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.
While I was unable to quantify the performance difference, it is an obvious waste, even if small. Propagate the PageReported flag to sub-pages during expand(), both in page_del_and_expand() and try_to_claim_block(), so split_large_buddy() also propagates PageReported via a bool parameter: the caller saves PageReported before del_page_from_free_list() clears it, then passes the saved value. The flag is set after __free_one_page() with a PageBuddy check, matching the page_reporting_drain() pattern. Free-path callers pass false (freshly freed pages are never reported). 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 | 32 +++++++++++++++++++++++++------- 1 file changed, 25 insertions(+), 7 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index d49c254174da..8dae5b3f5876 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1502,7 +1502,8 @@ static void free_pcppages_bulk(struct zone *zone, int count, /* Split a multi-block free page into its individual pageblocks. */ static void split_large_buddy(struct zone *zone, struct page *page, - unsigned long pfn, int order, fpi_t fpi) + unsigned long pfn, int order, fpi_t fpi, + bool reported) { unsigned long end = pfn + (1 << order); @@ -1517,6 +1518,8 @@ static void split_large_buddy(struct zone *zone, struct page *page, int mt = get_pfnblock_migratetype(page, pfn); __free_one_page(page, pfn, zone, order, mt, fpi); + if (reported && PageBuddy(page) && buddy_order(page) == order) + __SetPageReported(page); pfn += 1 << order; if (pfn == end) break; @@ -1559,11 +1562,12 @@ static void free_one_page(struct zone *zone, struct page *page, llist_for_each_entry_safe(p, tmp, llnode, pcp_llist) { unsigned int p_order = p->private; - split_large_buddy(zone, p, page_to_pfn(p), p_order, fpi_flags); + split_large_buddy(zone, p, page_to_pfn(p), p_order, + fpi_flags, false); __count_vm_events(PGFREE, 1 << p_order); } } - split_large_buddy(zone, page, pfn, order, fpi_flags); + split_large_buddy(zone, page, pfn, order, fpi_flags, false); spin_unlock_irqrestore(&zone->lock, flags); __count_vm_events(PGFREE, 1 << order); @@ -1694,7 +1698,7 @@ 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; @@ -1716,6 +1720,15 @@ 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; @@ -1726,9 +1739,10 @@ 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); } @@ -2116,11 +2130,13 @@ static bool __move_freepages_block_isolate(struct zone *zone, /* We're a part of a larger buddy */ if (PageBuddy(buddy) && buddy_order(buddy) > pageblock_order) { int order = buddy_order(buddy); + bool reported = PageReported(buddy); del_page_from_free_list(buddy, zone, order, get_pfnblock_migratetype(buddy, buddy_pfn)); toggle_pageblock_isolate(page, isolate); - split_large_buddy(zone, buddy, buddy_pfn, order, FPI_NONE); + split_large_buddy(zone, buddy, buddy_pfn, order, FPI_NONE, + reported); return true; } @@ -2283,10 +2299,12 @@ try_to_claim_block(struct zone *zone, struct page *page, /* Take ownership for orders >= pageblock_order */ if (current_order >= pageblock_order) { unsigned int nr_added; + bool was_reported = page_reported(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, + was_reported); account_freepages(zone, nr_added, start_type); return page; } -- MST
