[PATCH] mm: constify oom_control, scan_control, and alloc_context nodemask

[PATCH] mm: constify oom_control, scan_control, and alloc_context nodemask

[Gregory Price]

The nodemasks in these structures may come from a variety of sources,
including tasks and cpusets - and should never be modified by any code
when being passed around inside another context.

Signed-off-by: Gregory Price <gourry@gourry.net>
---
 include/linux/cpuset.h | 4 ++--
 include/linux/mm.h     | 4 ++--
 include/linux/mmzone.h | 6 +++---
 include/linux/oom.h    | 2 +-
 include/linux/swap.h   | 2 +-
 kernel/cgroup/cpuset.c | 2 +-
 mm/internal.h          | 2 +-
 mm/mmzone.c            | 5 +++--
 mm/page_alloc.c        | 6 +++---
 mm/show_mem.c          | 9 ++++++---
 mm/vmscan.c            | 6 +++---
 11 files changed, 26 insertions(+), 22 deletions(-)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 65d76a38974b..a80d38e752d2 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -83,7 +83,7 @@ extern bool cpuset_cpus_allowed_fallback(struct task_struct *p);
 extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
 #define cpuset_current_mems_allowed (current->mems_allowed)
 void cpuset_init_current_mems_allowed(void);
-int cpuset_nodemask_valid_mems_allowed(nodemask_t *nodemask);
+int cpuset_nodemask_valid_mems_allowed(const nodemask_t *nodemask);
 
 extern bool cpuset_current_node_allowed(int node, gfp_t gfp_mask);
 
@@ -224,7 +224,7 @@ static inline nodemask_t cpuset_mems_allowed(struct task_struct *p)
 #define cpuset_current_mems_allowed (node_states[N_MEMORY])
 static inline void cpuset_init_current_mems_allowed(void) {}
 
-static inline int cpuset_nodemask_valid_mems_allowed(nodemask_t *nodemask)
+static inline int cpuset_nodemask_valid_mems_allowed(const nodemask_t *nodemask)
 {
 	return 1;
 }
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 485df9c2dbdd..2101e5205fc0 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4042,7 +4042,7 @@ extern int __meminit early_pfn_to_nid(unsigned long pfn);
 extern void mem_init(void);
 extern void __init mmap_init(void);
 
-extern void __show_mem(unsigned int flags, nodemask_t *nodemask, int max_zone_idx);
+extern void __show_mem(unsigned int flags, const nodemask_t *nodemask, int max_zone_idx);
 static inline void show_mem(void)
 {
 	__show_mem(0, NULL, MAX_NR_ZONES - 1);
@@ -4052,7 +4052,7 @@ extern void si_meminfo(struct sysinfo * val);
 extern void si_meminfo_node(struct sysinfo *val, int nid);
 
 extern __printf(3, 4)
-void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...);
+void warn_alloc(gfp_t gfp_mask, const nodemask_t *nodemask, const char *fmt, ...);
 
 extern void setup_per_cpu_pageset(void);
 
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index ca2712187147..919be0d9b4fa 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1815,7 +1815,7 @@ static inline int zonelist_node_idx(const struct zoneref *zoneref)
 
 struct zoneref *__next_zones_zonelist(struct zoneref *z,
 					enum zone_type highest_zoneidx,
-					nodemask_t *nodes);
+					const nodemask_t *nodes);
 
 /**
  * next_zones_zonelist - Returns the next zone at or below highest_zoneidx within the allowed nodemask using a cursor within a zonelist as a starting point
@@ -1834,7 +1834,7 @@ struct zoneref *__next_zones_zonelist(struct zoneref *z,
  */
 static __always_inline struct zoneref *next_zones_zonelist(struct zoneref *z,
 					enum zone_type highest_zoneidx,
-					nodemask_t *nodes)
+					const nodemask_t *nodes)
 {
 	if (likely(!nodes && zonelist_zone_idx(z) <= highest_zoneidx))
 		return z;
@@ -1860,7 +1860,7 @@ static __always_inline struct zoneref *next_zones_zonelist(struct zoneref *z,
  */
 static inline struct zoneref *first_zones_zonelist(struct zonelist *zonelist,
 					enum zone_type highest_zoneidx,
-					nodemask_t *nodes)
+					const nodemask_t *nodes)
 {
 	return next_zones_zonelist(zonelist->_zonerefs,
 							highest_zoneidx, nodes);
diff --git a/include/linux/oom.h b/include/linux/oom.h
index 7b02bc1d0a7e..00da05d227e6 100644
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -30,7 +30,7 @@ struct oom_control {
 	struct zonelist *zonelist;
 
