From: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Date: Thu, 29 Nov 2012 03:17:38 +0000 (+1100)
Subject: thp: setup huge zero page on non-write page fault
X-Git-Tag: next-20121205~1^2~262
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=7020973db6edb5e03b246c332191be1f981a4a7b;p=karo-tx-linux.git

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 62209b018aae..58e8004243a6 100644
--- 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)) {