mm: add comment on storage key dirty bit semantics
Add comments that dirty bit in storage key gets set whenever page content
is changed. Hopefully if someone will use this function, he'll have a
look at one of the two places where we comment on this.
Signed-off-by: Jan Kara <jack@suse.cz>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/s390/include/asm/page.h b/arch/s390/include/asm/page.h
index 6d53670..39faa4a 100644
--- a/arch/s390/include/asm/page.h
+++ b/arch/s390/include/asm/page.h
@@ -158,6 +158,9 @@
* 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)