thp: setup huge zero page on non-write page fault

All code paths seems covered. Now we can map huge zero page on read page
fault.

We setup it in do_huge_pmd_anonymous_page() if area around fault address
is suitable for THP and we've got read page fault.

If we fail to setup huge zero page (ENOMEM) we fallback to
handle_pte_fault() as we normally do in THP.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@linux.intel.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 62209b018aaead57b9adb6b18731fbd0decd6813..58e8004243a67bb27588d9749808ef5211020996 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -734,6 +734,16 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
                        return VM_FAULT_OOM;
                if (unlikely(khugepaged_enter(vma)))
                        return VM_FAULT_OOM;
+               if (!(flags & FAULT_FLAG_WRITE)) {
+                       pgtable_t pgtable;
+                       pgtable = pte_alloc_one(mm, haddr);
+                       if (unlikely(!pgtable))
+                               goto out;
+                       spin_lock(&mm->page_table_lock);
+                       set_huge_zero_page(pgtable, mm, vma, haddr, pmd);
+                       spin_unlock(&mm->page_table_lock);
+                       return 0;
+               }
                page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),
                                          vma, haddr, numa_node_id(), 0);
                if (unlikely(!page)) {