mm: fix for infinite churning of mlocked pages

An mlocked page might lose the isolatation race.  This causes the page to
clear PG_mlocked while it remains in a VM_LOCKED vma.  This means it can
be put onto the [in]active list.  We can rescue it by using try_to_unmap()
in shrink_page_list().

But now, As Wu Fengguang pointed out, vmscan has a bug.  If the page has
PG_referenced, it can't reach try_to_unmap() in shrink_page_list() but is
put into the active list.  If the page is referenced repeatedly, it can
remain on the [in]active list without being moving to the unevictable
list.

This patch fixes it.

Reported-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: KOSAKI Motohiro <<kosaki.motohiro@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index dea7abd31098..94e86dd6954c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -630,9 +630,14 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 
                 referenced = page_referenced(page, 1,
                                                 sc->mem_cgroup, &vm_flags);
-                /* In active use or really unfreeable?  Activate it. */
+                /*
+                 * In active use or really unfreeable?  Activate it.
+                 * If page which have PG_mlocked lost isoltation race,
+                 * try_to_unmap moves it to unevictable list
+                 */
                 if (sc->order <= PAGE_ALLOC_COSTLY_ORDER &&
-                                        referenced && page_mapping_inuse(page))
+                                        referenced && page_mapping_inuse(page)
+                                        && !(vm_flags & VM_LOCKED))
                         goto activate_locked;
 
                 /*