On 12/2/20 1:21 PM, Muchun Song wrote:
> The max order page has no buddy page and never merge to other order.
> So isolating and then freeing it is pointless.
>
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
> mm/page_isolation.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index a254e1f370a3..bddf788f45bf 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -88,7 +88,7 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
> */
> if (PageBuddy(page)) {
> order = buddy_order(page);
> - if (order >= pageblock_order) {
> + if (order >= pageblock_order && order < MAX_ORDER - 1) {
> pfn = page_to_pfn(page);
> buddy_pfn = __find_buddy_pfn(pfn, order);
> buddy = page + (buddy_pfn - pfn);
Hm I wonder if order == MAX_ORDER - 1, then the buddy can actually be a
!pfn_valid() in some corner case? pfn_valid_within(buddy_pfn) that follows would
only catch it on archs with holes in zone. Then is_migrate_isolate_page(buddy)
might access an invalid buddy. So this might be actually a bug fix and not just
optimization, just the bug hasn't been observed in practice.
>
