mm: memory: use a folio in do_cow_fault()

Use folio_prealloc() helper and convert to use a folio in do_cow_fault(),
which save five compound_head() calls.

Link: https://lkml.kernel.org/r/20231118023232.1409103-5-wangkefeng.wang@huawei.comSigned-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memory.c

@@ -4656,6 +4656,7 @@ static vm_fault_t do_read_fault(struct vm_fault *vmf)
 static vm_fault_t do_cow_fault(struct vm_fault *vmf)
 {
 	struct vm_area_struct *vma = vmf->vma;
+	struct folio *folio;
 	vm_fault_t ret;
 
 	ret = vmf_can_call_fault(vmf);
@@ -4664,16 +4665,11 @@ static vm_fault_t do_cow_fault(struct vm_fault *vmf)
 	if (ret)
 		return ret;
 
-	vmf->cow_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vmf->address);
-	if (!vmf->cow_page)
+	folio = folio_prealloc(vma->vm_mm, vma, vmf->address, false);
+	if (!folio)
 		return VM_FAULT_OOM;
 
-	if (mem_cgroup_charge(page_folio(vmf->cow_page), vma->vm_mm,
-				GFP_KERNEL)) {
-		put_page(vmf->cow_page);
-		return VM_FAULT_OOM;
-	}
-	folio_throttle_swaprate(page_folio(vmf->cow_page), GFP_KERNEL);
+	vmf->cow_page = &folio->page;
 
 	ret = __do_fault(vmf);
 	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
@@ -4682,7 +4678,7 @@ static vm_fault_t do_cow_fault(struct vm_fault *vmf)
 		return ret;
 
 	copy_user_highpage(vmf->cow_page, vmf->page, vmf->address, vma);
-	__SetPageUptodate(vmf->cow_page);
+	__folio_mark_uptodate(folio);
 
 	ret |= finish_fault(vmf);
 	unlock_page(vmf->page);
@@ -4691,7 +4687,7 @@ static vm_fault_t do_cow_fault(struct vm_fault *vmf)
 		goto uncharge_out;
 	return ret;
 uncharge_out:
-	put_page(vmf->cow_page);
+	folio_put(folio);
 	return ret;
 }