mm: page_remove_rmap comments on PageAnon

[safe/jmp/linux-2.6] / mm / rmap.c

diff --git a/mm/rmap.c b/mm/rmap.c
index 94a5246..0597747 100644 (file)
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -422,7 +422,7 @@ int page_referenced(struct page *page, int is_locked,
                        referenced += page_referenced_anon(page, mem_cont);
                else if (is_locked)
                        referenced += page_referenced_file(page, mem_cont);
-               else if (TestSetPageLocked(page))
+               else if (!trylock_page(page))
                        referenced++;
                else {
                        if (page->mapping)
@@ -659,23 +659,30 @@ 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.
+                */
        }
 }