[PATCH v2 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.

Since this page_is_buddy needs _mapcount, we use freelist logic if
_mapcount is not available.

Recall that PG_slab has been 7 since v2.6.15. No need to check it.

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

 makedumpfile.c |   21 +++++++++++++++++++++
 1 files changed, 21 insertions(+), 0 deletions(-)

diff --git a/makedumpfile.c b/makedumpfile.c
index 0e44a8b..7b13dca 100644
--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -3668,12 +3668,33 @@ 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)
 {
 	if (OFFSET(page.private) == NOT_FOUND_STRUCTURE)
 		goto out;
 
+	if (NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE) != NOT_FOUND_NUMBER) {
+		if (OFFSET(page._mapcount) != NOT_FOUND_STRUCTURE)
+			info->page_is_buddy = page_is_buddy_v3;
+	}
+
 out:
 	if (!info->page_is_buddy)
 		DEBUG_MSG("Can't select page_is_buddy handler; "