+long get_user_pages_longterm(unsigned long start, unsigned long nr_pages,

• unsigned int gup_flags, struct page **pages,
  

• struct vm_area_struct **vmas)
  

+{

• struct vm_area_struct **__vmas = vmas;

How about calling the vma argument vma_arg, and the one used vma to make thigns a little more readable?

• struct vm_area_struct *vma_prev = NULL;
• long rc, i;
• if (!pages)

• return -EINVAL;
  

• if (!vmas && IS_ENABLED(CONFIG_FS_DAX)) {

• __vmas = kzalloc(sizeof(struct vm_area_struct *) * nr_pages,
  

• 		GFP_KERNEL);
  

• if (!__vmas)
  

• 	return -ENOMEM;
  

• }
• rc = get_user_pages(start, nr_pages, gup_flags, pages, __vmas);
• /* skip scan for fs-dax vmas if they are compile time disabled */
• if (!IS_ENABLED(CONFIG_FS_DAX))

• goto out;
  

Instead of all this IS_ENABLED magic I'd recomment to just conditionally compile this function and define it to get_user_pages in the header if FS_DAX is disabled.

Else this looks fine to me.