Messages in this thread | | | From | Muchun Song <> | Date | Thu, 3 Dec 2020 10:43:29 +0800 | Subject | Re: [External] Re: [PATCH] mm/page_isolation: do not isolate the max order page |
| |
On Thu, Dec 3, 2020 at 8:03 AM Vlastimil Babka <vbabka@suse.cz> wrote: > > 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@bytedance.com> > > Acked-by: Vlastimil Babka <vbabka@suse.cz> > > > --- > > 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.
Agree. Should we add a Fixes tag in the commit log? Thanks.
> > > >
-- Yours, Muchun
| |