Re: [RFC PATCH v5 3/4] mm/vmscan: avoid pointless large folio splits without swap

[David Hildenbrand (Arm)]

On 7/30/26 14:23, Xueyuan Chen wrote:
> From: "Barry Song (Xiaomi)" <baohua@xxxxxxxxxx>
> 
> When swap is disabled, exhausted, or unavailable due to memcg swap
> limits, splitting a large anonymous folio cannot make swapout progress.
> The fallback only destroys the large folio and inflates split statistics.
> 
> Use -E2BIG from folio_alloc_swap() as the explicit signal that splitting
> the folio might allow swapout of smaller pieces. For other allocation
> failures, keep the existing activation path and avoid the split.
> 
> This preserves the split fallback for fragmented or partially available
> swap, while avoiding it when there is no backing space for any part of the
> folio.
> 
> Reported-by: Nanzhe Zhao <zhaonanzhe@xxxxxxxxxx>

Do you have a link to the report?

I assume this is not Fixes-worthy.

> Signed-off-by: Barry Song (Xiaomi) <baohua@xxxxxxxxxx>
> Signed-off-by: Xueyuan Chen <xueyuan.chen21@xxxxxxxxx>
> ---
>  mm/vmscan.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 26df81e773ff..457049e130df 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1263,6 +1263,8 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
>  		 */
>  		if (folio_test_anon(folio) && folio_test_swapbacked(folio) &&
>  				!folio_test_swapcache(folio)) {
> +			int ret;
> +
>  			if (!(sc->gfp_mask & __GFP_IO))
>  				goto keep_locked;
>  			if (folio_maybe_dma_pinned(folio))
> @@ -1281,11 +1283,14 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
>  				    split_folio_to_list(folio, folio_list))
>  					goto activate_locked;
>  			}
> -			if (folio_alloc_swap(folio)) {
> +			ret = folio_alloc_swap(folio);
> +			if (ret) {
>  				int __maybe_unused order = folio_order(folio);
>  
>  				if (!folio_test_large(folio))
>  					goto activate_locked_split;
> +				if (ret != -E2BIG)
> +					goto activate_locked;
>  				/* Fallback to swap normal pages */
>  				if (split_folio_to_list(folio, folio_list))
>  					goto activate_locked;

Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

-- 
Cheers,

David