linux-kernel - Re: [PATCH v11 3/7] mm: introduce a common interface for balloon pages mobility

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Date:	Wed, 7 Nov 2012 13:02:07 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Rafael Aquini <aquini@...hat.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mel@....ul.ie>,
	Andi Kleen <andi@...stfloor.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Minchan Kim <minchan@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v11 3/7] mm: introduce a common interface for balloon
 pages mobility

On Wed,  7 Nov 2012 01:05:50 -0200
Rafael Aquini <aquini@...hat.com> 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)
 {

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