On Wed, Dec 05, 2018 at 12:08:20PM +0000, Wei Yang wrote: > On Wed, Dec 05, 2018 at 11:15:13AM +0000, Mel Gorman wrote: > >On Wed, Dec 05, 2018 at 05:19:04PM +0800, Wei Yang wrote: > >> When SPARSEMEM is used, there is an indication that pageblock is not > >> allowed to exceed one mem_section. Current code doesn't have this > >> constrain explicitly. > >> > >> This patch adds this to make sure it won't. > >> > >> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx> > > > >Is this even possible? This would imply that the section size is smaller > >than max order which would be quite a crazy selection for a sparesemem > >section size. A lot of assumptions on the validity of PFNs within a > >max-order boundary would be broken with such a section size. I'd be > >surprised if such a setup could even boot, let alone run. > > pageblock_order has two definitions. > > #define pageblock_order HUGETLB_PAGE_ORDER > > #define pageblock_order (MAX_ORDER-1) > > If CONFIG_HUGETLB_PAGE is not enabled, pageblock_order is related to > MAX_ORDER, which ensures it is smaller than section size. > > If CONFIG_HUGETLB_PAGE is enabled, pageblock_order is not related to > MAX_ORDER. I don't see HUGETLB_PAGE_ORDER is ensured to be less than > section size. Maybe I missed it? > HUGETLB_PAGE_ORDER is less than MAX_ORDER on the basis that normal huge pages (not gigantic) pages are served from the buddy allocator which is limited by MAX_ORDER. -- Mel Gorman SUSE Labs
