On Wed, Dec 05, 2018 at 03:37:33PM +0000, Mel Gorman wrote: >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. > Maybe I am lost here, I got one possible definition on x86. #define pageblock_order HUGETLB_PAGE_ORDER #define HUGETLB_PAGE_ORDER (HPAGE_SHIFT - PAGE_SHIFT) #define HPAGE_SHIFT PMD_SHIFT #define PMD_SHIFT PUD_SHIFT #define PUD_SHIFT 30 This leads to pageblock_order = (30 - 12) = 18 > MAX_ORDER ? What you mentioned sounds reasonable. A huge page should be less than MAX_ORDER, otherwise page allocator couldn't handle it. But I don't see the connection between MAX_ORDER and HUGETLB_PAGE_ORDER. Do we need to add a check on this? Or it already has similar contrain in code, but I missed it? >-- >Mel Gorman >SUSE Labs -- Wei Yang Help you, Help me
