On Fri, Jul 14, 2017 at 09:59:58AM +0200, Michal Hocko wrote: > From: Michal Hocko <mhocko@xxxxxxxx> > > 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-api@xxxxxxxxxxxxxxx> > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> > index 80e4adb4c360..d9f4ea057e74 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4864,40 +4824,22 @@ int numa_zonelist_order_handler(struct ctl_table *table, int write, > void __user *buffer, size_t *length, > loff_t *ppos) > { > - char saved_string[NUMA_ZONELIST_ORDER_LEN]; > + char *str; > int ret; > - static DEFINE_MUTEX(zl_order_mutex); > > - mutex_lock(&zl_order_mutex); > - if (write) { > - if (strlen((char *)table->data) >= NUMA_ZONELIST_ORDER_LEN) { > - ret = -EINVAL; > - goto out; > - } > - strcpy(saved_string, (char *)table->data); > + if (!write) { > + int len = sizeof("Default"); > + if (copy_to_user(buffer, "Default", len)) > + return -EFAULT; > + return len; > } That should to be "default" because the original code would have the proc entry display "default" unless it was set at runtime. Pretty weird I know but it's always possible someone is parsing the original default and not handling it properly. Otherwise I think we're way past the point where large memory 32-bit NUMA machines are a thing so Acked-by: Mel Gorman <mgorman@xxxxxxx> -- Mel Gorman SUSE Labs -- 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>