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

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Message-ID: <9ef12649-7e82-4b5a-8090-e0645ffbf3dc@redhat.com>
Date: Wed, 8 Jan 2025 23:02:57 +0100
From: David Hildenbrand <david@...hat.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 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 22:55, Matthew Wilcox wrote:
> On Wed, Jan 08, 2025 at 10:12:36PM +0100, David Hildenbrand wrote:
>> On 08.01.25 21:54, Matthew Wilcox wrote:
>>> Not necessarily!  We already do that (since 2022) for DAX (see
>>> 6a8e0596f004).  rmap lets you find every place that a given range
>>> of a file is mapped into user address spaces; but that file might be a
>>> device file, and so it's not just pagecache but also (in this case)
>>> fb memory, and whatever else device drivers decide to mmap.
>>
>> Yes, that part I remember.
>>
>> I thought we would be passing in a page into rmap_wrprotect_file_page(), and
>> was wondering what we would do to "struct page" that won't be a folio in
>> there.
>>
>> Probably, because the "_page" in rmap_wrprotect_file_page() is misleading :)
>>
>> ... should it be "file_range" ? (but we also pass the pfn ... )
> 
> I don't think it's unprecedented for us to identify a page by its pfn.
> After all, the acronym stands for "page frame number".  That said, for
> the one caller of this, it has the struct page and passes in the result
> from page_to_pfn().  So no harm in passing in the struct page directly.
> 
> I would not like to see this function called "rmap_wrprotect_file_pfn".
> Files don't have pfns, so that's a bad name.

Agreed.

(it's too late in the evening for me to give any good suggestions :) )

-- 
Cheers,

David / dhildenb