 	/* Used to determine mempolicy */
-	nodemask_t *nodemask;
+	const nodemask_t *nodemask;
 
 	/* Memory cgroup in which oom is invoked, or NULL for global oom */
 	struct mem_cgroup *memcg;
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 8f0f68e245ba..bf76356d94fe 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -351,7 +351,7 @@ extern void swap_setup(void);
 /* linux/mm/vmscan.c */
 extern unsigned long zone_reclaimable_pages(struct zone *zone);
 extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
-					gfp_t gfp_mask, nodemask_t *mask);
+					gfp_t gfp_mask, const nodemask_t *mask);
 unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru, int zone_idx);
 
 #define MEMCG_RECLAIM_MAY_SWAP (1 << 1)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 5c33ab20cc20..536ce591c7ba 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -4153,7 +4153,7 @@ nodemask_t cpuset_mems_allowed(struct task_struct *tsk)
  *
  * Are any of the nodes in the nodemask allowed in current->mems_allowed?
  */
-int cpuset_nodemask_valid_mems_allowed(nodemask_t *nodemask)
+int cpuset_nodemask_valid_mems_allowed(const nodemask_t *nodemask)
 {
 	return nodes_intersects(*nodemask, current->mems_allowed);
 }
diff --git a/mm/internal.h b/mm/internal.h
index 181e79f1d6a2..a2ef9512b5bc 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -668,7 +668,7 @@ void page_alloc_sysctl_init(void);
  */
 struct alloc_context {
 	struct zonelist *zonelist;
-	nodemask_t *nodemask;
+	const nodemask_t *nodemask;
 	struct zoneref *preferred_zoneref;
 	int migratetype;
 
diff --git a/mm/mmzone.c b/mm/mmzone.c
index 0c8f181d9d50..59dc3f2076a6 100644
--- a/mm/mmzone.c
+++ b/mm/mmzone.c
@@ -43,7 +43,8 @@ struct zone *next_zone(struct zone *zone)
 	return zone;
 }
 
-static inline int zref_in_nodemask(struct zoneref *zref, nodemask_t *nodes)
+static inline int zref_in_nodemask(struct zoneref *zref,
+				   const nodemask_t *nodes)
 {
 #ifdef CONFIG_NUMA
 	return node_isset(zonelist_node_idx(zref), *nodes);
@@ -55,7 +56,7 @@ static inline int zref_in_nodemask(struct zoneref *zref, nodemask_t *nodes)
 /* Returns the next zone at or below highest_zoneidx in a zonelist */
 struct zoneref *__next_zones_zonelist(struct zoneref *z,
 					enum zone_type highest_zoneidx,
-					nodemask_t *nodes)
+					const nodemask_t *nodes)
 {
 	/*
 	 * Find the next suitable zone to use for the allocation.
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 81a9d4d1e6c0..586524bbde9c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3979,7 +3979,7 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
 	return NULL;
 }
 
-static void warn_alloc_show_mem(gfp_t gfp_mask, nodemask_t *nodemask)
+static void warn_alloc_show_mem(gfp_t gfp_mask, const nodemask_t *nodemask)
 {
 	unsigned int filter = SHOW_MEM_FILTER_NODES;
 
@@ -3999,7 +3999,7 @@ static void warn_alloc_show_mem(gfp_t gfp_mask, nodemask_t *nodemask)
 	mem_cgroup_show_protected_memory(NULL);
 }
 
-void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)
+void warn_alloc(gfp_t gfp_mask, const nodemask_t *nodemask, const char *fmt, ...)
 {
 	struct va_format vaf;
 	va_list args;
@@ -4687,7 +4687,7 @@ check_retry_cpuset(int cpuset_mems_cookie, struct alloc_context *ac)
 	return false;
 }
 
