On Thu, Apr 01, 2021 at 09:28:03AM -0300, Jason Gunthorpe wrote: > On Thu, Apr 01, 2021 at 12:26:56PM +0100, Matthew Wilcox wrote: > > On Thu, Apr 01, 2021 at 08:05:37AM +0100, Christoph Hellwig wrote: > > > On Wed, Mar 31, 2021 at 07:47:01PM +0100, Matthew Wilcox (Oracle) wrote: > > > > - Mirror members of struct page (for pagecache / anon) into struct folio, > > > > so (eg) you can use folio->mapping instead of folio->page.mapping > > > > > > Eww, why? > > > > So that eventually we can rename page->mapping to page->_mapping and > > prevent the bugs from people doing page->mapping on a tail page. eg > > https://lore.kernel.org/linux-mm/alpine.LSU.2.11.2103102214170.7159@eggly.anvils/ > > Is that gcc structure layout randomization stuff going to be a problem > here? > > Add some > static_assert(offsetof(struct folio,..) == offsetof(struct page,..)) > > tests to force it? You sound like the kind of person who hasn't read patch 1. diff --git a/mm/util.c b/mm/util.c index 0b6dd9d81da7..521a772f06eb 100644 --- a/mm/util.c +++ b/mm/util.c @@ -686,6 +686,25 @@ struct anon_vma *page_anon_vma(struct page *page) return __page_rmapping(page); } +static inline void folio_build_bug(void) +{ +#define FOLIO_MATCH(pg, fl) \ +BUILD_BUG_ON(offsetof(struct page, pg) != offsetof(struct folio, fl)); + + FOLIO_MATCH(flags, flags); + FOLIO_MATCH(lru, lru); + FOLIO_MATCH(mapping, mapping); + FOLIO_MATCH(index, index); + FOLIO_MATCH(private, private); + FOLIO_MATCH(_mapcount, _mapcount); + FOLIO_MATCH(_refcount, _refcount); +#ifdef CONFIG_MEMCG + FOLIO_MATCH(memcg_data, memcg_data); +#endif +#undef FOLIO_MATCH + BUILD_BUG_ON(sizeof(struct page) != sizeof(struct folio)); +} + struct address_space *page_mapping(struct page *page) { struct address_space *mapping;
