On Mon, 21 Dec 2015, Joonsoo Kim wrote: > free_pfn and compact_cached_free_pfn are the pointer that remember > restart position of freepage scanner. When they are reset or invalid, > we set them to zone_end_pfn because freepage scanner works in reverse > direction. But, because zone range is defined as [zone_start_pfn, > zone_end_pfn), zone_end_pfn is invalid to access. Therefore, we should > not store it to free_pfn and compact_cached_free_pfn. Instead, we need > to store zone_end_pfn - 1 to them. There is one more thing we should > consider. Freepage scanner scan reversely by pageblock unit. If free_pfn > and compact_cached_free_pfn are set to middle of pageblock, it regards > that sitiation as that it already scans front part of pageblock so we > lose opportunity to scan there. To fix-up, this patch do round_down() > to guarantee that reset position will be pageblock aligned. > > Note that thanks to the current pageblock_pfn_to_page() implementation, > actual access to zone_end_pfn doesn't happen until now. But, following > patch will change pageblock_pfn_to_page() so this patch is needed > from now on. > > Acked-by: Vlastimil Babka <vbabka@xxxxxxx> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Acked-by: David Rientjes <rientjes@xxxxxxxxxx> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>