Re: [PATCH v3 4/6] mm/thp: add THP allocation helper

+#ifdef CONFIG_TRANSPARENT_HUGEPAGE +extern struct page *alloc_transhugepage(struct vm_area_struct *vma,

• 			unsigned long addr);
  

No need for the extern. And also here: do we actually need the stub, or can the caller make sure (using IS_ENABLED and similar) that the compiler knows the code is dead?

+struct page *alloc_transhugepage(struct vm_area_struct *vma,

• 		 unsigned long haddr)
  

+{

• gfp_t gfp;
• struct page *page;
• gfp = alloc_hugepage_direct_gfpmask(vma);
• page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
• if (page)

• prep_transhuge_page(page);
  

• return page;

I think do_huge_pmd_anonymous_page should be switched to use this helper as well.