Re: [PATCH -next] mm: introduce per-node proactive reclaim interface

[Michal Hocko]

On Fri 06-09-24 19:04:19, Hillf Danton wrote:
> On Thu, 5 Sep 2024 16:29:41 -0700 Davidlohr Bueso <dave@xxxxxxxxxxxx>
> > On Fri, 06 Sep 2024, Hillf Danton wrote:\n
> > >The proactive reclaim on the cmdline looks like waste of cpu cycles before
> > >the cases where kswapd fails to work are spotted. It is not correct to add
> > >it because you can type the code.
> > 
> > Are you against proactive reclaim altogether (ie: memcg) or this patch in
> > particular, which extends its availability?
> > 
> The against makes no sense to me because I know your patch is never able to
> escape standing ovation.

I fail to understand your reasoning. Do you have any actual technical
arguments why this is a bad idea?

> > The benefits of proactive reclaim are well documented, and the community has
> > been overall favorable towards it. This operation is not meant to be generally
> > used, but there are real latency benefits to be had which are completely
> > unrelated to watermarks. Similarly, we have 'compact' as an alternative to
> > kcompactd (which was once upon a time part of kswapd).
> >
> Because kswapd is responsible for watermark instead of high order pages,
> compact does not justify proactive reclaim from the begining.

What do you mean? How does keeping a global watermark helps to trigger
per NUMA node specific aging - e.g. demotion? Or do you dispute the
overall idea and have a different idea how to achieve those usecases?
-- 
Michal Hocko
SUSE Labs