Re: [PATCH] compaction: fix build error in CMA && !COMPACTION

On Thu, Dec 20, 2012 at 10:47:07AM +0000, Mel Gorman wrote:

On Thu, Dec 20, 2012 at 02:25:30PM +0900, Minchan Kim wrote:

quoted

isolate_freepages_block and isolate_migratepages_range is used for CMA
as well as compaction so it breaks build for CONFIG_CMA &&
!CONFIG_COMPACTION.

This patch fixes it.

Cc: Mel Gorman <mgorman@suse.de>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 mm/compaction.c |   26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 5ad7f4f..70f4443 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c

@@ -17,6 +17,21 @@
 #include <linux/balloon_compaction.h>
 #include "internal.h"
 
+#ifdef CONFIG_COMPACTION
+static inline void count_compact_event(enum vm_event_item item)
+{
+	count_vm_event(item);
+}
+
+static inline void count_compact_events(enum vm_event_item item, long delta)
+{
+	count_vm_events(item, delta);
+}
+#else
+#define count_compact_event(item)
+#define count_compact_events(item, delta)
+#endif
+

That should be

do {} while (0)

otherwise a block like this

if (foo)
	count_compact_event(COMPACTFREE_SCANNED)
bar;

will get parsed as

if (foo)
	bar;

which is wrong.

Indeed.

Now that I look at the do {} while (0) thing it is also strictly speaking
wrong for count_vm_numa_events() too because it would do the wrong thing for

If I noticed it, I should named it as count_vm_compact_events for the consistency.

count_compact_events(COMPACTFREE_SCANNED, foo++);

There happens to be no examples where we depend on such side-effects but

Agreed.

I've taken a TODO item to fix it up in the New Year.

Andrew picked up the patch with your fix. Please correct it for New Year's
present. :)

Thanks, Mel.

-- 
Mel Gorman
SUSE Labs

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-- 
Kind regards,
Minchan Kim

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