In __free_pages_prepare(), when FPI_ZEROED is set the page is already
known to be zero. We can skip kernel_init_pages() if page poisoning is
not enabled (because poison would overwrite the zeroes).
This avoids redundant zeroing work when freeing pages that are already
known to contain all zeros.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
mm/page_alloc.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 399e2038dcd9..90a92be96ebf 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1447,7 +1447,14 @@ __always_inline bool __free_pages_prepare(struct page *page,
if (kasan_has_integrated_init())
init = false;
}
- if (init)
+ /*
+ * Skip redundant zeroing when the page is already known-zero
+ * (FPI_ZEROED) and page poisoning did not overwrite it.
+ * When page_poisoning is enabled, kernel_poison_pages above
+ * wrote PAGE_POISON (0xAA), so we must re-zero.
+ */
+ if (init && !((fpi_flags & FPI_ZEROED) &&
+ !page_poisoning_enabled_static()))
kernel_init_pages(page, 1 << order);
/*
--
MST