On Wed, Aug 09, 2023 at 08:07:43PM +0100, Ryan Roberts wrote: > > +++ b/mm/hugetlb.c > > @@ -1479,7 +1479,7 @@ static void __destroy_compound_gigantic_folio(struct folio *folio, > > struct page *p; > > > > atomic_set(&folio->_entire_mapcount, 0); > > - atomic_set(&folio->_nr_pages_mapped, 0); > > + atomic_set(&folio->_total_mapcount, 0); > > Just checking this is definitely what you intended? _total_mapcount is -1 when > it means "no pages mapped", so 0 means 1 page mapped? We're destroying the page here, so rather than setting the meaning of this, we're setting the contents of this memory to 0. Other thoughts that ran through my mind ... can we wrap? I don't think we can; we always increment total_mapcount by 1, no matter whether we're incrementing entire_mapcount or an individual page's mapcount, and we always call folio_get() first, so we can't increment total_mapcount past 2^32 because folio_get() will die first. We might be able to wrap past 2^31, but I don't think so. I had some other thoughts, but I convinced myself they were all OK.
