Re: [PATCH v5] mm, sysctl: make NUMA stats configurable

[Vlastimil Babka]

On 10/18/2017 03:42 AM, 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 0 > /proc/sys/vm/numa_stat
> 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 1 > /proc/sys/vm/numa_stat
> This is system default setting.
> 
> Many thanks to Michal Hocko, Dave Hansen, Ying Huang and Vlastimil Babka
> for comments to help improve the original patch.
> 
> ChangeLog:
>   V4->V5
>   a) Scope vm_numa_stat_lock into the sysctl handler function, as suggested
>   by Michal Hocko;
>   b) Only allow 0/1 value when setting a value to numa_stat at userspace,
>   that would keep the possibility for add auto mode in future (e.g. 2 for
>   auto mode), as suggested by Michal Hocko.
> 
>   V3->V4
>   a) Get rid of auto mode of numa stats, and may add it back if necessary,
>   as alignment before;
>   b) Skip NUMA_INTERLEAVE_HIT counter update when numa stats is disabled,
>   as reported by Andrey Ryabinin. See commit "de55c8b2519" for details
>   c) Remove extern declaration for those clear_numa_ function, and make
>   them static in vmstat.c, as suggested by Vlastimil Babka.
> 
>   V2->V3:
>   a) Propose a better way to use jump label to eliminate the overhead of
>   branch selection in zone_statistics(), as inspired by Ying Huang;
>   b) Add a paragraph in commit log to describe the way for branch target
>   selection;
>   c) Use a more descriptive name numa_stats_mode instead of vmstat_mode,
>   and change the description accordingly, as suggested by Michal Hocko;
>   d) Make this functionality NUMA-specific via ifdef
> 
>   V1->V2:
>   a) Merge to one patch;
>   b) Use jump label to eliminate the overhead of branch selection;
>   c) Add a single-time log message at boot time to help tell users what
>   happened.
> 
> Reported-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
> Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxx>
> Suggested-by: Ying Huang <ying.huang@xxxxxxxxx>
> Signed-off-by: Kemi Wang <kemi.wang@xxxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>