On Thu 28-09-17 14:11:41, Kemi Wang wrote: > This is the second step which introduces a tunable interface that allow > numa stats configurable for optimizing zone_statistics(), as suggested by > Dave Hansen and Ying Huang. > > ========================================================================= > When page allocation performance becomes a bottleneck and you can tolerate > some possible tool breakage and decreased numa counter precision, you can > do: > echo [C|c]oarse > /proc/sys/vm/numa_stats_mode > In this case, numa counter update is ignored. We can see about > *4.8%*(185->176) drop of cpu cycles per single page allocation and reclaim > on Jesper's page_bench01 (single thread) and *8.1%*(343->315) drop of cpu > cycles per single page allocation and reclaim on Jesper's page_bench03 (88 > threads) running on a 2-Socket Broadwell-based server (88 threads, 126G > memory). > > Benchmark link provided by Jesper D Brouer(increase loop times to > 10000000): > https://github.com/netoptimizer/prototype-kernel/tree/master/kernel/mm/ > bench > > ========================================================================= > When page allocation performance is not a bottleneck and you want all > tooling to work, you can do: > echo [S|s]trict > /proc/sys/vm/numa_stats_mode > > ========================================================================= > We recommend automatic detection of numa statistics by system, this is also > system default configuration, you can do: > echo [A|a]uto > /proc/sys/vm/numa_stats_mode > In this case, numa counter update is skipped unless it has been read by > users at least once, e.g. cat /proc/zoneinfo. I am still not convinced the auto mode is worth all the additional code and a safe default to use. The whole thing could have been 0/1 with a simpler parsing and less code to catch readers. E.g. why do we have to do static_branch_enable on any read or even vmstat_stop? Wouldn't open be sufficient? > @@ -153,6 +153,8 @@ static DEVICE_ATTR(meminfo, S_IRUGO, node_read_meminfo, NULL); > static ssize_t node_read_numastat(struct device *dev, > struct device_attribute *attr, char *buf) > { > + if (vm_numa_stats_mode == VM_NUMA_STAT_AUTO_MODE) > + static_branch_enable(&vm_numa_stats_mode_key); > return sprintf(buf, > "numa_hit %lu\n" > "numa_miss %lu\n" > @@ -186,6 +188,8 @@ static ssize_t node_read_vmstat(struct device *dev, > n += sprintf(buf+n, "%s %lu\n", > vmstat_text[i + NR_VM_ZONE_STAT_ITEMS], > sum_zone_numa_state(nid, i)); > + if (vm_numa_stats_mode == VM_NUMA_STAT_AUTO_MODE) > + static_branch_enable(&vm_numa_stats_mode_key); > #endif > > for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) [...] > @@ -1582,6 +1703,10 @@ static int zoneinfo_show(struct seq_file *m, void *arg) > { > pg_data_t *pgdat = (pg_data_t *)arg; > walk_zones_in_node(m, pgdat, false, false, zoneinfo_show_print); > +#ifdef CONFIG_NUMA > + if (vm_numa_stats_mode == VM_NUMA_STAT_AUTO_MODE) > + static_branch_enable(&vm_numa_stats_mode_key); > +#endif > return 0; > } > > @@ -1678,6 +1803,10 @@ static int vmstat_show(struct seq_file *m, void *arg) > > static void vmstat_stop(struct seq_file *m, void *arg) > { > +#ifdef CONFIG_NUMA > + if (vm_numa_stats_mode == VM_NUMA_STAT_AUTO_MODE) > + static_branch_enable(&vm_numa_stats_mode_key); > +#endif > kfree(m->private); > m->private = NULL; > } > -- > 2.7.4 > -- Michal Hocko 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>
