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

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Message-ID: <2e80e8b2-0bfe-47d2-9388-be077af04e37@lucifer.local>
Date: Mon, 13 Jan 2025 17:18:26 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        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 Wed, Jan 08, 2025 at 11:02:57PM +0100, David Hildenbrand wrote:
> 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 :) )

Matthew pinged me on irc with mapping_wrprotect_page() :>)

Am happy to do that, will respin in a bit anyway...

>
> --
> Cheers,
>
> David / dhildenb
>