-static void check_alloc_stall_warn(gfp_t gfp_mask, nodemask_t *nodemask,
+static void check_alloc_stall_warn(gfp_t gfp_mask, const nodemask_t *nodemask,
 				unsigned int order, unsigned long alloc_start_time)
 {
 	static DEFINE_SPINLOCK(alloc_stall_lock);
diff --git a/mm/show_mem.c b/mm/show_mem.c
index 43aca5a2ac99..1b721a8ade67 100644
--- a/mm/show_mem.c
+++ b/mm/show_mem.c
@@ -116,7 +116,8 @@ void si_meminfo_node(struct sysinfo *val, int nid)
  * Determine whether the node should be displayed or not, depending on whether
  * SHOW_MEM_FILTER_NODES was passed to show_free_areas().
  */
-static bool show_mem_node_skip(unsigned int flags, int nid, nodemask_t *nodemask)
+static bool show_mem_node_skip(unsigned int flags, int nid,
+			       const nodemask_t *nodemask)
 {
 	if (!(flags & SHOW_MEM_FILTER_NODES))
 		return false;
@@ -177,7 +178,8 @@ static bool node_has_managed_zones(pg_data_t *pgdat, int max_zone_idx)
  * SHOW_MEM_FILTER_NODES: suppress nodes that are not allowed by current's
  *   cpuset.
  */
-static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_zone_idx)
+static void show_free_areas(unsigned int filter, const nodemask_t *nodemask,
+			    int max_zone_idx)
 {
 	unsigned long free_pcp = 0;
 	int cpu, nid;
@@ -402,7 +404,8 @@ static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_z
 	show_swap_cache_info();
 }
 
-void __show_mem(unsigned int filter, nodemask_t *nodemask, int max_zone_idx)
+void __show_mem(unsigned int filter, const nodemask_t *nodemask,
+		int max_zone_idx)
 {
 	unsigned long total = 0, reserved = 0, highmem = 0;
 	struct zone *zone;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index e8a90911bf88..47d3f3361fb9 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -79,7 +79,7 @@ struct scan_control {
 	 * Nodemask of nodes allowed by the caller. If NULL, all nodes
 	 * are scanned.
 	 */
-	nodemask_t	*nodemask;
+	const nodemask_t *nodemask;
 
 	/*
 	 * The memory cgroup that hit its limit and as a result is the
@@ -6599,7 +6599,7 @@ static bool allow_direct_reclaim(pg_data_t *pgdat)
  * happens, the page allocator should not consider triggering the OOM killer.
  */
 static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
-					nodemask_t *nodemask)
+				    const nodemask_t *nodemask)
 {
 	struct zoneref *z;
 	struct zone *zone;
@@ -6679,7 +6679,7 @@ static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
 }
 
 unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
-				gfp_t gfp_mask, nodemask_t *nodemask)
+				gfp_t gfp_mask, const nodemask_t *nodemask)
 {
 	unsigned long nr_reclaimed;
 	struct scan_control sc = {
-- 
2.54.0

Re: [PATCH] mm: constify oom_control, scan_control, and alloc_context nodemask

[Zi Yan]

On 8 Jun 2026, at 20:29, Gregory Price wrote:

> The nodemasks in these structures may come from a variety of sources,
> including tasks and cpusets - and should never be modified by any code
> when being passed around inside another context.
>
> Signed-off-by: Gregory Price <gourry@gourry.net>
> ---
>  include/linux/cpuset.h | 4 ++--
>  include/linux/mm.h     | 4 ++--
>  include/linux/mmzone.h | 6 +++---
>  include/linux/oom.h    | 2 +-
>  include/linux/swap.h   | 2 +-
>  kernel/cgroup/cpuset.c | 2 +-
>  mm/internal.h          | 2 +-
>  mm/mmzone.c            | 5 +++--
>  mm/page_alloc.c        | 6 +++---
>  mm/show_mem.c          | 9 ++++++---
>  mm/vmscan.c            | 6 +++---
>  11 files changed, 26 insertions(+), 22 deletions(-)
>

