On Tue, 15 Aug 2017 16:45:34 +0800
Kemi Wang <kemi.wang@xxxxxxxxx> wrote:
> Each page allocation updates a set of per-zone statistics with a call to
> zone_statistics(). As discussed in 2017 MM submit, these are a substantial
^^^^^^ should be "summit"
> source of overhead in the page allocator and are very rarely consumed. This
> significant overhead in cache bouncing caused by zone counters (NUMA
> associated counters) update in parallel in multi-threaded page allocation
> (pointed out by Dave Hansen).
Hi Kemi
Thanks a lot for following up on this work. A link to the MM summit slides:
http://people.netfilter.org/hawk/presentations/MM-summit2017/MM-summit2017-JesperBrouer.pdf
> To mitigate this overhead, this patchset separates NUMA statistics from
> zone statistics framework, and update NUMA counter threshold to a fixed
> size of 32765, as a small threshold greatly increases the update frequency
> of the global counter from local per cpu counter (suggested by Ying Huang).
> The rationality is that these statistics counters don't need to be read
> often, unlike other VM counters, so it's not a problem to use a large
> threshold and make readers more expensive.
>
> With this patchset, we see 26.6% drop of CPU cycles(537-->394, see below)
> for per single page allocation and reclaim on Jesper's page_bench03
> benchmark. Meanwhile, this patchset keeps the same style of virtual memory
> statistics with little end-user-visible effects (see the first patch for
> details), except that the number of NUMA items in each cpu
> (vm_numa_stat_diff[]) is added to zone->vm_numa_stat[] when a user *reads*
> the value of NUMA counter to eliminate deviation.
I'm very happy to see that you found my kernel module for benchmarking useful :-)
> I did an experiment of single page allocation and reclaim concurrently
> using Jesper's page_bench03 benchmark on a 2-Socket Broadwell-based server
> (88 processors with 126G memory) with different size of threshold of pcp
> counter.
>
> Benchmark provided by Jesper D Broucer(increase loop times to 10000000):
^^^^^^^
You mis-spelled my last name, it is "Brouer".
> https://github.com/netoptimizer/prototype-kernel/tree/master/kernel/mm/bench
>
> Threshold CPU cycles Throughput(88 threads)
> 32 799 241760478
> 64 640 301628829
> 125 537 358906028 <==> system by default
> 256 468 412397590
> 512 428 450550704
> 4096 399 482520943
> 20000 394 489009617
> 30000 395 488017817
> 32765 394(-26.6%) 488932078(+36.2%) <==> with this patchset
> N/A 342(-36.3%) 562900157(+56.8%) <==> disable zone_statistics
>
> Kemi Wang (2):
> mm: Change the call sites of numa statistics items
> mm: Update NUMA counter threshold size
>
> drivers/base/node.c | 22 ++++---
> include/linux/mmzone.h | 25 +++++---
> include/linux/vmstat.h | 33 ++++++++++
> mm/page_alloc.c | 10 +--
> mm/vmstat.c | 162 +++++++++++++++++++++++++++++++++++++++++++++++--
> 5 files changed, 227 insertions(+), 25 deletions(-)
>
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
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