On Mon, May 11, 2026 at 05:04:19AM -0400, Michael S. Tsirkin wrote: > 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 page goes through > __folio_put_zeroed() which calls free_frozen_pages_zeroed() so > the zeroed hint is preserved. 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. >
I see this gets used in mm/balloon.c not the driver itself, should these be in include/linux/mm.h or mm/internal.h ? Just wondering the utility of this being exported for drivers. > Signed-off-by: Michael S. Tsirkin <[email protected]> > Assisted-by: Claude:claude-opus-4-6 > --- > include/linux/mm.h | 12 ++++++++++++ > mm/swap.c | 18 ++++++++++++++++-- > 2 files changed, 28 insertions(+), 2 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 3b1ca90fd435..4c51b7bd7576 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 +2091,17 @@ static inline void folio_put(struct folio *folio) > __folio_put(folio); > } > > +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..8d57223dfe34 100644 > --- a/mm/swap.c > +++ b/mm/swap.c > @@ -94,7 +94,7 @@ 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) > { > if (unlikely(folio_is_zone_device(folio))) { > free_zone_device_folio(folio); > @@ -109,10 +109,24 @@ 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 >
