hugetlb, rmap: always use anon_vma root pointer

This patch applies Andrea's fix given by the following patch into hugepage
rmapping code:

  commit 288468c334e98aacbb7e2fb8bde6bc1adcd55e05
  Author: Andrea Arcangeli <aarcange@redhat.com>
  Date:   Mon Aug 9 17:19:09 2010 -0700

This patch uses anon_vma->root and avoids unnecessary overwriting when
anon_vma is already set up.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Acked-by: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 6 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index f6f0d2dda2ea..2854857fd63b 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1564,13 +1564,14 @@ static void __hugepage_set_anon_rmap(struct page *page,
         struct vm_area_struct *vma, unsigned long address, int exclusive)
 {
         struct anon_vma *anon_vma = vma->anon_vma;
+
         BUG_ON(!anon_vma);
-        if (!exclusive) {
-                struct anon_vma_chain *avc;
-                avc = list_entry(vma->anon_vma_chain.prev,
-                                 struct anon_vma_chain, same_vma);
-                anon_vma = avc->anon_vma;
-        }
+
+        if (PageAnon(page))
+                return;
+        if (!exclusive)
+                anon_vma = anon_vma->root;
+
         anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
         page->mapping = (struct address_space *) anon_vma;
         page->index = linear_page_index(vma, address);