Re: [PATCH v2] mm/vmstat: fold stranded per-cpu node stats when a node comes online

[Gregory Price <gourry@gourry.net>]

On Tue, Jun 30, 2026 at 03:55:17PM -0700, Andrew Morton wrote:
> On Tue, 30 Jun 2026 16:57:43 -0400 Gregory Price <gourry@gourry.net> wrote:
> 
> > On Sat, Jun 27, 2026 at 04:10:07PM -0700, Andrew Morton wrote:
> > > On Sat, 27 Jun 2026 16:22:43 -0400 Gregory Price <gourry@gourry.net> wrote:
> > > 
> > > > +		struct per_cpu_nodestat *p = per_cpu_ptr(pgdat->per_cpu_nodestats, cpu);
> > > >  
> > > > -		p = per_cpu_ptr(pgdat->per_cpu_nodestats, cpu);
> > > > +		for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++)
> > > 
> > > and that's a lot of items.
> > > 
> > > I guess the overall loop count won't be large enough to cause issues,
> > > but it's large!
> > > 
> > > Perhaps there's some simple test we can do on the per_cpu_nodestat to
> > > avoid the inner loop?  Perhaps might need to add a field for this?
> > >
> > 
> > I took a look, but that would involve adding another per-cpu field and
> > then making sure all the races on that field are respected as well.
> > 
> > Not sure it's worth it for such an extremely rare event.
> > 
> > I can try to get clever on the folding logic if you'd like, let me know.
> > 
> > > btw, "for(int i..." is allowed nowadays.  It'll make this code nicer, IMO.
> > > 
> > 
> > Otherwise i can send you a respin for this.
> 
> Is OK, we could make this change in a million other places.
> 
> > > And... Sashiko seems to have found a pre-existing issue:
> > > 	https://sashiko.dev/#/patchset/20260627202243.758289-1-gourry@gourry.net
> > > 
> > 
> > Incoming patch for this shortly.  Pretty trivial.
> 
> Cool, what was the Subject?
>

[PATCH] mm/mm_init: handle alloc_percpu failure in free_area_init_core_hotplug

https://lore.kernel.org/linux-mm/20260630214039.2263562-1-gourry@gourry.net/T/#u

I didn't bother with Cc:stable because it's also 10 years old and
doesn't seem likely to actually get hit, but if you think it should be
stable let me know.

> 
> I'll queue this patch in mm-hotfixes for some testing while we await
> further review (please).
>

Thank you!

~Gregory