From: Andy Whitcroft Currently if we have a non-zero ZONES_SHIFT we assume we are able to rely on that as the bottom edge of the ZONEID, if not then we use the NODES_PGOFF as the right end of either NODES _or_ SECTION. This latter is more luck than judgement and would be incorrect if we reordered the SECTION,NODE,ZONE options in the fields space. Really what we want is the lower of the right hand end of the two fields we are using (either NODE,ZONE or SECTION,ZONE). Codify that explicitly. As always allow for there being no bits in either of the fields, such as might be valid in a non-numa machine with only a zone NORMAL. I have checked that the compiler is still able to constant fold all of this away correctly. Signed-off-by: Andy Whitcroft Acked-by: Christoph Lameter Signed-off-by: Andrew Morton --- include/linux/mm.h | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff -puN include/linux/mm.h~zoneid-fix-up-calculations-for-zoneid_pgshift include/linux/mm.h --- a/include/linux/mm.h~zoneid-fix-up-calculations-for-zoneid_pgshift +++ a/include/linux/mm.h @@ -416,15 +416,15 @@ void split_page(struct page *page, unsig /* NODE:ZONE or SECTION:ZONE is used to ID a zone for the buddy allcator */ #ifdef NODE_NOT_IN_PAGEFLAGS #define ZONEID_SHIFT (SECTIONS_SHIFT + ZONES_SHIFT) +#define ZONEID_PGOFF ((SECTIONS_PGOFF < ZONES_PGOFF)? \ + SECTIONS_PGOFF : ZONES_PGOFF) #else #define ZONEID_SHIFT (NODES_SHIFT + ZONES_SHIFT) +#define ZONEID_PGOFF ((NODES_PGOFF < ZONES_PGOFF)? \ + NODES_PGOFF : ZONES_PGOFF) #endif -#if ZONES_WIDTH > 0 -#define ZONEID_PGSHIFT ZONES_PGSHIFT -#else -#define ZONEID_PGSHIFT NODES_PGOFF -#endif +#define ZONEID_PGSHIFT (ZONEID_PGOFF * (ZONEID_SHIFT != 0)) #if SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH > FLAGS_RESERVED #error SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH > FLAGS_RESERVED @@ -450,7 +450,6 @@ static inline enum zone_type page_zonenu */ static inline int page_zone_id(struct page *page) { - BUILD_BUG_ON(ZONEID_PGSHIFT == 0 && ZONEID_MASK); return (page->flags >> ZONEID_PGSHIFT) & ZONEID_MASK; } _