@@ -3936,8 +3936,6 @@ __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));
@@ -4033,6 +4031,18 @@ 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);