[PATCH RFC v3 11/19] mm: page_alloc: propagate PageReported flag across buddy splits

Michael S. Tsirkin
2026-04-21T22:01:55Z

When a reported free page is split via expand() to satisfy a
smaller allocation, the sub-pages placed back on the free lists
lose the PageReported flag. This means they will be unnecessarily
re-reported to the hypervisor in the next reporting cycle, wasting
work.

Propagate the PageReported flag to sub-pages during expand() so
that they are recognized as already-reported.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
mm/page_alloc.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index db2192ffc27c..211e9e32b91d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1730,7 +1730,7 @@ struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
* -- nyc
*/
static inline unsigned int expand(struct zone *zone, struct page *page, int low,
- int high, int migratetype)
+ int high, int migratetype, bool reported)
{
unsigned int size = 1 << high;
unsigned int nr_added = 0;
@@ -1752,6 +1752,15 @@ static inline unsigned int expand(struct zone *zone, struct page *page, int low,
__add_to_free_list(&page[size], zone, high, migratetype, false);
set_buddy_order(&page[size], high);
nr_added += size;
+
+ /*
+ * The parent page has been reported to the host. The
+ * sub-pages are part of the same reported block, so mark
+ * them reported too. This avoids re-reporting pages that
+ * the host already knows about.
+ */
+ if (reported)
+ __SetPageReported(&page[size]);
}

return nr_added;
@@ -1762,9 +1771,10 @@ static __always_inline void page_del_and_expand(struct zone *zone,
int high, int migratetype)
{
int nr_pages = 1 << high;
+ bool was_reported = page_reported(page);

__del_page_from_free_list(page, zone, high, migratetype);
- nr_pages -= expand(zone, page, low, high, migratetype);
+ nr_pages -= expand(zone, page, low, high, migratetype, was_reported);
account_freepages(zone, -nr_pages, migratetype);
}

@@ -2334,7 +2344,8 @@ try_to_claim_block(struct zone *zone, struct page *page,

del_page_from_free_list(page, zone, current_order, block_type);
change_pageblock_range(page, current_order, start_type);
- nr_added = expand(zone, page, order, current_order, start_type);
+ nr_added = expand(zone, page, order, current_order, start_type,
+ false);
account_freepages(zone, nr_added, start_type);
return page;
}
--
MST