Re: [PATCH v5 14/36] mm/damon: skip private node memory in DAMON migration and pageout

On Tue, Jul 21, 2026 at 04:46:43PM -0700, SJ Park wrote:
> On Mon, 20 Jul 2026 15:34:08 -0400 Gregory Price <[email protected]> wrote:
> 
> > DAMON operates on physical address ranges, which can cover private
> > node memory. Skip private-node folios in both DAMON's migration
> > and reclaim paths.
> > 
> > Signed-off-by: Gregory Price <[email protected]>
> > ---
> >  mm/damon/paddr.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
> > index e4f98d67461f5..c741a94319750 100644
> > --- a/mm/damon/paddr.c
> > +++ b/mm/damon/paddr.c
> > @@ -12,6 +12,7 @@
> >  #include <linux/swap.h>
> >  #include <linux/memory-tiers.h>
> >  #include <linux/mm_inline.h>
> > +#include <linux/node_private.h>
> >  
> >  #include "../internal.h"
> >  #include "ops-common.h"
> > @@ -250,6 +251,10 @@ static unsigned long damon_pa_pageout(struct damon_region *r,
> >  			continue;
> >  		}
> >  
> > +		/* private node memory is not reclaimable by default */
> > +		if (folio_is_private_node(folio))
> > +			goto put_folio;
> > +
> 
> "by default".  Does that mean it could be reclaimable in some situations?  If
> so, could we check if it is reclaimable?
> 

See the damon changes in:

https://lore.kernel.org/linux-mm/al-pkvmgIxGu3LzM@gourry-fedora-PF4VCD3F/T/#mfb99303c85dd9d4c3f58832dc28fc55583a7217a

> Also, what happens if we just try paging out the private node memory?  Will it
> simply fail?  Or, make some problems?
> 

user controls for MADV_ commands that affect private node folios would
skip those folios - exactly same as ZONE_DEVICE folios.

Which I'm not sure damon actually handles correctly presently (zone
device).  I remember looking around damon and thinking to myself "what
if this is a zone device page?" and not being able to find a satisfying
answer.

> >  		if (damos_pa_filter_out(s, folio))
> >  			goto put_folio;
> >  		else
> > @@ -344,6 +349,10 @@ static unsigned long damon_pa_migrate(struct damon_region *r,
> >  		else
> >  			*sz_filter_passed += folio_size(folio) / addr_unit;
> >  
> > +		/* private nodes do not support migration by default */
> > +		if (folio_is_private_node(folio))
> > +			goto put_folio;
> > +
> 
> Same questions.
> 

Technically there is nothing in migration core to prevent migration
operations, it's done on a service basis - hotunplug, reclaim/demotion,
user numa (mbind, migrate/move_pages) etc.

Operations on private nodes/private node folioes are refused if the
capability bit is not set.

~Gregory