Re: [RFC PATCH 0/6] Drain remote per-cpu directly

[Marcelo Tosatti]

On Tue, Apr 26, 2022 at 01:06:12PM +0200, Nicolas Saenz Julienne wrote:
> On Mon, 2022-04-25 at 15:58 -0700, Minchan Kim wrote:
> > On Wed, Apr 20, 2022 at 10:59:00AM +0100, Mel Gorman wrote:
> > > This series has the same intent as Nicolas' series "mm/page_alloc: Remote
> > > per-cpu lists drain support" -- avoid interference of a high priority
> > > task due to a workqueue item draining per-cpu page lists. While many
> > > workloads can tolerate a brief interruption, it may be cause a real-time
> > > task runnning on a NOHZ_FULL CPU to miss a deadline and at minimum,
> > > the draining in non-deterministic.
> > 
> > Yeah, the non-deterministic is a problem. I saw the kworker-based draining
> > takes 100+ms(up to 300ms observed) sometimes in alloc_contig_range if CPUs
> > are heavily loaded.
> > 
> > I am not sure Nicolas already observed. it's not only problem of
> > per_cpu_pages but it is also lru_pvecs (pagevec) draining.
> > Do we need to introduce similar(allow remote drainning with spin_lock)
> > solution for pagevec?
> 
> Yes, I'm aware of the lru problem. I'll start working on it too once we're done
> with the page allocator (and if no-one beats me to it). That said, I don't know
> if we can apply the exact same approach, the devil is in the details. :)

I think one necessary step for that (adding spinlock to protect per-CPU
lru_pvecs) would be to find a suitable testcase.

Mel, do you have anything in mind ?



> 
> -- 
> Nicolás Sáenz
> 
>