Re: [PATCH v6 00/12] mm: establish const-correctness for pointer parameters

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Mon, Sep 01, 2025 at 10:50:09PM +0200, Max Kellermann wrote:
> For improved const-correctness in the low-level memory-management
> subsystem, which provides a basis for further const-ification further
> up the call stack (e.g. filesystems).

Great, this succinctly expresses what you want!

>
> This patch series splitted into smaller patches was initially posted
> as a single large patch:
>
>  https://lore.kernel.org/lkml/20250827192233.447920-1-max.kellermann@ionos.com/
>
> I started this work when I tried to constify the Ceph filesystem code,
> but found that to be impossible because many "mm" functions accept
> non-const pointer, even though they modify nothing.

And as Vlasta said, this is great context.

>
> Signed-off-by: Max Kellermann <max.kellermann@ionos.com>

Glad we got there in the end :) hopefully having more const-ification will have
a knock-on effect anyway for future development both by:

a. People needing to ensure it downstream of this stuff &.
b. Seeing the pattern and adopting it.

So this should have a positive impact I think :)

Cheers, Lorenzo

> ---
> v1 -> v2:
> - made several parameter values const (i.e. the pointer address, not
>   just the pointed-to memory), as suggested by Andrew Morton and
>   Yuanchu Xie
> - drop existing+obsolete "extern" keywords on lines modified by these
>   patches (suggested by Vishal Moola)
> - add missing parameter names on lines modified by these patches
>   (suggested by Vishal Moola)
> - more "const" pointers (e.g. the task_struct passed to
>   process_shares_mm())
> - add missing "const" to s390, fixing s390 build failure
> - moved the mmap_is_legacy() change in arch/s390/mm/mmap.c from 08/12
>   to 06/12 (suggested by Vishal Moola)
>
> v2 -> v3:
> - remove garbage from 06/12
> - changed tags on subject line (suggested by Matthew Wilcox)
>
> v3 -> v4:
> - more verbose commit messages including a listing of function names
>   (suggested by David Hildenbrand and Lorenzo Stoakes)
>
> v4 -> v5:
> - back to shorter commit messages after an agreement between David
>   Hildenbrand and Lorenzo Stoakes was found
>
> v5 -> v6:
> - fix inconsistent constness of assert_fault_locked()
> - revert the const parameter value change from v2 (requested by
>   Lorenzo Stoakes)
> - revert the long cover letter, removing long explanations again
>   (requested by Lorenzo Stoakes)
>
> Max Kellermann (12):
>   mm: constify shmem related test functions for improved
>     const-correctness
>   mm: constify pagemap related test/getter functions
>   mm: constify zone related test/getter functions
>   fs: constify mapping related test functions for improved
>     const-correctness
>   mm: constify process_shares_mm() for improved const-correctness
>   mm, s390: constify mapping related test/getter functions
>   parisc: constify mmap_upper_limit() parameter
>   mm: constify arch_pick_mmap_layout() for improved const-correctness
>   mm: constify ptdesc_pmd_pts_count() and folio_get_private()
>   mm: constify various inline functions for improved const-correctness
>   mm: constify assert/test functions in mm.h
>   mm: constify highmem related functions for improved const-correctness
>
>  arch/arm/include/asm/highmem.h      |  6 +--
>  arch/parisc/include/asm/processor.h |  2 +-
>  arch/parisc/kernel/sys_parisc.c     |  2 +-
>  arch/s390/mm/mmap.c                 |  6 +--
>  arch/sparc/kernel/sys_sparc_64.c    |  2 +-
>  arch/x86/mm/mmap.c                  |  6 +--
>  arch/xtensa/include/asm/highmem.h   |  2 +-
>  include/linux/fs.h                  |  6 +--
>  include/linux/highmem-internal.h    | 36 +++++++++---------
>  include/linux/highmem.h             |  8 ++--
>  include/linux/mm.h                  | 56 +++++++++++++--------------
>  include/linux/mm_inline.h           | 25 ++++++------
>  include/linux/mm_types.h            |  4 +-
>  include/linux/mmzone.h              | 42 ++++++++++----------
>  include/linux/pagemap.h             | 59 +++++++++++++++--------------
>  include/linux/sched/mm.h            |  4 +-
>  include/linux/shmem_fs.h            |  4 +-
>  mm/highmem.c                        | 10 ++---
>  mm/oom_kill.c                       |  6 +--
>  mm/shmem.c                          |  6 +--
>  mm/util.c                           | 16 ++++----
>  21 files changed, 155 insertions(+), 153 deletions(-)
>
> --
> 2.47.2
>