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

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

[dayou5941]

From: liyouhong <liyouhong@kylinos.cn>

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: <stable@vger.kernel.org>
Assisted-by: Cursor:grok-4.5
Signed-off-by: liyouhong <liyouhong@kylinos.cn>

---
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;
+	}
 
 	noreclaim_flag = memalloc_noreclaim_save();
 
-- 
2.25.1

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

[SJ Park]

'checkpatch.pl --nogit --nogit-fallback' suggests adding below recipients.  I
added them.  Please consider using get_maintainer.pl from next time.

- Joshua Hahn <joshua.hahnjy@gmail.com>
- linux-mm@kvack.org
- linux-kernel@vger.kernel.org


On Fri, 24 Jul 2026 14:01:34 +0800 dayou5941@163.com wrote:

> From: liyouhong <liyouhong@kylinos.cn>
> 
> 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.

Thank you for finding and fixing this!

> 
> Fixes: 7e6c3130690a ("mm/damon/ops-common: ignore migration request to invalid nodes")
> Cc: <stable@vger.kernel.org>
> Assisted-by: Cursor:grok-4.5
> Signed-off-by: liyouhong <liyouhong@kylinos.cn>

Reviewed-by: SJ Park <sj@kernel.org>


Thanks,
SJ

[...]

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

[SJ Park]

On Fri, 24 Jul 2026 07:26:38 -0700 SJ Park <sj@kernel.org> wrote:

> 
> 'checkpatch.pl --nogit --nogit-fallback' suggests adding below recipients.  I

I mean, get_maintainer.pl.  Sorry if it confused you.


THanks,
SJ

[...]

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

[SJ Park]

On Fri, 24 Jul 2026 14:01:34 +0800 dayou5941@163.com wrote:

> From: liyouhong <liyouhong@kylinos.cn>
> 
> 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: <stable@vger.kernel.org>
> Assisted-by: Cursor:grok-4.5
> Signed-off-by: liyouhong <liyouhong@kylinos.cn>
> 
> ---
> 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.


Thanks,
SJ

[...]

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

[SJ Park]

On Fri, 24 Jul 2026 07:41:46 -0700 SJ Park <sj@kernel.org> wrote:

> On Fri, 24 Jul 2026 14:01:34 +0800 dayou5941@163.com wrote:
> 
> > From: liyouhong <liyouhong@kylinos.cn>
> > 
> > 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: <stable@vger.kernel.org>
> > Assisted-by: Cursor:grok-4.5
> > Signed-off-by: liyouhong <liyouhong@kylinos.cn>
> > 
> > ---
> > 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

[...]