On Thu, Jun 15, 2023 at 09:15:26PM +0100, Matthew Wilcox wrote: > On Thu, Jun 15, 2023 at 03:33:12PM -0400, Peter Xu wrote: > > My question is whether page_zonenum() is ready for taking all kinds of tail > > pages? > > > > Zone device tail pages all look fine, per memmap_init_zone_device(). The > > question was other kinds of usual compound pages, like either thp or > > hugetlb. IIUC page->flags can be uninitialized for those tail pages. > > I don't think that's true. It's my understanding that page->flags is > initialised for all pages in memmap at boot / hotplug / delayed-init > time. So you can check things like zone, node, etc on literally any > page. Contrariwise, those flags are not available in tail pages for > use by the entity that has allocated a compound page / large folio. Oh so the zone mask is special. Fair enough. > > Also, I don't believe zone device pages support compound allocation. > I think they're always allocated as order-0. Totally not familiar with zone device pages, but memmap_init_zone_device() has pfns_per_compound which can be >1. From there, memmap_init_compound() does go ahead and setup pages as compound ones. Thanks! -- Peter Xu
