linux-kernel - Re: [PATCH 1/2] mm: vmscan: remove folio_test

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Message-ID: <e6fc05fa-a622-47fc-acf4-9a5be98032aa@redhat.com>
Date: Fri, 12 Sep 2025 10:24:18 +0200
From: David Hildenbrand <david@...hat.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>, akpm@...ux-foundation.org,
 hannes@...xchg.org
Cc: mhocko@...nel.org, zhengqi.arch@...edance.com, shakeel.butt@...ux.dev,
 lorenzo.stoakes@...cle.com, hughd@...gle.com, willy@...radead.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm: vmscan: remove folio_test_private() check in
 pageout()

On 12.09.25 05:45, Baolin Wang wrote:
> Currently, we no longer attempt to write back filesystem folios in pageout(),
> and only tmpfs/shmem folios and anonymous swapcache folios can be written back.

Can you point me at the code where that is fenced off?

I can spot a folio_is_file_lru() check before we call it, but the 
description tells me that there are indeed ways we could still pass that 
check for file-lru folios if we are kswapd.

> Moreover, tmpfs/shmem and swapcache folios do not use the PG_private flag,
> which means no fs-private private data is used. Therefore, we can remove the
> redundant folio_test_private() checks and related buffer_head release logic.

If that's indeed the case, do we still need the folio_test_private() 
check in is_page_cache_freeable()?

> 
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> ---
>   mm/vmscan.c | 16 +---------------
>   1 file changed, 1 insertion(+), 15 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index f1fc36729ddd..8056fccb9cc4 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -697,22 +697,8 @@ static pageout_t pageout(struct folio *folio, struct address_space *mapping,
>   	 * swap_backing_dev_info is bust: it doesn't reflect the
>   	 * congestion state of the swapdevs.  Easy to fix, if needed.
>   	 */
> -	if (!is_page_cache_freeable(folio))
> +	if (!is_page_cache_freeable(folio) || !mapping)
>   		return PAGE_KEEP;
> -	if (!mapping) {
> -		/*
> -		 * Some data journaling orphaned folios can have
> -		 * folio->mapping == NULL while being dirty with clean buffers.
> -		 */
> -		if (folio_test_private(folio)) {
> -			if (try_to_free_buffers(folio)) {
> -				folio_clear_dirty(folio);
> -				pr_info("%s: orphaned folio\n", __func__);
> -				return PAGE_CLEAN;
> -			}
> -		}
> -		return PAGE_KEEP;
> -	}
>   
>   	if (!shmem_mapping(mapping) && !folio_test_anon(folio))
>   		return PAGE_ACTIVATE;


-- 
Cheers

David / dhildenb