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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index ea0e23fd6967..e1b6f4e13b91 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -733,6 +733,16 @@ 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))
+                                return VM_FAULT_OOM;
+                        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)) {