[PATCH v3 0/2] Two small patches to clean up mm/mm_slot.h

[PATCH v3 0/2] Two small patches to clean up mm/mm_slot.h

[xu.xin16]

From: xu xin <xu.xin16@zte.com.cn>

mm_slot.h is mainly used by THP and KSM.

Patch 1 introduces mm_slot_remove() to abstract the common
hash_del() + list_del() sequence used in both khugepaged and KSM.

Patch 2 adds a comment explaining why mm_slot_lookup/insert cannot
be converted to static inline functions.

xu xin (2):
  mm/mm_slot.h: add a helper function mm_slot_remove
  mm/mm_slot.h: add comments for mm_slot_lookup/insert

 mm/khugepaged.c |  6 ++----
 mm/ksm.c        |  9 +++------
 mm/mm_slot.h    | 11 +++++++++++
 3 files changed, 16 insertions(+), 10 deletions(-)

-- 
2.25.1

[PATCH v3 1/2] mm/mm_slot.h: add a helper function mm_slot_remove

[xu.xin16]

From: xu xin <xu.xin16@zte.com.cn>

Both THP and KSM manage per-mm scanning slots using the mm_slot
structure. The slot is kept in a hash table and a list, and removal from
both containers requires the same two operations: hash_del() and
list_del().

Introduce mm_slot_remove() to abstract the common hash_del() + list_del()
sequence used in both khugepaged and KSM.

No functional change is intended.

Signed-off-by: xu xin <xu.xin16@zte.com.cn>
Reviewed-by: Nico Pache <npache@redhat.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: SJ Park <sj@kernel.org>
---
 mm/khugepaged.c | 6 ++----
 mm/ksm.c        | 9 +++------
 mm/mm_slot.h    | 5 +++++
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 58e14d1543ec..5f6eb1bd9a67 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -606,8 +606,7 @@ void __khugepaged_exit(struct mm_struct *mm)
 	spin_lock(&khugepaged_mm_lock);
 	slot = mm_slot_lookup(mm_slots_hash, mm);
 	if (slot && khugepaged_scan.mm_slot != slot) {
-		hash_del(&slot->hash);
-		list_del(&slot->mm_node);
+		mm_slot_remove(slot);
 		free = 1;
 	}
 	spin_unlock(&khugepaged_mm_lock);
@@ -1802,8 +1801,7 @@ static void collect_mm_slot(struct mm_slot *slot)

 	if (collapse_test_exit(mm)) {
 		/* free mm_slot */
-		hash_del(&slot->hash);
-		list_del(&slot->mm_node);
+		mm_slot_remove(slot);

 		/*
 		 * Not strictly needed because the mm exited already.
diff --git a/mm/ksm.c b/mm/ksm.c
index 2791ce5bd44b..443dab513da6 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1257,8 +1257,7 @@ static int unmerge_and_remove_all_rmap_items(void)
 				  struct mm_slot, mm_node);
 		ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
 		if (ksm_test_exit(mm)) {
-			hash_del(&mm_slot->slot.hash);
-			list_del(&mm_slot->slot.mm_node);
+			mm_slot_remove(&mm_slot->slot);
 			spin_unlock(&ksm_mmlist_lock);

 			mm_slot_free(mm_slot_cache, mm_slot);
@@ -2772,8 +2771,7 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
 		 * or when all VM_MERGEABLE areas have been unmapped (and
 		 * mmap_lock then protects against race with MADV_MERGEABLE).
 		 */
-		hash_del(&mm_slot->slot.hash);
-		list_del(&mm_slot->slot.mm_node);
+		mm_slot_remove(&mm_slot->slot);
 		spin_unlock(&ksm_mmlist_lock);

 		mm_slot_free(mm_slot_cache, mm_slot);
@@ -3116,8 +3114,7 @@ void __ksm_exit(struct mm_struct *mm)
 	if (ksm_scan.mm_slot == mm_slot)
 		goto unlock;
 	if (!mm_slot->rmap_list) {
-		hash_del(&slot->hash);
-		list_del(&slot->mm_node);
+		mm_slot_remove(slot);
 		easy_to_free = 1;
 	} else {
 		list_move(&slot->mm_node,
diff --git a/mm/mm_slot.h b/mm/mm_slot.h
index 83f18ed1c4bd..5de3e91d86b4 100644
--- a/mm/mm_slot.h
+++ b/mm/mm_slot.h
@@ -52,4 +52,9 @@ static inline void mm_slot_free(struct kmem_cache *cache, void *objp)
 	hash_add(_hashtable, &_mm_slot->hash, (unsigned long)_mm);	       \
 })

