3 files changed, 11 insertions, 7 deletions

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 69407f85e10b..fed6f5e0b411 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -102,7 +102,7 @@ int try_to_unmap(struct page *, int ignore_refs);
  * Called from mm/filemap_xip.c to unmap empty zero page
  */
 pte_t *page_check_address(struct page *, struct mm_struct *,
-                                unsigned long, spinlock_t **);
+                                unsigned long, spinlock_t **, int);
 
 /*
  * Used by swapoff to help locate where page is expected in vma.
diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c
index 380ab402d711..8b710ca13247 100644
--- a/mm/filemap_xip.c
+++ b/mm/filemap_xip.c
@@ -185,7 +185,7 @@ __xip_unmap (struct address_space * mapping,
                 address = vma->vm_start +
                         ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
                 BUG_ON(address < vma->vm_start || address >= vma->vm_end);
-                pte = page_check_address(page, mm, address, &ptl);
+                pte = page_check_address(page, mm, address, &ptl, 1);
                 if (pte) {
                         /* Nuke the page table entry. */
                         flush_cache_page(vma, address, pte_pfn(*pte));
diff --git a/mm/rmap.c b/mm/rmap.c
index 059774712c08..0383acfcb068 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -224,10 +224,14 @@ unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
 /*
  * Check that @page is mapped at @address into @mm.
  *
+ * If @sync is false, page_check_address may perform a racy check to avoid
+ * the page table lock when the pte is not present (helpful when reclaiming
+ * highly shared pages).
+ *
  * On success returns with pte mapped and locked.
  */
 pte_t *page_check_address(struct page *page, struct mm_struct *mm,
-                          unsigned long address, spinlock_t **ptlp)
+                          unsigned long address, spinlock_t **ptlp, int sync)
 {
         pgd_t *pgd;
         pud_t *pud;
@@ -249,7 +253,7 @@ pte_t *page_check_address(struct page *page, struct mm_struct *mm,
 
         pte = pte_offset_map(pmd, address);
         /* Make a quick check before getting the lock */
-        if (!pte_present(*pte)) {
+        if (!sync && !pte_present(*pte)) {
                 pte_unmap(pte);
                 return NULL;
         }
@@ -281,7 +285,7 @@ static int page_referenced_one(struct page *page,
         if (address == -EFAULT)
                 goto out;
 
-        pte = page_check_address(page, mm, address, &ptl);
+        pte = page_check_address(page, mm, address, &ptl, 0);
         if (!pte)
                 goto out;
 
@@ -450,7 +454,7 @@ static int page_mkclean_one(struct page *page, struct vm_area_struct *vma)
         if (address == -EFAULT)
                 goto out;
 
-        pte = page_check_address(page, mm, address, &ptl);
+        pte = page_check_address(page, mm, address, &ptl, 1);
         if (!pte)
                 goto out;
 
@@ -704,7 +708,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
         if (address == -EFAULT)
                 goto out;
 
-        pte = page_check_address(page, mm, address, &ptl);
+        pte = page_check_address(page, mm, address, &ptl, 0);
         if (!pte)
                 goto out;