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

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 <redacted>
Suggested-by: Dave Hansen <redacted>
Suggested-by: Ying Huang <redacted>
Signed-off-by: Kemi Wang <redacted>

Acked-by: Vlastimil Babka <redacted>

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