On 10.01.25 07:00, 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@xxxxxxxxxx>
[...]
+/**
+ * vmf_insert_folio_pud - insert a pud size folio mapped by a pud entry
+ * @vmf: Structure describing the fault
+ * @folio: folio 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;
+ pud_t *pud = vmf->pud;
+ struct mm_struct *mm = vma->vm_mm;
+ spinlock_t *ptl;
+
+ 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;
+
+ ptl = pud_lock(mm, pud);
+ if (pud_none(*vmf->pud)) {
+ folio_get(folio);
+ folio_add_file_rmap_pud(folio, &folio->page, vma);
+ add_mm_counter(mm, mm_counter_file(folio), HPAGE_PUD_NR);
+ }
+ insert_pfn_pud(vma, addr, vmf->pud, pfn_to_pfn_t(folio_pfn(folio)), write);
This looks scary at first (inserting something when not taking a
reference), but insert_pfn_pud() seems to handle that. A comment here
would have been nice.
It's weird, though, that if there is already something else, that we
only WARN but don't actually return an error. So ...
+ spin_unlock(ptl);
+
+ return VM_FAULT_NOPAGE;
I assume always returning VM_FAULT_NOPAGE, even when something went
wrong, is the right thing to do?
Apart from that LGTM.
--
Cheers,
David / dhildenb
