diff --git a/arch/s390/include/asm/page.h b/arch/s390/include/asm/page.h
index 6d5367060a5656a92d5d1b95f28dc3097fa47e78..39faa4ac966075298ea1d6fb1843d9c85cf792a5 100644
--- a/arch/s390/include/asm/page.h
+++ b/arch/s390/include/asm/page.h
@@ -158,6 +158,9 @@ static inline int page_reset_referenced(unsigned long addr)
  * race against modification of the referenced bit. This function
  * should therefore only be called if it is not mapped in any
  * address space.
+ *
+ * Note that the bit gets set whenever page content is changed. That means
+ * also when the page is modified by DMA or from inside the kernel.
  */
 #define __HAVE_ARCH_PAGE_TEST_AND_CLEAR_DIRTY
 static inline int page_test_and_clear_dirty(unsigned long pfn, int mapped)
diff --git a/mm/rmap.c b/mm/rmap.c
index 46823fb0e801b599178f8bd548437fa03d87b8ef..cf7e99a87c32865c4e6cf5b6ed4f48f7f05aa9e0 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1151,9 +1151,11 @@ void page_remove_rmap(struct page *page)
 	 * containing the swap entry, but page not yet written to swap.
 	 *
 	 * And we can skip it on file pages, so long as the filesystem
-	 * participates in dirty tracking; but need to catch shm and tmpfs
-	 * and ramfs pages which have been modified since creation by read
-	 * fault.
+	 * participates in dirty tracking (note that this is not only an
+	 * optimization but also solves problems caused by dirty flag in
+	 * storage key getting set by a write from inside kernel); but need to
+	 * catch shm and tmpfs and ramfs pages which have been modified since
+	 * creation by read fault.
 	 *
 	 * Note that mapping must be decided above, before decrementing
 	 * mapcount (which luckily provides a barrier): once page is unmapped,