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 <[email protected]> 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
