A node/zone index is used to check if pages are compatible for merging
but this happens unconditionally even if the buddy page is not free. Defer
the calculation as long as possible. Ideally we would check the zone boundary
but nodes can overlap.
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
mm/page_alloc.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 88a6dac..c5933a5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -508,16 +508,26 @@ static inline int page_is_buddy(struct page *page, struct page *buddy,
if (!pfn_valid_within(page_to_pfn(buddy)))
return 0;
- if (page_zone_id(page) != page_zone_id(buddy))
- return 0;
-
if (page_is_guard(buddy) && page_order(buddy) == order) {
VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy);
+
+ if (page_zone_id(page) != page_zone_id(buddy))
+ return 0;
+
return 1;
}
if (PageBuddy(buddy) && page_order(buddy) == order) {
VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy);
+
+ /*
+ * zone check is done late to avoid uselessly
+ * calculating zone/node ids for pages that could
+ * never merge.
+ */
+ if (page_zone_id(page) != page_zone_id(buddy))
+ return 0;
+
return 1;
}
return 0;
--
1.8.4.5
--
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