On Wed,  7 Nov 2012 01:05:50 -0200
Rafael Aquini [off-list ref] wrote:

Memory fragmentation introduced by ballooning might reduce significantly
the number of 2MB contiguous memory blocks that can be used within a guest,
thus imposing performance penalties associated with the reduced number of
transparent huge pages that could be used by the guest workload.

This patch introduces a common interface to help a balloon driver on
making its page set movable to compaction, and thus allowing the system
to better leverage the compation efforts on memory defragmentation.

mm/migrate.c: In function 'unmap_and_move':
mm/migrate.c:899: error: 'COMPACTBALLOONRELEASED' undeclared (first use in this function)
mm/migrate.c:899: error: (Each undeclared identifier is reported only once
mm/migrate.c:899: error: for each function it appears in.)

You've been bad - you didn't test with your feature disabled. 
Please do that.  And not just compilation testing.


We can fix this one with a sucky macro.  I think that's better than
unconditionally defining the enums.

--- a/include/linux/balloon_compaction.h~mm-introduce-a-common-interface-for-balloon-pages-mobility-fix
+++ a/include/linux/balloon_compaction.h

@@ -207,10 +207,8 @@ static inline gfp_t balloon_mapping_gfp_
 	return GFP_HIGHUSER;
 }
 
-static inline void balloon_event_count(enum vm_event_item item)
-{
-	return;
-}
+/* A macro, to avoid generating references to the undefined COMPACTBALLOON* */
+#define balloon_event_count(item) do { } while (0)
 
 static inline bool balloon_compaction_check(void)
 {