[PATCH RFC v2 17/18] mm: add free_frozen_pages_hint and put_page_hint APIs

["Michael S. Tsirkin" <mst@redhat.com>]

Add free_frozen_pages_hint(page, order, hints) to free a page
while marking it as pre-zeroed when PGHINT_ZEROED is set.
The PG_zeroed flag is set after __free_pages_prepare so it
survives on the free list.

Add __folio_put_hint(), folio_put_hint(), and put_page_hint()
wrappers for the put_page path.

These APIs are intended for balloon drivers during deflation
when the host has zeroed the pages.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 include/linux/gfp.h |  2 ++
 include/linux/mm.h  | 12 ++++++++++++
 mm/page_alloc.c     | 21 +++++++++++++++------
 mm/swap.c           | 19 +++++++++++++++++++
 4 files changed, 48 insertions(+), 6 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 14433a20e60c..b226d5e1930e 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -404,6 +404,8 @@ __meminit void *alloc_pages_exact_nid_noprof(int nid, size_t size, gfp_t gfp_mas
 extern void __free_pages(struct page *page, unsigned int order);
 extern void free_pages_nolock(struct page *page, unsigned int order);
 extern void free_pages(unsigned long addr, unsigned int order);
+void free_frozen_pages_hint(struct page *page, unsigned int order,
+			    pghint_t hints);
 
 #define __free_page(page) __free_pages((page), 0)
 #define free_page(addr) free_pages((addr), 0)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index abb4963c1f06..f4e28c55e2c9 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1640,6 +1640,7 @@ static inline struct folio *virt_to_folio(const void *x)
 }
 
 void __folio_put(struct folio *folio);
+void __folio_put_hint(struct folio *folio, pghint_t hints);
 
 void split_page(struct page *page, unsigned int order);
 void folio_copy(struct folio *dst, struct folio *src);
@@ -1817,6 +1818,17 @@ static inline void folio_put(struct folio *folio)
 		__folio_put(folio);
 }
 
+static inline void folio_put_hint(struct folio *folio, pghint_t hints)
+{
+	if (folio_put_testzero(folio))
+		__folio_put_hint(folio, hints);
+}
+
+static inline void put_page_hint(struct page *page, pghint_t hints)
+{
+	folio_put_hint(page_folio(page), hints);
+}
+
 /**
  * folio_put_refs - Reduce the reference count on a folio.
  * @folio: The folio.
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a4cfd645599a..f04813db3015 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3000,7 +3000,7 @@ static bool free_frozen_page_commit(struct zone *zone,
  * Free a pcp page
  */
 static void __free_frozen_pages(struct page *page, unsigned int order,
-				fpi_t fpi_flags)
+				fpi_t fpi_flags, pghint_t hints)
 {
 	unsigned long UP_flags;
 	struct per_cpu_pages *pcp;
@@ -3016,6 +3016,9 @@ static void __free_frozen_pages(struct page *page, unsigned int order,
 	if (!__free_pages_prepare(page, order, fpi_flags))
 		return;
 
+	if (hints & PGHINT_ZEROED)
+		__SetPageZeroed(page);
+
 	/*
 	 * We only track unmovable, reclaimable and movable on pcp lists.
 	 * Place ISOLATE pages on the isolated list because they are being
@@ -3051,12 +3054,18 @@ static void __free_frozen_pages(struct page *page, unsigned int order,
 
 void free_frozen_pages(struct page *page, unsigned int order)
 {
-	__free_frozen_pages(page, order, FPI_NONE);
+	__free_frozen_pages(page, order, FPI_NONE, 0);
+}
+
+void free_frozen_pages_hint(struct page *page, unsigned int order,
+			    pghint_t hints)
+{
+	__free_frozen_pages(page, order, FPI_NONE, hints);
 }
 
 void free_frozen_pages_nolock(struct page *page, unsigned int order)
 {
-	__free_frozen_pages(page, order, FPI_TRYLOCK);
+	__free_frozen_pages(page, order, FPI_TRYLOCK, 0);
 }
 
 /*
@@ -5385,7 +5394,7 @@ static void ___free_pages(struct page *page, unsigned int order,
 	struct alloc_tag *tag = pgalloc_tag_get(page);
 
 	if (put_page_testzero(page))
-		__free_frozen_pages(page, order, fpi_flags);
+		__free_frozen_pages(page, order, fpi_flags, 0);
 	else if (!head) {
 		pgalloc_tag_sub_pages(tag, (1 << order) - 1);
 		while (order-- > 0) {
@@ -5396,7 +5405,7 @@ static void ___free_pages(struct page *page, unsigned int order,
 			 */
 			clear_page_tag_ref(page + (1 << order));
 			__free_frozen_pages(page + (1 << order), order,
-					    fpi_flags);
+					    fpi_flags, 0);
 		}
 	}
 }
@@ -7879,7 +7888,7 @@ struct page *alloc_frozen_pages_nolock_noprof(gfp_t gfp_flags, int nid, unsigned
 
 	if (memcg_kmem_online() && page && (gfp_flags & __GFP_ACCOUNT) &&
 	    unlikely(__memcg_kmem_charge_page(page, alloc_gfp, order) != 0)) {
-		__free_frozen_pages(page, order, FPI_TRYLOCK);
+		__free_frozen_pages(page, order, FPI_TRYLOCK, 0);
 		page = NULL;
 	}
 	trace_mm_page_alloc(page, order, alloc_gfp, ac.migratetype);
diff --git a/mm/swap.c b/mm/swap.c
index bb19ccbece46..1dfd232d3944 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -113,6 +113,25 @@ void __folio_put(struct folio *folio)
 }
 EXPORT_SYMBOL(__folio_put);
 
+void __folio_put_hint(struct folio *folio, pghint_t hints)
+{
+	if (unlikely(folio_is_zone_device(folio))) {
+		free_zone_device_folio(folio);
+		return;
+	}
+
+	if (folio_test_hugetlb(folio)) {
+		free_huge_folio(folio);
+		return;
+	}
+
+	page_cache_release(folio);
+	folio_unqueue_deferred_split(folio);
+	mem_cgroup_uncharge(folio);
+	free_frozen_pages_hint(&folio->page, folio_order(folio), hints);
+}
+EXPORT_SYMBOL(__folio_put_hint);
+
 typedef void (*move_fn_t)(struct lruvec *lruvec, struct folio *folio);
 
 static void lru_add(struct lruvec *lruvec, struct folio *folio)
-- 
MST