Add put_page_zeroed() / folio_put_zeroed() for callers that hold a reference to a page known to be zeroed.
If this drops the last reference, the zeroed hint is propagated to the buddy allocator. If someone else still holds a reference, the hint is simply lost - this is best-effort. This is useful for balloon drivers during deflation: the host has already zeroed the pages, and the balloon is typically the sole owner. But if the page happens to be shared, silently dropping the hint is safe and avoids the need for callers to check the refcount. Signed-off-by: Michael S. Tsirkin <[email protected]> Assisted-by: Claude:claude-opus-4-6 --- include/linux/mm.h | 13 +++++++++++++ mm/swap.c | 20 ++++++++++++++++++-- 2 files changed, 31 insertions(+), 2 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index d1e768dcda13..86638ffaad01 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1913,6 +1913,7 @@ static inline struct folio *virt_to_folio(const void *x) } void __folio_put(struct folio *folio); +void __folio_put_zeroed(struct folio *folio); void split_page(struct page *page, unsigned int order); void folio_copy(struct folio *dst, struct folio *src); @@ -2090,6 +2091,18 @@ static inline void folio_put(struct folio *folio) __folio_put(folio); } +/* Caller must be sole owner to guarantee page is still zero */ +static inline void folio_put_zeroed(struct folio *folio) +{ + if (folio_put_testzero(folio)) + __folio_put_zeroed(folio); +} + +static inline void put_page_zeroed(struct page *page) +{ + folio_put_zeroed(page_folio(page)); +} + /** * folio_put_refs - Reduce the reference count on a folio. * @folio: The folio. diff --git a/mm/swap.c b/mm/swap.c index 5cc44f0de987..ecec780172ad 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -94,13 +94,15 @@ static void page_cache_release(struct folio *folio) lruvec_unlock_irqrestore(lruvec, flags); } -void __folio_put(struct folio *folio) +static void ___folio_put(struct folio *folio, bool zeroed) { + /* zeroed hint ignored for now, no current user */ if (unlikely(folio_is_zone_device(folio))) { free_zone_device_folio(folio); return; } + /* zeroed hint ignored for now, no current user */ if (folio_test_hugetlb(folio)) { free_huge_folio(folio); return; @@ -109,10 +111,24 @@ void __folio_put(struct folio *folio) page_cache_release(folio); folio_unqueue_deferred_split(folio); mem_cgroup_uncharge(folio); - free_frozen_pages(&folio->page, folio_order(folio)); + if (zeroed) + free_frozen_pages_zeroed(&folio->page, folio_order(folio)); + else + free_frozen_pages(&folio->page, folio_order(folio)); +} + +void __folio_put(struct folio *folio) +{ + ___folio_put(folio, false); } EXPORT_SYMBOL(__folio_put); +void __folio_put_zeroed(struct folio *folio) +{ + ___folio_put(folio, true); +} +EXPORT_SYMBOL(__folio_put_zeroed); + typedef void (*move_fn_t)(struct lruvec *lruvec, struct folio *folio); static void lru_add(struct lruvec *lruvec, struct folio *folio) -- MST
