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

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.


Thanks,
SJ

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