+static inline void mm_slot_remove(struct mm_slot *slot)
+{
+	hash_del(&slot->hash);
+	list_del(&slot->mm_node);
+}
 #endif /* _LINUX_MM_SLOT_H */
-- 
2.25.1

[PATCH v3 2/2] mm/mm_slot.h: add comments for mm_slot_lookup/insert

[xu.xin16]

From: xu xin <xu.xin16@zte.com.cn>

mm_slot_lookup() and mm_slot_insert() are the only helpers in
this header that are implemented as macros rather than static inline
functions. This may look inconsistent without explanation.

Explain they must be macros because hash_for_each_possible()
needs the table as an array (for sizeof), not a pointer.

Signed-off-by: xu xin <xu.xin16@zte.com.cn>
---
 mm/mm_slot.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/mm_slot.h b/mm/mm_slot.h
index 5de3e91d86b4..9b09b68e5742 100644
--- a/mm/mm_slot.h
+++ b/mm/mm_slot.h
@@ -33,6 +33,12 @@ static inline void mm_slot_free(struct kmem_cache *cache, void *objp)
 	kmem_cache_free(cache, objp);
 }

+/*
+ * Note: mm_slot_lookup and mm_slot_insert cannot be converted to static inline
+ * functions because the hash helpers (hash_for_each_possible and hash_add) rely
+ * on the actual array argument 'hashtable' for sizeof() instead of pointers.
+ */
+
 #define mm_slot_lookup(_hashtable, _mm) 				       \
 ({									       \
 	struct mm_slot *tmp_slot, *mm_slot = NULL;			       \
-- 
2.25.1

Re: [PATCH v3 2/2] mm/mm_slot.h: add comments for mm_slot_lookup/insert

[Barry Song]

On Tue, Jul 14, 2026 at 9:28 AM <xu.xin16@zte.com.cn> wrote:
>
> From: xu xin <xu.xin16@zte.com.cn>
>
> mm_slot_lookup() and mm_slot_insert() are the only helpers in
> this header that are implemented as macros rather than static inline
> functions. This may look inconsistent without explanation.
>
> Explain they must be macros because hash_for_each_possible()
> needs the table as an array (for sizeof), not a pointer.
>
> Signed-off-by: xu xin <xu.xin16@zte.com.cn>

Thanks!

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

Re: [PATCH v3 2/2] mm/mm_slot.h: add comments for mm_slot_lookup/insert

[Lorenzo Stoakes (ARM)]

On Tue, Jul 14, 2026 at 09:28:15AM +0800, xu.xin16@zte.com.cn wrote:
> From: xu xin <xu.xin16@zte.com.cn>
>
> mm_slot_lookup() and mm_slot_insert() are the only helpers in
> this header that are implemented as macros rather than static inline
> functions. This may look inconsistent without explanation.
>
> Explain they must be macros because hash_for_each_possible()
> needs the table as an array (for sizeof), not a pointer.
>
> Signed-off-by: xu xin <xu.xin16@zte.com.cn>

LGTM, so:

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

> ---
>  mm/mm_slot.h | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/mm/mm_slot.h b/mm/mm_slot.h
> index 5de3e91d86b4..9b09b68e5742 100644
> --- a/mm/mm_slot.h
> +++ b/mm/mm_slot.h
> @@ -33,6 +33,12 @@ static inline void mm_slot_free(struct kmem_cache *cache, void *objp)
>  	kmem_cache_free(cache, objp);
>  }
>
> +/*
> + * Note: mm_slot_lookup and mm_slot_insert cannot be converted to static inline
> + * functions because the hash helpers (hash_for_each_possible and hash_add) rely
> + * on the actual array argument 'hashtable' for sizeof() instead of pointers.
> + */
> +
>  #define mm_slot_lookup(_hashtable, _mm) 				       \
>  ({									       \
>  	struct mm_slot *tmp_slot, *mm_slot = NULL;			       \
> --
> 2.25.1

