Re: [PATCH v2 1/2] mm/damon/ops-common: putback folios on invalid migrate nid

On Fri, 24 Jul 2026 07:41:46 -0700 SJ Park <[email protected]> wrote:

> On Fri, 24 Jul 2026 14:01:34 +0800 [email protected] wrote:
> 
> > From: liyouhong <[email protected]>
> > 
> > damon_pa_migrate() and damos_va_migrate() isolate folios into a local list
> > and then call damon_migrate_pages().  When target_nid is invalid (including
> > the scheme default NUMA_NO_NODE / -1), damon_migrate_pages() returns early
> > without putting the folios back to the LRU.
> > 
> > Callers then discard the list head while those folios remain isolated with
> > an extra reference taken by folio_isolate_lru().  The pages stay off the
> > LRU for as long as the mapping exists (anon active+inactive counts drop
> > while RSS does not), and the leftover references can pin the pages after
> > the mapping is gone.
> > 
> > Put the folios back on the invalid-nid path so ignored migration requests
> > still return them to the LRU.
> > 
> > Fixes: 7e6c3130690a ("mm/damon/ops-common: ignore migration request to invalid nodes")
> > Cc: <[email protected]>
> > Assisted-by: Cursor:grok-4.5
> > Signed-off-by: liyouhong <[email protected]>
> > 
> > ---
> > v2:
> > - Drop the putback helper for easier stable backport
> > - Open-code putback only on the invalid-nid path
> > - Keep the original indentation and Cc stable@
> > - Add a separate cleanup as 2/2 (factor out damon_putback_folio_list)
> > 
> > ---
> >  mm/damon/ops-common.c | 9 ++++++++-
> >  1 file changed, 8 insertions(+), 1 deletion(-)
> > 
> > diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
> > index d1842e2b00ef..f5ded45fabd1 100644
> > --- a/mm/damon/ops-common.c
> > +++ b/mm/damon/ops-common.c
> > @@ -394,8 +394,15 @@ unsigned long damon_migrate_pages(struct list_head *folio_list, int target_nid)
> >  		return nr_migrated;
> >  
> >  	if (target_nid < 0 || target_nid >= MAX_NUMNODES ||
> > -			!node_state(target_nid, N_MEMORY))
> > +			!node_state(target_nid, N_MEMORY)) {
> > +		while (!list_empty(folio_list)) {
> > +			struct folio *folio = lru_to_folio(folio_list);
> > +
> > +			list_del(&folio->lru);
> > +			folio_putback_lru(folio);
> > +		}
> >  		return nr_migrated;
> > +	}
> 
> As I replied to the second patch, I'd suggest doing putback just before
> returning.  Then this invalid target_nid handling can 'goto' there.

I now think that is a bad idea.  Sorry for confusing.  That will make readers
assume damon_migrate_folio_list() doesn't putback folios.  Please resend this
as-is, but without the second patch.


Thanks,
SJ

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