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; "
