linux-kernel - Re: [RFC PATCH 3/3] fb_defio: do not use deprecated page->mapping, index fields

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Message-ID: <b7465ad8-50ec-490b-a62a-e535e0a4691c@redhat.com>
Date: Wed, 8 Jan 2025 21:14:53 +0100
From: David Hildenbrand <david@...hat.com>
To: Matthew Wilcox <willy@...radead.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Jaya Kumar <jayalk@...works.biz>, Simona Vetter <simona@...ll.ch>,
 Helge Deller <deller@....de>, linux-fbdev@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org
Subject: Re: [RFC PATCH 3/3] fb_defio: do not use deprecated page->mapping,
 index fields

On 08.01.25 18:32, Matthew Wilcox wrote:
> On Wed, Jan 08, 2025 at 04:18:42PM +0000, Lorenzo Stoakes wrote:
>> @@ -280,7 +269,10 @@ static void fb_deferred_io_work(struct work_struct *work)
>>   		struct folio *folio = page_folio(pageref->page);
>>   
>>   		folio_lock(folio);
>> -		folio_mkclean(folio);
>> +		rmap_wrprotect_file_page(fbdefio->mapping,
>> +					 pageref->offset >> PAGE_SHIFT,
>> +					 compound_nr(pageref->page),
>> +					 page_to_pfn(pageref->page));
>>   		folio_unlock(folio);
> 
> Why do we need to lock the folio?  (since this isn't necessarily a
> folio) 

Can you clarify the "since this isn't necessarily a folio" part ? Do you 
mean in the future, when we split "struct page" and "struct folio"?

Doing an rmap walk on something that won't be a folio is ... sounds odd 
(->wrong :) )

-- 
Cheers,

David / dhildenb