[PATCH RFC v2 07/18] mm: post_alloc_hook: use PG_zeroed to skip zeroing, return pghint_t

[Michael S. Tsirkin]

Add pghint_t *hints parameter to post_alloc_hook() and
prep_new_page(). post_alloc_hook() reads PageZeroed, clears
it, and returns PGHINT_ZEROED via hints.

This provides a single point where PG_zeroed is consumed and
cleared, regardless of whether the page came through PCP or
buddy. The flag is set in page_del_and_expand() and survives
both paths until post_alloc_hook() consumes it.

Only get_page_from_freelist() passes hints through
prep_new_page(); all other callers (compaction, bulk alloc,
split, contig) pass NULL.

Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: cursor-agent:GPT-5.4-xhigh
---
 mm/compaction.c |  4 ++--
 mm/internal.h   |  3 ++-
 mm/page_alloc.c | 25 +++++++++++++++++--------
 3 files changed, 21 insertions(+), 11 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 1e8f8eca318c..6fcce7756613 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -82,7 +82,7 @@ static inline bool is_via_compact_memory(int order) { return false; }
 
 static struct page *mark_allocated_noprof(struct page *page, unsigned int order, gfp_t gfp_flags)
 {
-	post_alloc_hook(page, order, __GFP_MOVABLE);
+	post_alloc_hook(page, order, __GFP_MOVABLE, NULL);
 	set_page_refcounted(page);
 	return page;
 }
@@ -1833,7 +1833,7 @@ static struct folio *compaction_alloc_noprof(struct folio *src, unsigned long da
 	}
 	dst = (struct folio *)freepage;
 
-	post_alloc_hook(&dst->page, order, __GFP_MOVABLE);
+	post_alloc_hook(&dst->page, order, __GFP_MOVABLE, NULL);
 	set_page_refcounted(&dst->page);
 	if (order)
 		prep_compound_page(&dst->page, order);
diff --git a/mm/internal.h b/mm/internal.h
index 686667b956c0..2964cdfcd31f 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -887,7 +887,8 @@ static inline void prep_compound_tail(struct page *head, int tail_idx)
 	set_page_private(p, 0);
 }
 
-void post_alloc_hook(struct page *page, unsigned int order, gfp_t gfp_flags);
+void post_alloc_hook(struct page *page, unsigned int order, gfp_t gfp_flags,
+		     pghint_t *hints);
 extern bool free_pages_prepare(struct page *page, unsigned int order);
 
 extern int user_min_free_kbytes;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ece61d02ea96..a4cfd645599a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1863,13 +1863,21 @@ static inline bool should_skip_init(gfp_t flags)
 }
 
 inline void post_alloc_hook(struct page *page, unsigned int order,
-				gfp_t gfp_flags)
+				gfp_t gfp_flags, pghint_t *hints)
 {
 	bool init = !want_init_on_free() && want_init_on_alloc(gfp_flags) &&
 			!should_skip_init(gfp_flags);
 	bool zero_tags = init && (gfp_flags & __GFP_ZEROTAGS);
+	bool zeroed = PageZeroed(page);
 	int i;
 
+	__ClearPageZeroed(page);
+	if (hints)
+		*hints = zeroed ? PGHINT_ZEROED : 0;
+
+	if (zeroed && !zero_tags)
+		init = false;
+
 	set_page_private(page, 0);
 
 	arch_alloc_page(page, order);
@@ -1918,9 +1926,9 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
 }
 
 static void prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
-							unsigned int alloc_flags)
+					unsigned int alloc_flags, pghint_t *hints)
 {
-	post_alloc_hook(page, order, gfp_flags);
+	post_alloc_hook(page, order, gfp_flags, hints);
 
 	if (order && (gfp_flags & __GFP_COMP))
 		prep_compound_page(page, order);
@@ -3991,7 +3999,8 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
 		page = rmqueue(zonelist_zone(ac->preferred_zoneref), zone, order,
 				gfp_mask, alloc_flags, ac->migratetype);
 		if (page) {
-			prep_new_page(page, order, gfp_mask, alloc_flags);
+			prep_new_page(page, order, gfp_mask, alloc_flags,
+				      hints);
 
 			/*
 			 * If this is a high-order atomic allocation then check
@@ -4227,7 +4236,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
 
 	/* Prep a captured page if available */
 	if (page)
-		prep_new_page(page, order, gfp_mask, alloc_flags);
+		prep_new_page(page, order, gfp_mask, alloc_flags, NULL);
 
 	/* Try get a page from the freelist if available */
 	if (!page)
@@ -5223,7 +5232,7 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, int preferred_nid,
 		}
 		nr_account++;
 
-		prep_new_page(page, 0, gfp, 0);
+		prep_new_page(page, 0, gfp, 0, NULL);
 		set_page_refcounted(page);
 		page_array[nr_populated++] = page;
 	}
@@ -6958,7 +6967,7 @@ static void split_free_frozen_pages(struct list_head *list, gfp_t gfp_mask)
 		list_for_each_entry_safe(page, next, &list[order], lru) {
 			int i;
 
-			post_alloc_hook(page, order, gfp_mask);
+			post_alloc_hook(page, order, gfp_mask, NULL);
 			if (!order)
 				continue;
 
@@ -7164,7 +7173,7 @@ int alloc_contig_frozen_range_noprof(unsigned long start, unsigned long end,
 		struct page *head = pfn_to_page(start);
 
 		check_new_pages(head, order);
-		prep_new_page(head, order, gfp_mask, 0);
+		prep_new_page(head, order, gfp_mask, 0, NULL);
 	} else {
 		ret = -EINVAL;
 		WARN(true, "PFN range: requested [%lu, %lu), allocated [%lu, %lu)\n",
-- 
MST