[PATCH 07/10] Add page_is_buddy for recent kernels

[HATAYAMA Daisuke]

On kernels from v2.6.38 and later kernels, buddy page is marked by
_mapcount == PAGE_BUDDY_MAPCOUNT_VALUE, which varies once as follows:

  kernel version    | PAGE_BUDDY_MAPCOUNT_VALUE
  ------------------+--------------------------
  v2.6.38           | -2
  v2.6.39 and later | -128

One more notice is that _mapcount shares its memory with other fields
for SLAB/SLUB when PG_slab is set. Before looking up _mapcount value,
we need to check if PG_slab is set.

Signed-off-by: HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com>
---

 makedumpfile.c |   25 +++++++++++++++++++++++--
 1 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/makedumpfile.c b/makedumpfile.c
index 6358fc0..27ad3e6 100644
--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -3642,11 +3642,32 @@ exclude_free_page(void)
 	return TRUE;
 }
 
+/*
+ * For v2.6.38 and later kernel versions.
+ */
+static int
+page_is_buddy_v3(unsigned long flags, unsigned int _mapcount,
+			unsigned long private, unsigned int _count)
+{
+	if (flags & (1UL << NUMBER(PG_slab)))
+		return FALSE;
+
+	if (_mapcount == (int)NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE))
+		return TRUE;
+
+	return FALSE;
+}
+
 static void
 setup_page_is_buddy(void)
 {
-	MSG("Can't select page_is_buddy handler; "
-	    "filtering free pages is disabled.\n");
+	if (NUMBER(PG_buddy) == NOT_FOUND_NUMBER
+	    && SIZE(pageflags) != NOT_FOUND_STRUCTURE
+	    && NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE) != NOT_FOUND_NUMBER)
+		info->page_is_buddy = page_is_buddy_v3;
+	else
+		MSG("Can't select page_is_buddy handler; "
+		    "filtering free pages is disabled.\n");
 }
 
 /*