linux-kernel - Re: [PATCH] mm: remove io-mapping

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Message-ID: <f9cf2e9c-6ff3-4a0f-a6d8-226f37f2bfa0@lucifer.local>
Date: Fri, 25 Jul 2025 15:23:38 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Jonathan Corbet <corbet@....net>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: remove io-mapping

On Thu, Jul 24, 2025 at 12:53:00PM -0600, Jonathan Corbet wrote:
> Lorenzo Stoakes <lorenzo.stoakes@...cle.com> writes:
>
> > This is dead code, which was used from commit b739f125e4eb ("i915: use
> > io_mapping_map_user") but reverted a month later by commit
> > 0e4fe0c9f2f9 ("Revert "i915: use io_mapping_map_user"") back in 2021.
> >
> > Since then nobody has used it, so remove it.
> >
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> > ---
> >  include/linux/io-mapping.h | 231 -------------------------------------
> >  mm/Kconfig                 |   4 -
> >  mm/Makefile                |   1 -
> >  mm/io-mapping.c            |  30 -----
> >  4 files changed, 266 deletions(-)
> >  delete mode 100644 include/linux/io-mapping.h
> >  delete mode 100644 mm/io-mapping.c
>
> [...]
>
> > -/*
> > - * The io_mapping mechanism provides an abstraction for mapping
> > - * individual pages from an io device to the CPU in an efficient fashion.
> > - *
> > - * See Documentation/driver-api/io-mapping.rst
> > - */
> 				      ^
> 				      |
> You'll want to get rid of that file --+ too
>
> jon

Thanks for this, but it turns out we aren't getting rid of the header at
all (doh!) just io_mapping_map_user()... It's been a long week :)

Cheers, Lorenzo