[RFC PATCH 08/10] Add page_is_buddy for recent kernels

[HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>]

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. We need to check if PG_slab is set
or not before looking up _mapcount value.

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

 makedumpfile.c |   30 ++++++++++++++++++++++++++++++
 1 files changed, 30 insertions(+), 0 deletions(-)

diff --git a/makedumpfile.c b/makedumpfile.c
index 37c371e..aea956f 100644
--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -55,6 +55,8 @@ do { \
 		*ptr_long_table = value; \
 } while (0)
 
+static void setup_page_is_buddy(void);
+
 void
 initialize_tables(void)
 {
@@ -2733,6 +2735,9 @@ out:
 	if (!get_value_for_old_linux())
 		return FALSE;
 
+	if (info->dump_level & DL_EXCLUDE_FREE_CONST)
+		setup_page_is_buddy();
+
 	return TRUE;
 }
 
@@ -3512,6 +3517,31 @@ exclude_free_page(void)
 	return TRUE;
 }
 
+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 (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 using a dumpfile in kdump-compressed format as a source file
  * instead of /proc/vmcore, 1st-bitmap of a new dumpfile must be


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