[RFC PATCH 1/5] mm: memory: extend finish_fault() to support large folio

[Baolin Wang]

Add large folio mapping establishment support for finish_fault() as a preparation,
to support multi-size THP allocation of anonymous shared pages in the following
patches.

Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
 mm/memory.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index b6fa5146b260..094a76730776 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4766,7 +4766,10 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
 {
 	struct vm_area_struct *vma = vmf->vma;
 	struct page *page;
+	struct folio *folio;
 	vm_fault_t ret;
+	int nr_pages, i;
+	unsigned long addr;
 
 	/* Did we COW the page? */
 	if ((vmf->flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED))
@@ -4797,22 +4800,30 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
 			return VM_FAULT_OOM;
 	}
 
+	folio = page_folio(page);
+	nr_pages = folio_nr_pages(folio);
+	addr = ALIGN_DOWN(vmf->address, nr_pages * PAGE_SIZE);
 	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
-				      vmf->address, &vmf->ptl);
+				       addr, &vmf->ptl);
 	if (!vmf->pte)
 		return VM_FAULT_NOPAGE;
 
 	/* Re-check under ptl */
-	if (likely(!vmf_pte_changed(vmf))) {
-		struct folio *folio = page_folio(page);
-
-		set_pte_range(vmf, folio, page, 1, vmf->address);
-		ret = 0;
-	} else {
+	if (nr_pages == 1 && vmf_pte_changed(vmf)) {
 		update_mmu_tlb(vma, vmf->address, vmf->pte);
 		ret = VM_FAULT_NOPAGE;
+		goto unlock;
+	} else if (nr_pages > 1 && !pte_range_none(vmf->pte, nr_pages)) {
+		for (i = 0; i < nr_pages; i++)
+			update_mmu_tlb(vma, addr + PAGE_SIZE * i, vmf->pte + i);
+		ret = VM_FAULT_NOPAGE;
+		goto unlock;
 	}
 
+	set_pte_range(vmf, folio, &folio->page, nr_pages, addr);
+	ret = 0;
+
+unlock:
 	pte_unmap_unlock(vmf->pte, vmf->ptl);
 	return ret;
 }
-- 
2.39.3