
>>> - VM_WARN_ON_ONCE(folio && !folio_test_locked(folio));
>>> -
>>> - if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) ||
>>> - is_pmd_migration_entry(*pmd)) {
>>> - /*
>>> - * It's safe to call pmd_page when folio is set because it's
>>> - * guaranteed that pmd is present.
>>> - */
>>> - if (folio && folio != pmd_folio(*pmd))
>>> - goto out;
>>> - __split_huge_pmd_locked(vma, pmd, range.start, freeze);
>>> - }
>>> -
>>> -out:
>>> + split_huge_pmd_locked(vma, range.start, pmd, freeze, folio);
>>> spin_unlock(ptl);
>>> mmu_notifier_invalidate_range_end(&range);
>>> }
>>> diff --git a/mm/rmap.c b/mm/rmap.c
>>> index 7e2575d669a9..432601154583 100644
>>> --- a/mm/rmap.c
>>> +++ b/mm/rmap.c
>>> @@ -1636,9 +1636,6 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
>>> if (flags & TTU_SYNC)
>>> pvmw.flags = PVMW_SYNC;
>>>
>>> - if (flags & TTU_SPLIT_HUGE_PMD)
>>> - split_huge_pmd_address(vma, address, false, folio);
>>> -
>>> /*
>>> * For THP, we have to assume the worse case ie pmd for invalidation.
>>> * For hugetlb, it could be much worse if we need to do pud
>>> @@ -1650,6 +1647,8 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
>>> range.end = vma_address_end(&pvmw);
>>> mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm,
>>> address, range.end);
>>> + if (flags & TTU_SPLIT_HUGE_PMD)
>>> + align_huge_pmd_range(vma, &range.start, &range.end);
>>> if (folio_test_hugetlb(folio)) {
>>> /*
>>> * If sharing is possible, start and end will be adjusted
>>> @@ -1664,9 +1663,6 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
>>> mmu_notifier_invalidate_range_start(&range);
>>>
>>> while (page_vma_mapped_walk(&pvmw)) {
>>> - /* Unexpected PMD-mapped THP? */
>>> - VM_BUG_ON_FOLIO(!pvmw.pte, folio);
>>> -
>>> /*
>>> * If the folio is in an mlock()d vma, we must not swap it out.
>>> */
>>> @@ -1678,6 +1674,22 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
>>> goto walk_done_err;
>>> }
>>>
>>> + if (!pvmw.pte && (flags & TTU_SPLIT_HUGE_PMD)) {
>>> + /*
>>> + * We temporarily have to drop the PTL and start once
>>> + * again from that now-PTE-mapped page table.
>>> + */
>>> + split_huge_pmd_locked(vma, range.start, pvmw.pmd, false,
>>> + folio);
>>
>> Just in case you might miss here, since you will no longer align
>> range.start as Baolin mentioned in another email and you have a VM_WARN_ONCE
>> in split_huge_pmd_locked(), you will need to align the input address now.
>
> Thanks for bringing that up!
>
> I do miss the alignment here when I decide to no longer align range.start
> in another email - thanks!
>
No problem.
> Zi, could I move the alignment here?
> IIUC, we will not encounter a partially mapped THP here, and range.start
> and range.end should also not beyond the VMA limits.
>
> align_huge_pmd_range(vma, &range.start, &range.end);
> split_huge_pmd_locked(vma, range.start, pvmw.pmd, false,
> folio);
I think you can just do
split_huge_pmd_locked(vma, ALIGN(range.start, HPAGE_PMD_SIZE), pvmw.pmd, false, folio);
since range will later be used by mmu_notifier_invalidate_range_end() and changing
it might cause secondary TLB invalidation issues.
>
> Thanks,
> Lance
>
>>
>>> + pvmw.pmd = NULL;
>>> + spin_unlock(pvmw.ptl);
>>> + flags &= ~TTU_SPLIT_HUGE_PMD;
>>> + continue;
>>> + }
>>> +
>>> + /* Unexpected PMD-mapped THP? */
>>> + VM_BUG_ON_FOLIO(!pvmw.pte, folio);
>>> +
>>> pfn = pte_pfn(ptep_get(pvmw.pte));
>>> subpage = folio_page(folio, pfn - folio_pfn(folio));
>>> address = pvmw.address;
>>> --
>>> 2.33.1
>>
>>
>> --
>> Best Regards,
>> Yan, Zi
--
Best Regards,
Yan, Zi
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