Re: [PATCH v13 3/6] mm/vmstat: manage per-CPU stats from CPU context when NOHZ full

[Marcelo Tosatti]

On Tue, Jan 10, 2023 at 10:43:56AM +0800, Hillf Danton wrote:
> On 9 Jan 2023 11:12:49 -0300 Marcelo Tosatti <mtosatti@xxxxxxxxxx>
> > 
> > Yes, but if you do not return to userspace, then the per-CPU vm
> > statistics can be dirty indefinitely.
> 
> Could you specify the reasons for failing to return to userspace,
> given it is undesired intereference for the shepherd to queue work
> on the isolated CPUs.

Any system call that takes longer than the threshold to sync vmstats.

Or a long running kernel thread, for example:

https://stackoverflow.com/questions/65111483/long-running-kthread-and-synchronize-net