Merge 3.10-rc3 into char-misc-next

We want the changes in here.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 12 insertions, 2 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index cb1c9dedf9b6..010d6c14129a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4108,8 +4108,6 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype,
 	if (mem_cgroup_disabled())
 		return NULL;
 
-	VM_BUG_ON(PageSwapCache(page));
-
 	if (PageTransHuge(page)) {
 		nr_pages <<= compound_order(page);
 		VM_BUG_ON(!PageTransHuge(page));
@@ -4205,6 +4203,18 @@ void mem_cgroup_uncharge_page(struct page *page)
 	if (page_mapped(page))
 		return;
 	VM_BUG_ON(page->mapping && !PageAnon(page));
+	/*
+	 * If the page is in swap cache, uncharge should be deferred
+	 * to the swap path, which also properly accounts swap usage
+	 * and handles memcg lifetime.
+	 *
+	 * Note that this check is not stable and reclaim may add the
+	 * page to swap cache at any time after this.  However, if the
+	 * page is not in swap cache by the time page->mapcount hits
+	 * 0, there won't be any page table references to the swap
+	 * slot, and reclaim will free it and not actually write the
+	 * page to disk.
+	 */
 	if (PageSwapCache(page))
 		return;
 	__mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_ANON, false);