From: Eric Dumazet <edumazet@xxxxxxxxxx>
Grabbing zone lock in is_free_buddy_page() gives a wrong sense of safety,
and has potential performance implications when zone is experiencing
lock contention.
In any case, if a caller needs a stable result, it should grab zone
lock before calling this function.
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
---
mm/page_alloc.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e115e21524739341d409b28379942241ed403060..cd8a72372b047e55c4cde80fe6b7a428d7721027 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -9354,21 +9354,21 @@ void __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
}
#endif
+/*
+ * This function returns a stable result only if called under zone lock.
+ */
bool is_free_buddy_page(struct page *page)
{
- struct zone *zone = page_zone(page);
unsigned long pfn = page_to_pfn(page);
- unsigned long flags;
unsigned int order;
- spin_lock_irqsave(&zone->lock, flags);
for (order = 0; order < MAX_ORDER; order++) {
struct page *page_head = page - (pfn & ((1 << order) - 1));
- if (PageBuddy(page_head) && buddy_order(page_head) >= order)
+ if (PageBuddy(page_head) &&
+ buddy_order_unsafe(page_head) >= order)
break;
}
- spin_unlock_irqrestore(&zone->lock, flags);
return order < MAX_ORDER;
}
--
2.33.0.464.g1972c5931b-goog
