Re: [linux-next:master] [mm] 1111d46b5c: stress-ng.pthread.ops_per_sec -84.3% regression

Yin Fengwei
2023-12-21T04:58:38Z

On 2023/12/21 12:49, Matthew Wilcox wrote:
> On Thu, Dec 21, 2023 at 08:58:42AM +0800, Yin Fengwei wrote:
>> Yes. MAP_STACK is also mentioned in manpage of mmap. I did test to
>> filter out of the MAP_STACK mapping based on this patch. The regression
>> in stress-ng.pthread was gone. I suppose this is kind of safe because
>> the madvise call is only applied to glibc allocated stack.
>>
>>
>> But what I am not sure was whether it's worthy to do such kind of change
>> as the regression only is seen obviously in micro-benchmark. No evidence
>> showed the other regressionsin this report is related with madvise. At
>> least from the perf statstics. Need to check more on stream/ramspeed.
>
> FWIW, we had a customer report a significant performance problem when
> inadvertently using 2MB pages for stacks. They were able to avoid it by
> using 2044KiB sized stacks ...
Looks like related with this regression. So we may need to consider
avoiding THP for stack.

Regards
Yin, Fengwei