1 files changed, 25 insertions, 14 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 1ea4e6fcee77..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;
 
@@ -659,23 +663,30 @@ void page_remove_rmap(struct page *page, struct vm_area_struct *vma)
                 }
 
                 /*
-                 * It would be tidy to reset the PageAnon mapping here,
-                 * but that might overwrite a racing page_add_anon_rmap
-                 * which increments mapcount after us but sets mapping
-                 * before us: so leave the reset to free_hot_cold_page,
-                 * and remember that it's only reliable while mapped.
-                 * Leaving it set also helps swapoff to reinstate ptes
-                 * faster for those pages still in swapcache.
+                 * Now that the last pte has gone, s390 must transfer dirty
+                 * flag from storage key to struct page.  We can usually skip
+                 * this if the page is anon, so about to be freed; but perhaps
+                 * not if it's in swapcache - there might be another pte slot
+                 * containing the swap entry, but page not yet written to swap.
                  */
                 if ((!PageAnon(page) || PageSwapCache(page)) &&
                     page_test_dirty(page)) {
                         page_clear_dirty(page);
                         set_page_dirty(page);
                 }
-                mem_cgroup_uncharge_page(page);
 
+                mem_cgroup_uncharge_page(page);
                 __dec_zone_page_state(page,
-                                PageAnon(page) ? NR_ANON_PAGES : NR_FILE_MAPPED);
+                        PageAnon(page) ? NR_ANON_PAGES : NR_FILE_MAPPED);
+                /*
+                 * It would be tidy to reset the PageAnon mapping here,
+                 * but that might overwrite a racing page_add_anon_rmap
+                 * which increments mapcount after us but sets mapping
+                 * before us: so leave the reset to free_hot_cold_page,
+                 * and remember that it's only reliable while mapped.
+                 * Leaving it set also helps swapoff to reinstate ptes
+                 * faster for those pages still in swapcache.
+                 */
         }
 }
 
@@ -697,7 +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;