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

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Message-ID: <11629632-c652-460e-b617-3ec0c27969f5@linux.alibaba.com>
Date: Sat, 13 Sep 2025 11:04:48 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: akpm@...ux-foundation.org, hannes@...xchg.org, david@...hat.com,
 mhocko@...nel.org, zhengqi.arch@...edance.com, shakeel.butt@...ux.dev,
 lorenzo.stoakes@...cle.com, hughd@...gle.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm: vmscan: remove folio_test_private() check in
 pageout()



On 2025/9/12 23:21, Matthew Wilcox wrote:
> On Fri, Sep 12, 2025 at 11:45:07AM +0800, Baolin Wang wrote:
>> @@ -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;
> 
> I feel like we need to keep the comment (assuming it's still true ...
> which it probably is, although there's nobody who would think to update
> this comment if it became no longer true).  I would certainly wonder why
> we can have this !mapping test.

I think the !mapping check is still needed here because the tmpfs/shmem 
folios truncation might race with folio reclamation, see shmem_undo_range().

Additionally, the comments here are no longer related to tmpfs/shmem and 
swapcache folios, so I still prefer to remove them.

>> -		/*
>> -		 * Some data journaling orphaned folios can have
>> -		 * folio->mapping == NULL while being dirty with clean buffers.
>> -		 */
> 
> I approve of this simplification, and I think there's more work to be
> done in this area.  Thanks for doing it.

Thanks for taking a look. Yes, I will continue to take a closer look at 
the further work here.