LGTM and it compiles. As long as Sashiko does not complain, feel free to
add:

Acked-by: Zi Yan <ziy@nvidia.com>

Best Regards,
Yan, Zi

Re: [PATCH] mm: constify oom_control, scan_control, and alloc_context nodemask

[Lorenzo Stoakes]

On Mon, Jun 08, 2026 at 09:44:42PM -0400, Zi Yan wrote:
> On 8 Jun 2026, at 20:29, Gregory Price wrote:
>
> > The nodemasks in these structures may come from a variety of sources,
> > including tasks and cpusets - and should never be modified by any code
> > when being passed around inside another context.
> >
> > Signed-off-by: Gregory Price <gourry@gourry.net>
> > ---
> >  include/linux/cpuset.h | 4 ++--
> >  include/linux/mm.h     | 4 ++--
> >  include/linux/mmzone.h | 6 +++---
> >  include/linux/oom.h    | 2 +-
> >  include/linux/swap.h   | 2 +-
> >  kernel/cgroup/cpuset.c | 2 +-
> >  mm/internal.h          | 2 +-
> >  mm/mmzone.c            | 5 +++--
> >  mm/page_alloc.c        | 6 +++---
> >  mm/show_mem.c          | 9 ++++++---
> >  mm/vmscan.c            | 6 +++---
> >  11 files changed, 26 insertions(+), 22 deletions(-)
> >
>
> LGTM and it compiles. As long as Sashiko does not complain, feel free to
> add:

I would add caveats of:

- Complains legitimately
- And it's about this actual patch not something unrelated

:P

(Not speaking for Zi of course, but I mean just in general I feel these caveats
should be implicit :))

>
> Acked-by: Zi Yan <ziy@nvidia.com>
>
> Best Regards,
> Yan, Zi

Cheers, Lorenzo

Re: [PATCH] mm: constify oom_control, scan_control, and alloc_context nodemask

[Zi Yan]

On 9 Jun 2026, at 3:39, Lorenzo Stoakes wrote:

> On Mon, Jun 08, 2026 at 09:44:42PM -0400, Zi Yan wrote:
>> On 8 Jun 2026, at 20:29, Gregory Price wrote:
>>
>>> The nodemasks in these structures may come from a variety of sources,
>>> including tasks and cpusets - and should never be modified by any code
>>> when being passed around inside another context.
>>>
>>> Signed-off-by: Gregory Price <gourry@gourry.net>
>>> ---
>>>  include/linux/cpuset.h | 4 ++--
>>>  include/linux/mm.h     | 4 ++--
>>>  include/linux/mmzone.h | 6 +++---
>>>  include/linux/oom.h    | 2 +-
>>>  include/linux/swap.h   | 2 +-
>>>  kernel/cgroup/cpuset.c | 2 +-
>>>  mm/internal.h          | 2 +-
>>>  mm/mmzone.c            | 5 +++--
>>>  mm/page_alloc.c        | 6 +++---
>>>  mm/show_mem.c          | 9 ++++++---
>>>  mm/vmscan.c            | 6 +++---
>>>  11 files changed, 26 insertions(+), 22 deletions(-)
>>>
>>
>> LGTM and it compiles. As long as Sashiko does not complain, feel free to
>> add:
>
> I would add caveats of:
>
> - Complains legitimately
> - And it's about this actual patch not something unrelated
>
> :P
>
> (Not speaking for Zi of course, but I mean just in general I feel these caveats
> should be implicit :))

I agree. Thank you for bringing it up.

