[PATCH v4 15/25] huge_memory: Add vmf_insert_folio_pud()
David Hildenbrand
david at redhat.com
Fri Dec 20 10:52:43 PST 2024
On 17.12.24 06:12, Alistair Popple wrote:
> Currently DAX folio/page reference counts are managed differently to
> normal pages. To allow these to be managed the same as normal pages
> introduce vmf_insert_folio_pud. This will map the entire PUD-sized folio
> and take references as it would for a normally mapped page.
>
> This is distinct from the current mechanism, vmf_insert_pfn_pud, which
> simply inserts a special devmap PUD entry into the page table without
> holding a reference to the page for the mapping.
>
> Signed-off-by: Alistair Popple <apopple at nvidia.com>
> ---
> include/linux/huge_mm.h | 11 +++++-
> mm/huge_memory.c | 96 ++++++++++++++++++++++++++++++++++++------
> 2 files changed, 95 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 93e509b..012137b 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -39,6 +39,7 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>
> vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write);
> vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write);
> +vm_fault_t vmf_insert_folio_pud(struct vm_fault *vmf, struct folio *folio, bool write);
>
> enum transparent_hugepage_flag {
> TRANSPARENT_HUGEPAGE_UNSUPPORTED,
> @@ -458,6 +459,11 @@ static inline bool is_huge_zero_pmd(pmd_t pmd)
> return pmd_present(pmd) && READ_ONCE(huge_zero_pfn) == pmd_pfn(pmd);
> }
>
> +static inline bool is_huge_zero_pud(pud_t pud)
> +{
> + return false;
> +}
> +
> struct folio *mm_get_huge_zero_folio(struct mm_struct *mm);
> void mm_put_huge_zero_folio(struct mm_struct *mm);
>
> @@ -604,6 +610,11 @@ static inline bool is_huge_zero_pmd(pmd_t pmd)
> return false;
> }
>
> +static inline bool is_huge_zero_pud(pud_t pud)
> +{
> + return false;
> +}
> +
I'm really not a fan of these, because I assume we will never ever
implement these any time soon. (who will waste 1 GiG or more on faster
reading of 0s?)
> static inline void mm_put_huge_zero_folio(struct mm_struct *mm)
> {
> return;
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 120cd2c..5081808 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1482,19 +1482,17 @@ static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
> struct mm_struct *mm = vma->vm_mm;
> pgprot_t prot = vma->vm_page_prot;
> pud_t entry;
> - spinlock_t *ptl;
>
> - ptl = pud_lock(mm, pud);
> if (!pud_none(*pud)) {
> if (write) {
> if (WARN_ON_ONCE(pud_pfn(*pud) != pfn_t_to_pfn(pfn)))
> - goto out_unlock;
> + return;
> entry = pud_mkyoung(*pud);
> entry = maybe_pud_mkwrite(pud_mkdirty(entry), vma);
> if (pudp_set_access_flags(vma, addr, pud, entry, 1))
> update_mmu_cache_pud(vma, addr, pud);
> }
> - goto out_unlock;
> + return;
> }
>
> entry = pud_mkhuge(pfn_t_pud(pfn, prot));
> @@ -1508,9 +1506,6 @@ static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
> }
> set_pud_at(mm, addr, pud, entry);
> update_mmu_cache_pud(vma, addr, pud);
> -
> -out_unlock:
> - spin_unlock(ptl);
> }
>
> /**
> @@ -1528,6 +1523,7 @@ vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write)
> unsigned long addr = vmf->address & PUD_MASK;
> struct vm_area_struct *vma = vmf->vma;
> pgprot_t pgprot = vma->vm_page_prot;
> + spinlock_t *ptl;
>
> /*
> * If we had pud_special, we could avoid all these restrictions,
> @@ -1545,10 +1541,55 @@ vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write)
>
> track_pfn_insert(vma, &pgprot, pfn);
>
> + ptl = pud_lock(vma->vm_mm, vmf->pud);
> insert_pfn_pud(vma, addr, vmf->pud, pfn, write);
> + spin_unlock(ptl);
> +
> return VM_FAULT_NOPAGE;
> }
> EXPORT_SYMBOL_GPL(vmf_insert_pfn_pud);
> +
> +/**
> + * vmf_insert_folio_pud - insert a pud size folio mapped by a pud entry
> + * @vmf: Structure describing the fault
> + * @pfn: pfn of the page to insert
> + * @write: whether it's a write fault
> + *
> + * Return: vm_fault_t value.
> + */
> +vm_fault_t vmf_insert_folio_pud(struct vm_fault *vmf, struct folio *folio, bool write)
> +{
> + struct vm_area_struct *vma = vmf->vma;
> + unsigned long addr = vmf->address & PUD_MASK;
> + pfn_t pfn = pfn_to_pfn_t(folio_pfn(folio));
> + pud_t *pud = vmf->pud;
> + pgprot_t prot = vma->vm_page_prot;
See below, pfn, prot and page can likely go.
