[RFC PATCH 09/10] Add page_is_buddy for PG_buddy

[HATAYAMA Daisuke]

On kernels from v2.6.18 to v2.6.37, buddy page is marked by the
PG_buddy flag.

  kernel version     | PG_buddy
  ------------------ +---------------------------------
  v2.6.17 to v2.6.26 | 19
  v2.6.27 to v2.6.37 | 19 if CONFIG_PAGEFLAGS_EXTEND=y
                     | 18 otherwise

Note for hard coding: it's possible to determine whether
CONFIG_PAGEFLAGS_EXTEND=yes or not by looking at error_status array
defined in mm/memory-failure.c, for example.

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

 makedumpfile.c |   27 ++++++++++++++++++++-------
 1 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/makedumpfile.c b/makedumpfile.c
index aea956f..675b47e 100644
--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -3518,6 +3518,16 @@ exclude_free_page(void)
 }
 
 static int
+page_is_buddy_v2(unsigned long flags, unsigned int _mapcount,
+		 unsigned long private, unsigned int _count)
+{
+	if (flags & (1UL << NUMBER(PG_buddy)))
+		return TRUE;
+
+	return FALSE;
+}
+
+static int
 page_is_buddy_v3(unsigned long flags, unsigned int _mapcount,
 		 unsigned long private, unsigned int _count)
 {
@@ -3533,13 +3543,16 @@ page_is_buddy_v3(unsigned long flags, unsigned int _mapcount,
 static void
 setup_page_is_buddy(void)
 {
-	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;
-
-	MSG("Can't select page_is_buddy handler; "
-	    "filtering free pages is disabled.\n");
+	if (NUMBER(PG_buddy) == NOT_FOUND_NUMBER) {
+		if (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");
+		}
+	} else
+		info->page_is_buddy = page_is_buddy_v2;
 }
 
 /*