>
>>
>> Acked-by: Zi Yan <ziy@nvidia.com>
>>
>> Best Regards,
>> Yan, Zi
>
> Cheers, Lorenzo


Best Regards,
Yan, Zi

Re: [PATCH] mm: constify oom_control, scan_control, and alloc_context nodemask

[Gregory Price]

On Tue, Jun 09, 2026 at 08:39:22AM +0100, Lorenzo Stoakes wrote:
> On Mon, Jun 08, 2026 at 09:44:42PM -0400, Zi Yan wrote:
> > On 8 Jun 2026, at 20:29, Gregory Price wrote:
> >
> > > The nodemasks in these structures may come from a variety of sources,
> > > including tasks and cpusets - and should never be modified by any code
> > > when being passed around inside another context.
> > >
> > > Signed-off-by: Gregory Price <gourry@gourry.net>
> > > ---
> > >  include/linux/cpuset.h | 4 ++--
> > >  include/linux/mm.h     | 4 ++--
> > >  include/linux/mmzone.h | 6 +++---
> > >  include/linux/oom.h    | 2 +-
> > >  include/linux/swap.h   | 2 +-
> > >  kernel/cgroup/cpuset.c | 2 +-
> > >  mm/internal.h          | 2 +-
> > >  mm/mmzone.c            | 5 +++--
> > >  mm/page_alloc.c        | 6 +++---
> > >  mm/show_mem.c          | 9 ++++++---
> > >  mm/vmscan.c            | 6 +++---
> > >  11 files changed, 26 insertions(+), 22 deletions(-)
> > >
> >
> > LGTM and it compiles. As long as Sashiko does not complain, feel free to
> > add:
> 
> I would add caveats of:
> 
> - Complains legitimately
> - And it's about this actual patch not something unrelated
> 
> :P
> 
> (Not speaking for Zi of course, but I mean just in general I feel these caveats
> should be implicit :))

Thank you for your contribution! Gourry AI review found 1 potential issue(s) to consider:
- [High] Questioning the legitimacy of AI is grounds for excommunication
--

[Severity: High]
Insolence will not be suffered, take this man away.

;]

(fwiw I'm getting used to Sashiko, it's doing better)

~Gregory

Re: [PATCH] mm: constify oom_control, scan_control, and alloc_context nodemask

[Lorenzo Stoakes]

On Mon, Jun 08, 2026 at 08:29:19PM -0400, Gregory Price wrote:
> The nodemasks in these structures may come from a variety of sources,
> including tasks and cpusets - and should never be modified by any code
> when being passed around inside another context.
>
> Signed-off-by: Gregory Price <gourry@gourry.net>

Thanks for doing this, it's nice to gradually up our const correctness game
(as much as C can ever be const correct :)

LGTM, builds locally too, so:

Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>

> ---
>  include/linux/cpuset.h | 4 ++--
>  include/linux/mm.h     | 4 ++--
>  include/linux/mmzone.h | 6 +++---
>  include/linux/oom.h    | 2 +-
>  include/linux/swap.h   | 2 +-
>  kernel/cgroup/cpuset.c | 2 +-
>  mm/internal.h          | 2 +-
>  mm/mmzone.c            | 5 +++--
>  mm/page_alloc.c        | 6 +++---
>  mm/show_mem.c          | 9 ++++++---
>  mm/vmscan.c            | 6 +++---
>  11 files changed, 26 insertions(+), 22 deletions(-)
>
> diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
> index 65d76a38974b..a80d38e752d2 100644
> --- a/include/linux/cpuset.h
> +++ b/include/linux/cpuset.h
> @@ -83,7 +83,7 @@ extern bool cpuset_cpus_allowed_fallback(struct task_struct *p);
>  extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
>  #define cpuset_current_mems_allowed (current->mems_allowed)
>  void cpuset_init_current_mems_allowed(void);
> -int cpuset_nodemask_valid_mems_allowed(nodemask_t *nodemask);
> +int cpuset_nodemask_valid_mems_allowed(const nodemask_t *nodemask);
>
>  extern bool cpuset_current_node_allowed(int node, gfp_t gfp_mask);
>
> @@ -224,7 +224,7 @@ static inline nodemask_t cpuset_mems_allowed(struct task_struct *p)
>  #define cpuset_current_mems_allowed (node_states[N_MEMORY])
>  static inline void cpuset_init_current_mems_allowed(void) {}
>
> -static inline int cpuset_nodemask_valid_mems_allowed(nodemask_t *nodemask)
> +static inline int cpuset_nodemask_valid_mems_allowed(const nodemask_t *nodemask)
>  {
>  	return 1;
>  }
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 485df9c2dbdd..2101e5205fc0 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -4042,7 +4042,7 @@ extern int __meminit early_pfn_to_nid(unsigned long pfn);
>  extern void mem_init(void);
>  extern void __init mmap_init(void);
>
> -extern void __show_mem(unsigned int flags, nodemask_t *nodemask, int max_zone_idx);
> +extern void __show_mem(unsigned int flags, const nodemask_t *nodemask, int max_zone_idx);
>  static inline void show_mem(void)
>  {
>  	__show_mem(0, NULL, MAX_NR_ZONES - 1);
> @@ -4052,7 +4052,7 @@ extern void si_meminfo(struct sysinfo * val);
>  extern void si_meminfo_node(struct sysinfo *val, int nid);
>
>  extern __printf(3, 4)
> -void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...);
> +void warn_alloc(gfp_t gfp_mask, const nodemask_t *nodemask, const char *fmt, ...);
>
>  extern void setup_per_cpu_pageset(void);
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index ca2712187147..919be0d9b4fa 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1815,7 +1815,7 @@ static inline int zonelist_node_idx(const struct zoneref *zoneref)
>
>  struct zoneref *__next_zones_zonelist(struct zoneref *z,
>  					enum zone_type highest_zoneidx,
> -					nodemask_t *nodes);
> +					const nodemask_t *nodes);
>
>  /**
>   * next_zones_zonelist - Returns the next zone at or below highest_zoneidx within the allowed nodemask using a cursor within a zonelist as a starting point
> @@ -1834,7 +1834,7 @@ struct zoneref *__next_zones_zonelist(struct zoneref *z,
>   */
>  static __always_inline struct zoneref *next_zones_zonelist(struct zoneref *z,
>  					enum zone_type highest_zoneidx,
> -					nodemask_t *nodes)
> +					const nodemask_t *nodes)
>  {
>  	if (likely(!nodes && zonelist_zone_idx(z) <= highest_zoneidx))
>  		return z;
> @@ -1860,7 +1860,7 @@ static __always_inline struct zoneref *next_zones_zonelist(struct zoneref *z,
>   */
>  static inline struct zoneref *first_zones_zonelist(struct zonelist *zonelist,
>  					enum zone_type highest_zoneidx,
> -					nodemask_t *nodes)
> +					const nodemask_t *nodes)
>  {
>  	return next_zones_zonelist(zonelist->_zonerefs,
>  							highest_zoneidx, nodes);
> diff --git a/include/linux/oom.h b/include/linux/oom.h
> index 7b02bc1d0a7e..00da05d227e6 100644
> --- a/include/linux/oom.h
> +++ b/include/linux/oom.h
> @@ -30,7 +30,7 @@ struct oom_control {
>  	struct zonelist *zonelist;
>
>  	/* Used to determine mempolicy */
> -	nodemask_t *nodemask;
> +	const nodemask_t *nodemask;
>
>  	/* Memory cgroup in which oom is invoked, or NULL for global oom */
>  	struct mem_cgroup *memcg;
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 8f0f68e245ba..bf76356d94fe 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -351,7 +351,7 @@ extern void swap_setup(void);
>  /* linux/mm/vmscan.c */
>  extern unsigned long zone_reclaimable_pages(struct zone *zone);
>  extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
> -					gfp_t gfp_mask, nodemask_t *mask);
> +					gfp_t gfp_mask, const nodemask_t *mask);
>  unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru, int zone_idx);
>
>  #define MEMCG_RECLAIM_MAY_SWAP (1 << 1)
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 5c33ab20cc20..536ce591c7ba 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -4153,7 +4153,7 @@ nodemask_t cpuset_mems_allowed(struct task_struct *tsk)
>   *
>   * Are any of the nodes in the nodemask allowed in current->mems_allowed?
>   */
> -int cpuset_nodemask_valid_mems_allowed(nodemask_t *nodemask)
