PM/Hibernate: do not count debug pages as savable

When debugging with CONFIG_DEBUG_PAGEALLOC and debug_guardpage_minorder >
0, we have lot of free pages that are not marked so.  Snapshot code
account them as savable, what cause hibernate memory preallocation
failure.

It is pretty hard to make hibernate allocation succeed with
debug_guardpage_minorder=1.  This change at least make it possible when
system has relatively big amount of RAM.

Signed-off-by: Stanislaw Gruszka <[email protected]>
Acked-by: Rafael J. Wysocki <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Pekka Enberg <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

kernel/power/snapshot.c

@@ -858,6 +858,9 @@ static struct page *saveable_highmem_page(struct zone *zone, unsigned long pfn)
 	    PageReserved(page))
 		return NULL;
 
+	if (page_is_guard(page))
+		return NULL;
+
 	return page;
 }
 
@@ -920,6 +923,9 @@ static struct page *saveable_page(struct zone *zone, unsigned long pfn)
 	    && (!kernel_page_present(page) || pfn_is_nosave(pfn)))
 		return NULL;
 
+	if (page_is_guard(page))
+		return NULL;
+
 	return page;
 }