[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Message-ID: <20250901123028.3383461-1-max.kellermann@ionos.com>
Date: Mon, 1 Sep 2025 14:30:16 +0200
From: Max Kellermann <max.kellermann@...os.com>
To: akpm@...ux-foundation.org,
david@...hat.com,
axelrasmussen@...gle.com,
yuanchu@...gle.com,
willy@...radead.org,
hughd@...gle.com,
mhocko@...e.com,
linux-kernel@...r.kernel.org,
linux-mm@...ck.org,
lorenzo.stoakes@...cle.com,
Liam.Howlett@...cle.com,
vbabka@...e.cz,
rppt@...nel.org,
surenb@...gle.com,
vishal.moola@...il.com,
linux@...linux.org.uk,
James.Bottomley@...senPartnership.com,
deller@....de,
agordeev@...ux.ibm.com,
gerald.schaefer@...ux.ibm.com,
hca@...ux.ibm.com,
gor@...ux.ibm.com,
borntraeger@...ux.ibm.com,
svens@...ux.ibm.com,
davem@...emloft.net,
andreas@...sler.com,
dave.hansen@...ux.intel.com,
luto@...nel.org,
peterz@...radead.org,
tglx@...utronix.de,
mingo@...hat.com,
bp@...en8.de,
x86@...nel.org,
hpa@...or.com,
chris@...kel.net,
jcmvbkbc@...il.com,
viro@...iv.linux.org.uk,
brauner@...nel.org,
jack@...e.cz,
weixugc@...gle.com,
baolin.wang@...ux.alibaba.com,
rientjes@...gle.com,
shakeel.butt@...ux.dev,
max.kellermann@...os.com,
thuth@...hat.com,
broonie@...nel.org,
osalvador@...e.de,
jfalempe@...hat.com,
mpe@...erman.id.au,
nysal@...ux.ibm.com,
linux-arm-kernel@...ts.infradead.org,
linux-parisc@...r.kernel.org,
linux-s390@...r.kernel.org,
sparclinux@...r.kernel.org,
linux-fsdevel@...r.kernel.org
Subject: [PATCH v5 00/12] mm: establish const-correctness for pointer parameters
For improved const-correctness.
This patch series systematically adds const qualifiers to pointer
parameters throughout the memory management subsystem, establishing a
foundation for improved const-correctness across the entire Linux
kernel.
Const-correctness provides multiple benefits:
1. Type Safety: The compiler enforces that functions marked as taking
const parameters cannot accidentally modify the data, catching
potential bugs at compile time rather than runtime.
2. Compiler Optimizations: When the compiler knows data won't be
modified, it can generate more efficient code through better
register allocation, code motion, and aliasing analysis.
3. API Documentation: Const qualifiers serve as self-documenting code,
making it immediately clear to developers which functions are
read-only operations versus those that modify state.
4. Maintenance Safety: Future modifications to const-correct code are
less likely to introduce subtle bugs, as the compiler will reject
attempts to modify data that should remain unchanged.
The memory management subsystem is a fundamental building block of the
kernel. Most higher-level kernel subsystems (filesystems, drivers,
networking) depend on mm interfaces. By establishing
const-correctness at this foundational level:
1. Enables Propagation: Higher-level subsystems can adopt
const-correctness in their own interfaces. Without const-correct
mm functions, filesystems cannot mark their own parameters const
when they need to call mm functions.
2. Maximum Impact: Changes to core mm APIs benefit the entire kernel, as
these functions are called from virtually every subsystem.
3. Prevents Impedance Mismatch: Without const-correctness in mm, other
subsystems must either cast away const (dangerous) or avoid using
const altogether (missing optimization opportunities).
Each patch focuses on a specific header or subsystem component to ease review
and bisection.
This work was initially posted as a single large patch:
https://lore.kernel.org/lkml/20250827192233.447920-1-max.kellermann@ionos.com/
Following feedback from Lorenzo Stoakes and David Hildenbrand, it has been
split into focused, reviewable chunks. The approach was validated with a
smaller patch that received agreement:
https://lore.kernel.org/lkml/20250828130311.772993-1-max.kellermann@ionos.com/
Signed-off-by: Max Kellermann <max.kellermann@...os.com>
---
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
Max Kellermann (12):
mm: constify shmem related test functions for improved
const-correctness
mm: constify pagemap related test functions for improved
const-correctness
mm: constify zone related test functions for improved
const-correctness
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 functions for improved
const-correctness
parisc: constify mmap_upper_limit() parameter for improved
const-correctness
mm: constify arch_pick_mmap_layout() for improved const-correctness
mm: constify ptdesc_pmd_pts_count() and folio_get_private()
mm: constify various inline test 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 | 7 ++--
arch/sparc/kernel/sys_sparc_64.c | 3 +-
arch/x86/mm/mmap.c | 7 ++--
arch/xtensa/include/asm/highmem.h | 2 +-
include/linux/fs.h | 7 ++--
include/linux/highmem-internal.h | 44 +++++++++++----------
include/linux/highmem.h | 8 ++--
include/linux/mm.h | 56 +++++++++++++--------------
include/linux/mm_inline.h | 26 +++++++------
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 | 7 ++--
mm/shmem.c | 6 +--
mm/util.c | 20 ++++++----
21 files changed, 171 insertions(+), 155 deletions(-)
--
2.47.2
Powered by blists - more mailing lists