On 07/14/2017 09:59 AM, Michal Hocko wrote: > From: Michal Hocko <mho...@suse.com> > > Supporting zone ordered zonelists costs us just a lot of code while > the usefulness is arguable if existent at all. Mel has already made > node ordering default on 64b systems. 32b systems are still using > ZONELIST_ORDER_ZONE because it is considered better to fallback to > a different NUMA node rather than consume precious lowmem zones. > > This argument is, however, weaken by the fact that the memory reclaim > has been reworked to be node rather than zone oriented. This means > that lowmem requests have to skip over all highmem pages on LRUs already > and so zone ordering doesn't save the reclaim time much. So the only > advantage of the zone ordering is under a light memory pressure when > highmem requests do not ever hit into lowmem zones and the lowmem > pressure doesn't need to reclaim. > > Considering that 32b NUMA systems are rather suboptimal already and > it is generally advisable to use 64b kernel on such a HW I believe we > should rather care about the code maintainability and just get rid of > ZONELIST_ORDER_ZONE altogether. Keep systcl in place and warn if > somebody tries to set zone ordering either from kernel command line > or the sysctl. > > Cc: <linux-...@vger.kernel.org> > Signed-off-by: Michal Hocko <mho...@suse.com>
Found some leftovers to cleanup: include/linux/mmzone.h: extern char numa_zonelist_order[]; #define NUMA_ZONELIST_ORDER_LEN 16 /* string buffer size */ Also update docs? Documentation/sysctl/vm.txt:zone. Specify "[Zz]one" for zone order. Documentation/admin-guide/kernel-parameters.txt: numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. Documentation/vm/numa:a default zonelist order based on the sizes of the various zone types relative Documentation/vm/numa:default zonelist order may be overridden using the numa_zonelist_order kernel Otherwise, Acked-by: Vlastimil Babka <vba...@suse.cz>
