On Thu, Dec 06, 2018 at 10:00:05AM +0100, David Hildenbrand wrote: >On 05.12.18 23:31, Wei Yang wrote: >> 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 > >PMD_SHIFT is usually 21 > >arch/x86/include/asm/pgtable-3level_types.h:#define PMD_SHIFT 21 >arch/x86/include/asm/pgtable_64_types.h:#define PMD_SHIFT 21 > >Unless CONFIG_PGTABLE_LEVELS <= 2 > >Then include/asm-generic/pgtable-nopmd.h will be used in >arch/x86/include/asm/pgtable_types.h > #define PMD_SHIFT PUD_SHIFT > >In that case, also include/asm-generic/pgtable-nopmd.h is uses > #define PUD_SHIFT P4D_SHIFT > >... include/asm-generic/pgtable-nop4d.h > #define P4D_SHIFT PGDIR_SHIFT > > >And that would be >arch/x86/include/asm/pgtable-2level_types.h:#define PGDIR_SHIFT 22 > >If I am not wrong. > >So we would have pageblock_order = (22 - 12) = 10 > Thank, David :-) I think current configuration is correct, while all these digits are written by programmer. My concern and suggestion is to add a compiler check to enforce this. So that we would avoid this situation if someone miss this constrain. Just as the check on MAX_ORDER and SECION_SIZE. > >> #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 >> > > >-- > >Thanks, > >David / dhildenb -- Wei Yang Help you, Help me