Re: [PATCH v3 2/2] mm/mm_slot.h: add comments for mm_slot_lookup/insert

[Qi Zheng]

On 7/14/26 9:28 AM, xu.xin16@zte.com.cn wrote:
> From: xu xin <xu.xin16@zte.com.cn>
> 
> mm_slot_lookup() and mm_slot_insert() are the only helpers in
> this header that are implemented as macros rather than static inline
> functions. This may look inconsistent without explanation.
> 
> Explain they must be macros because hash_for_each_possible()
> needs the table as an array (for sizeof), not a pointer.
> 
> Signed-off-by: xu xin <xu.xin16@zte.com.cn>
> ---
>   mm/mm_slot.h | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/mm/mm_slot.h b/mm/mm_slot.h
> index 5de3e91d86b4..9b09b68e5742 100644
> --- a/mm/mm_slot.h
> +++ b/mm/mm_slot.h
> @@ -33,6 +33,12 @@ static inline void mm_slot_free(struct kmem_cache *cache, void *objp)
>   	kmem_cache_free(cache, objp);
>   }
> 
> +/*
> + * Note: mm_slot_lookup and mm_slot_insert cannot be converted to static inline
> + * functions because the hash helpers (hash_for_each_possible and hash_add) rely
> + * on the actual array argument 'hashtable' for sizeof() instead of pointers.
> + */

Right, that's why I wrote them as macros to begin with.

Reviewed-by: Qi Zheng <qi.zheng@linux.dev>

Thanks,
Qi

> +
>   #define mm_slot_lookup(_hashtable, _mm) 				       \
>   ({									       \
>   	struct mm_slot *tmp_slot, *mm_slot = NULL;			       \

Re: [PATCH v3 2/2] mm/mm_slot.h: add comments for mm_slot_lookup/insert

[David Hildenbrand (Arm)]

On 7/14/26 03:28, xu.xin16@zte.com.cn wrote:
> From: xu xin <xu.xin16@zte.com.cn>
> 
> mm_slot_lookup() and mm_slot_insert() are the only helpers in
> this header that are implemented as macros rather than static inline
> functions. This may look inconsistent without explanation.
> 
> Explain they must be macros because hash_for_each_possible()
> needs the table as an array (for sizeof), not a pointer.
> 
> Signed-off-by: xu xin <xu.xin16@zte.com.cn>
> ---

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

-- 
Cheers,

David

Re: [PATCH v3 2/2] mm/mm_slot.h: add comments for mm_slot_lookup/insert

[SJ Park]

On Tue, 14 Jul 2026 09:28:15 +0800 (CST) <xu.xin16@zte.com.cn> wrote:

> From: xu xin <xu.xin16@zte.com.cn>
> 
> mm_slot_lookup() and mm_slot_insert() are the only helpers in
> this header that are implemented as macros rather than static inline
> functions. This may look inconsistent without explanation.
> 
> Explain they must be macros because hash_for_each_possible()
> needs the table as an array (for sizeof), not a pointer.

Thank you for adding the explanation!

> 
> Signed-off-by: xu xin <xu.xin16@zte.com.cn>

Reviewed-by: SJ Park <sj@kernel.org>


Thanks,
SJ

[...]

Re: [PATCH v3 2/2] mm/mm_slot.h: add comments for mm_slot_lookup/insert

[Zi Yan]

On Mon Jul 13, 2026 at 9:28 PM EDT,  wrote:
> From: xu xin <xu.xin16@zte.com.cn>
>
> mm_slot_lookup() and mm_slot_insert() are the only helpers in
> this header that are implemented as macros rather than static inline
> functions. This may look inconsistent without explanation.
>
> Explain they must be macros because hash_for_each_possible()
> needs the table as an array (for sizeof), not a pointer.
>
> Signed-off-by: xu xin <xu.xin16@zte.com.cn>
> ---
>  mm/mm_slot.h | 6 ++++++
>  1 file changed, 6 insertions(+)
>
LGTM. Thanks.

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


-- 
Best Regards,
Yan, Zi