> + struct mm_struct *mm = vma->vm_mm;
> + spinlock_t *ptl;
> + struct page *page;
> +
> + if (addr < vma->vm_start || addr >= vma->vm_end)
> + return VM_FAULT_SIGBUS;
> +
> + if (WARN_ON_ONCE(folio_order(folio) != PUD_ORDER))
> + return VM_FAULT_SIGBUS;
> +
> + track_pfn_insert(vma, &prot, pfn);
Oh, why is that required? We are inserting a folio and start messing
with VM_PAT on x86 that only applies to VM_PFNMAP mappings? :)
> +
> + ptl = pud_lock(mm, pud);
> + if (pud_none(*vmf->pud)) {
> + page = pfn_t_to_page(pfn);
Why are we suddenly working with that pfn_t whichcraft? :)
> + folio = page_folio(page);
Ehm, you got the folio ... passed into this function?
Why can't that simply be
folio_get(folio);
folio_add_file_rmap_pud(folio, folio_page(folio, 0), vma);
> + folio_get(folio);
> + folio_add_file_rmap_pud(folio, page, vma);
> + add_mm_counter(mm, mm_counter_file(folio), HPAGE_PUD_NR);
> + }
> + insert_pfn_pud(vma, addr, vmf->pud, pfn, write);
> + spin_unlock(ptl);
> +
> + return VM_FAULT_NOPAGE;
> +}
> +EXPORT_SYMBOL_GPL(vmf_insert_folio_pud);
> #endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
>
> void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
> @@ -2146,7 +2187,8 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
> zap_deposited_table(tlb->mm, pmd);
> spin_unlock(ptl);
> } else if (is_huge_zero_pmd(orig_pmd)) {
> - zap_deposited_table(tlb->mm, pmd);
> + if (!vma_is_dax(vma) || arch_needs_pgtable_deposit())
> + zap_deposited_table(tlb->mm, pmd);
> spin_unlock(ptl);
> } else {
> struct folio *folio = NULL;
> @@ -2634,12 +2676,24 @@ int zap_huge_pud(struct mmu_gather *tlb, struct vm_area_struct *vma,
> orig_pud = pudp_huge_get_and_clear_full(vma, addr, pud, tlb->fullmm);
> arch_check_zapped_pud(vma, orig_pud);
> tlb_remove_pud_tlb_entry(tlb, pud, addr);
> - if (vma_is_special_huge(vma)) {
> + if (!vma_is_dax(vma) && vma_is_special_huge(vma)) {
> spin_unlock(ptl);
> /* No zero page support yet */
> } else {
> - /* No support for anonymous PUD pages yet */
> - BUG();
> + struct page *page = NULL;
> + struct folio *folio;
> +
> + /* No support for anonymous PUD pages or migration yet */
> + BUG_ON(vma_is_anonymous(vma) || !pud_present(orig_pud));
VM_WARN_ON_ONCE().
> +
> + page = pud_page(orig_pud);
> + folio = page_folio(page);
> + folio_remove_rmap_pud(folio, page, vma);
> + VM_BUG_ON_PAGE(!PageHead(page), page);
Please drop that or so something like
VM_WARN_ON_ONCE(page != folio_page(folio, 0));
> + add_mm_counter(tlb->mm, mm_counter_file(folio), -HPAGE_PUD_NR);
> +
> + spin_unlock(ptl);
> + tlb_remove_page_size(tlb, page, HPAGE_PUD_SIZE);
> }
> return 1;
> }
> @@ -2647,6 +2701,8 @@ int zap_huge_pud(struct mmu_gather *tlb, struct vm_area_struct *vma,
> static void __split_huge_pud_locked(struct vm_area_struct *vma, pud_t *pud,
> unsigned long haddr)
> {
> + pud_t old_pud;
> +
> VM_BUG_ON(haddr & ~HPAGE_PUD_MASK);
> VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
> VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PUD_SIZE, vma);
> @@ -2654,7 +2710,23 @@ static void __split_huge_pud_locked(struct vm_area_struct *vma, pud_t *pud,
>
> count_vm_event(THP_SPLIT_PUD);
>
> - pudp_huge_clear_flush(vma, haddr, pud);
> + old_pud = pudp_huge_clear_flush(vma, haddr, pud);
> + if (is_huge_zero_pud(old_pud))
> + return;
> +
> + if (vma_is_dax(vma)) {
Maybe you want
if (!vma_is_dax(vma))
return;
To then reduce alignment. I suspect all other splitting code (besides
anon memory) will want to do the same thing here in the future.
--
Cheers,
David / dhildenb
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