On 2024/8/17 2:15, Matthew Wilcox wrote:

> On Fri, Aug 16, 2024 at 05:13:27PM +0800, Nanyong Sun wrote:
>> Now the large folio control interfaces is system wide and tend to be
>> default on: file systems use large folio by default if supported,
>> mTHP is tend to default enable when boot [1].
>> When large folio enabled, some workloads have performance benefit,
>> but some may not and some side effects can happen: the memory usage
>> may increase, direct reclaim maybe more frequently because of more
>> large order allocations, result in cpu usage also increases. We observed
>> this on a product environment which run nginx, the pgscan_direct count
>> increased a lot than before, can reach to 3000 times per second, and
>> disable file large folio can fix this.
> Can you share any details of your nginx workload that shows a regression?
> The heuristics for allocating large folios are completely untuned, so
> having data for a workload which performs better with small folios is
> very valuable.
>
> .
The RPS(/Requests per second/) which is the performance metric of nginx 
workload has no
regression(also no improvement)，we just observed that  pgscan_direct 
rate is much higher
with large folio.
So far, we have tested some workloads' benchmark, some did not have 
performance improvement
but also did not have regression.
In a production environment, different workloads may be deployed on a 
machine. Therefore,
do we need to add a process/cgroup level control to prevent workloads 
that will not have
performance improvement from using mTHP? In this way, the memory 
overhead and direct reclaim
caused by mTHP can be avoided for those process/cgroup.