On Mon, Apr 13, 2026 at 09:11:51PM +0200, David Hildenbrand (Arm) wrote: > On 4/13/26 00:50, Michael S. Tsirkin wrote: > > 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 <[email protected]> > > 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 2d4b6f1a554e..edbb1edf463d 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. > > + */ > > The comment is a bit excessive. I'd say you can drop it completely. > > > + 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); > > } > > > > @@ -2322,7 +2332,8 @@ 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); > > In MM land we started doing > > /* reported= */false > > > This raises a good question: how does buddy merging handle the reported > flag? > > -- > Cheers, > > David
IIUC it doesn't: reported pages are never merged, if a page is merged it has just entered buddy. -- MST
