From: Andy Whitcroft Generally we work under the assumption that memory the mem_map array is contigious and valid out to MAX_ORDER_NR_PAGES block of pages, ie. that if we have validated any page within this MAX_ORDER_NR_PAGES block we need not check any other. This is not true when CONFIG_HOLES_IN_ZONE is set and we must check each and every reference we make from a pfn. Add a pfn_valid_within() helper which should be used when scanning pages within a MAX_ORDER_NR_PAGES block when we have already checked the validility of the block normally with pfn_valid(). This can then be optimised away when we do not have holes within a MAX_ORDER_NR_PAGES block of pages. Signed-off-by: Andy Whitcroft Acked-by: Mel Gorman Acked-by: Bob Picco Signed-off-by: Andrew Morton --- include/linux/mmzone.h | 12 ++++++++++++ mm/page_alloc.c | 8 ++------ 2 files changed, 14 insertions(+), 6 deletions(-) diff -puN include/linux/mmzone.h~add-pfn_valid_within-helper-for-sub-max_order-hole-detection include/linux/mmzone.h --- a/include/linux/mmzone.h~add-pfn_valid_within-helper-for-sub-max_order-hole-detection +++ a/include/linux/mmzone.h @@ -832,6 +832,18 @@ void sparse_init(void); void memory_present(int nid, unsigned long start, unsigned long end); unsigned long __init node_memmap_size_bytes(int, unsigned long, unsigned long); +/* + * If it is possible to have holes within a MAX_ORDER_NR_PAGES, then we + * need to check pfn validility within that MAX_ORDER_NR_PAGES block. + * pfn_valid_within() should be used in this case; we optimise this away + * when we have no holes within a MAX_ORDER_NR_PAGES block. + */ +#ifdef CONFIG_HOLES_IN_ZONE +#define pfn_valid_within(pfn) pfn_valid(pfn) +#else +#define pfn_valid_within(pfn) (1) +#endif + #endif /* !__ASSEMBLY__ */ #endif /* __KERNEL__ */ #endif /* _LINUX_MMZONE_H */ diff -puN mm/page_alloc.c~add-pfn_valid_within-helper-for-sub-max_order-hole-detection mm/page_alloc.c --- a/mm/page_alloc.c~add-pfn_valid_within-helper-for-sub-max_order-hole-detection +++ a/mm/page_alloc.c @@ -206,10 +206,8 @@ static int page_outside_zone_boundaries( static int page_is_consistent(struct zone *zone, struct page *page) { -#ifdef CONFIG_HOLES_IN_ZONE - if (!pfn_valid(page_to_pfn(page))) + if (!pfn_valid_within(page_to_pfn(page))) return 0; -#endif if (zone != page_zone(page)) return 0; @@ -396,10 +394,8 @@ __find_combined_index(unsigned long page static inline int page_is_buddy(struct page *page, struct page *buddy, int order) { -#ifdef CONFIG_HOLES_IN_ZONE - if (!pfn_valid(page_to_pfn(buddy))) + if (!pfn_valid_within(page_to_pfn(buddy))) return 0; -#endif if (page_zone_id(page) != page_zone_id(buddy)) return 0; _