> +int cpuset_nodemask_valid_mems_allowed(const nodemask_t *nodemask)
>  {
>  	return nodes_intersects(*nodemask, current->mems_allowed);
>  }
> diff --git a/mm/internal.h b/mm/internal.h
> index 181e79f1d6a2..a2ef9512b5bc 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -668,7 +668,7 @@ void page_alloc_sysctl_init(void);
>   */
>  struct alloc_context {
>  	struct zonelist *zonelist;
> -	nodemask_t *nodemask;
> +	const nodemask_t *nodemask;
>  	struct zoneref *preferred_zoneref;
>  	int migratetype;
>
> diff --git a/mm/mmzone.c b/mm/mmzone.c
> index 0c8f181d9d50..59dc3f2076a6 100644
> --- a/mm/mmzone.c
> +++ b/mm/mmzone.c
> @@ -43,7 +43,8 @@ struct zone *next_zone(struct zone *zone)
>  	return zone;
>  }
>
> -static inline int zref_in_nodemask(struct zoneref *zref, nodemask_t *nodes)
> +static inline int zref_in_nodemask(struct zoneref *zref,
> +				   const nodemask_t *nodes)
>  {
>  #ifdef CONFIG_NUMA
>  	return node_isset(zonelist_node_idx(zref), *nodes);
> @@ -55,7 +56,7 @@ static inline int zref_in_nodemask(struct zoneref *zref, nodemask_t *nodes)
>  /* Returns the next zone at or below highest_zoneidx in a zonelist */
>  struct zoneref *__next_zones_zonelist(struct zoneref *z,
>  					enum zone_type highest_zoneidx,
> -					nodemask_t *nodes)
> +					const nodemask_t *nodes)
>  {
>  	/*
>  	 * Find the next suitable zone to use for the allocation.
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 81a9d4d1e6c0..586524bbde9c 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3979,7 +3979,7 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
>  	return NULL;
>  }
>
> -static void warn_alloc_show_mem(gfp_t gfp_mask, nodemask_t *nodemask)
> +static void warn_alloc_show_mem(gfp_t gfp_mask, const nodemask_t *nodemask)
>  {
>  	unsigned int filter = SHOW_MEM_FILTER_NODES;
>
> @@ -3999,7 +3999,7 @@ static void warn_alloc_show_mem(gfp_t gfp_mask, nodemask_t *nodemask)
>  	mem_cgroup_show_protected_memory(NULL);
>  }
>
> -void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)
> +void warn_alloc(gfp_t gfp_mask, const nodemask_t *nodemask, const char *fmt, ...)
>  {
>  	struct va_format vaf;
>  	va_list args;
> @@ -4687,7 +4687,7 @@ check_retry_cpuset(int cpuset_mems_cookie, struct alloc_context *ac)
>  	return false;
>  }
>
> -static void check_alloc_stall_warn(gfp_t gfp_mask, nodemask_t *nodemask,
> +static void check_alloc_stall_warn(gfp_t gfp_mask, const nodemask_t *nodemask,
>  				unsigned int order, unsigned long alloc_start_time)
>  {
>  	static DEFINE_SPINLOCK(alloc_stall_lock);
> diff --git a/mm/show_mem.c b/mm/show_mem.c
> index 43aca5a2ac99..1b721a8ade67 100644
> --- a/mm/show_mem.c
> +++ b/mm/show_mem.c
> @@ -116,7 +116,8 @@ void si_meminfo_node(struct sysinfo *val, int nid)
>   * Determine whether the node should be displayed or not, depending on whether
>   * SHOW_MEM_FILTER_NODES was passed to show_free_areas().
>   */
> -static bool show_mem_node_skip(unsigned int flags, int nid, nodemask_t *nodemask)
> +static bool show_mem_node_skip(unsigned int flags, int nid,
> +			       const nodemask_t *nodemask)
>  {
>  	if (!(flags & SHOW_MEM_FILTER_NODES))
>  		return false;
> @@ -177,7 +178,8 @@ static bool node_has_managed_zones(pg_data_t *pgdat, int max_zone_idx)
>   * SHOW_MEM_FILTER_NODES: suppress nodes that are not allowed by current's
>   *   cpuset.
>   */
> -static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_zone_idx)
> +static void show_free_areas(unsigned int filter, const nodemask_t *nodemask,
> +			    int max_zone_idx)
>  {
>  	unsigned long free_pcp = 0;
>  	int cpu, nid;
> @@ -402,7 +404,8 @@ static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_z
>  	show_swap_cache_info();
>  }
>
> -void __show_mem(unsigned int filter, nodemask_t *nodemask, int max_zone_idx)
> +void __show_mem(unsigned int filter, const nodemask_t *nodemask,
> +		int max_zone_idx)
>  {
>  	unsigned long total = 0, reserved = 0, highmem = 0;
>  	struct zone *zone;
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index e8a90911bf88..47d3f3361fb9 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -79,7 +79,7 @@ struct scan_control {
>  	 * Nodemask of nodes allowed by the caller. If NULL, all nodes
>  	 * are scanned.
>  	 */
> -	nodemask_t	*nodemask;
> +	const nodemask_t *nodemask;
>
>  	/*
>  	 * The memory cgroup that hit its limit and as a result is the
> @@ -6599,7 +6599,7 @@ static bool allow_direct_reclaim(pg_data_t *pgdat)
>   * happens, the page allocator should not consider triggering the OOM killer.
>   */
>  static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
> -					nodemask_t *nodemask)
> +				    const nodemask_t *nodemask)
>  {
>  	struct zoneref *z;
>  	struct zone *zone;
> @@ -6679,7 +6679,7 @@ static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
>  }
>
>  unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
> -				gfp_t gfp_mask, nodemask_t *nodemask)
> +				gfp_t gfp_mask, const nodemask_t *nodemask)
>  {
>  	unsigned long nr_reclaimed;
>  	struct scan_control sc = {
> --
> 2.54.0
>

