Re: [PATCH 0/6 v2] Calculate pcp->high based on zone sizes and active CPUs

[David Hildenbrand]

On 28.05.21 10:55, Mel Gorman wrote:
> On Thu, May 27, 2021 at 12:36:21PM -0700, Dave Hansen wrote:
> > Hi Mel,
> >
> > Feng Tang tossed these on a "Cascade Lake" system with 96 threads and
> > ~512G of persistent memory and 128G of DRAM.  The PMEM is in "volatile
> > use" mode and being managed via the buddy just like the normal RAM.
> >
> > The PMEM zones are big ones:
> >
> >          present  65011712 = 248 G
> >          high       134595 = 525 M
> >
> > The PMEM nodes, of course, don't have any CPUs in them.
> >
> > With your series, the pcp->high value per-cpu is 69584 pages or about
> > 270MB per CPU.  Scaled up by the 96 CPU threads, that's ~26GB of
> > worst-case memory in the pcps per zone, or roughly 10% of the size of
> > the zone.

When I read about having such big amounts of free memory theoretically 
stuck in PCP lists, I guess we really want to start draining the PCP in 
alloc_contig_range(), just as we do with memory hotunplug when offlining.

--
Thanks,

David / dhildenb