Re: [PATCH v5 08/14] mm/mglru: remove redundant swap constrained check upon isolation

[Chen Ridong]

On 2026/4/13 0:48, Kairui Song via B4 Relay wrote:
> From: Kairui Song <kasong@xxxxxxxxxxx>
> 
> Remove the swap-constrained early reject check upon isolation. This
> check is a micro optimization when swap IO is not allowed, so folios are
> rejected early. But it is redundant and overly broad since
> shrink_folio_list() already handles all these cases with proper
> granularity.
> 
> Notably, this check wrongly rejected lazyfree folios, and it doesn't
> cover all rejection cases. shrink_folio_list() uses may_enter_fs(),
> which distinguishes non-SWP_FS_OPS devices from filesystem-backed swap
> and does all the checks after folio is locked, so flags like swap cache
> are stable.
> 
> This check also covers dirty file folios, which are not a problem now
> since sort_folio() already bumps dirty file folios to the next
> generation, but causes trouble for unifying dirty folio writeback
> handling.
> 
> And there should be no performance impact from removing it. We may have
> lost a micro optimization, but unblocked lazyfree reclaim for NOIO
> contexts, which is not a common case in the first place.
> 
> Reviewed-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
> Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
> ---
>  mm/vmscan.c | 6 ------
>  1 file changed, 6 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 5ae6bd967b17..965d8905a4fe 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4650,12 +4650,6 @@ static bool isolate_folio(struct lruvec *lruvec, struct folio *folio, struct sca
>  {
>  	bool success;
>  
> -	/* swap constrained */
> -	if (!(sc->gfp_mask & __GFP_IO) &&
> -	    (folio_test_dirty(folio) ||
> -	     (folio_test_anon(folio) && !folio_test_swapcache(folio))))
> -		return false;
> -
>  	/* raced with release_pages() */
>  	if (!folio_try_get(folio))
>  		return false;
> 

Reviewed-by: Chen Ridong <chenridong@xxxxxxxxxxxxxxx>

-- 
Best regards,
Ridong