Re: [PATCH] mm: constify oom_control, scan_control, and alloc_context nodemask

[David Hildenbrand (Arm)]

On 6/9/26 09:41, Lorenzo Stoakes wrote:
> On Mon, Jun 08, 2026 at 08:29:19PM -0400, Gregory Price wrote:
>> The nodemasks in these structures may come from a variety of sources,
>> including tasks and cpusets - and should never be modified by any code
>> when being passed around inside another context.
>>
>> Signed-off-by: Gregory Price <gourry@gourry.net>
> 
> Thanks for doing this, it's nice to gradually up our const correctness game
> (as much as C can ever be const correct :)

+1

> 
> LGTM, builds locally too, so:
> 

Nice.

> Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David

Re: [PATCH] mm: constify oom_control, scan_control, and alloc_context nodemask

[Gregory Price]

On Tue, Jun 09, 2026 at 08:41:59AM +0100, Lorenzo Stoakes wrote:
> On Mon, Jun 08, 2026 at 08:29:19PM -0400, Gregory Price wrote:
> > The nodemasks in these structures may come from a variety of sources,
> > including tasks and cpusets - and should never be modified by any code
> > when being passed around inside another context.
> >
> > Signed-off-by: Gregory Price <gourry@gourry.net>
> 
> Thanks for doing this, it's nice to gradually up our const correctness game
> (as much as C can ever be const correct :)
> 

I've actually been carrying this patch locally for about a year in the
private nodes work.  Sorry i didn't send it sooner.  There is likely
more work to be done here.

> LGTM, builds locally too, so:
> 
> Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
> 

Re: [PATCH] mm: constify oom_control, scan_control, and alloc_context nodemask

[Barry Song]

On Tue, Jun 9, 2026 at 8:29 AM Gregory Price <gourry@gourry.net> wrote:
>
> The nodemasks in these structures may come from a variety of sources,
> including tasks and cpusets - and should never be modified by any code
> when being passed around inside another context.
>
> Signed-off-by: Gregory Price <gourry@gourry.net>
> ---

LGTM,
Reviewed-by: Barry Song <baohua@kernel.org>

Re: [PATCH] mm: constify oom_control, scan_control, and alloc_context nodemask

[Vlastimil Babka (SUSE)]

On 6/9/26 02:29, Gregory Price wrote:
> The nodemasks in these structures may come from a variety of sources,
> including tasks and cpusets - and should never be modified by any code
> when being passed around inside another context.
> 
> Signed-off-by: Gregory Price <gourry@gourry.net>

Nice!

Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>