[PATCH] mm/mmu_gather: define RCU version tlb_remove_table_one() in CONFIG_MMU_GATHER_RCU_TABLE_FREE

[PATCH] mm/mmu_gather: define RCU version tlb_remove_table_one() in CONFIG_MMU_GATHER_RCU_TABLE_FREE

[Wei Yang]

Before commit 718b13861d22 ("x86: mm: free page table pages by RCU
instead of semi RCU"), the page table pages will be freed by semi RCU,
that is:

  - batch table freeing: asynchronous free by RCU
  - single table freeing: IPI + synchronous free

This commit introduce a RCU version for single table freeing to support
PT_RECLAIM. While it is not necessary to limit the RCU version only in
CONFIG_PT_RECLAIM. It is reasonable to asynchronous free single table by
RCU if CONFIG_MMU_GATHER_RCU_TABLE_FREE.

This patch moves the definition of single table freeing in
CONFIG_MMU_GATHER_RCU_TABLE_FREE, so we have both RCU version
batch/single table freeing if CONFIG_MMU_GATHER_RCU_TABLE_FREE.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Qi Zheng <qi.zheng@linux.dev>
Cc: "David Hildenbrand (Arm)" <david@kernel.org>
---
 mm/mmu_gather.c | 51 +++++++++++++++++++++----------------------------
 1 file changed, 22 insertions(+), 29 deletions(-)

diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
index fe5b6a031717..6c1cbd9c717b 100644
--- a/mm/mmu_gather.c
+++ b/mm/mmu_gather.c
@@ -296,6 +296,22 @@ static void tlb_remove_table_free(struct mmu_table_batch *batch)
 	call_rcu(&batch->rcu, tlb_remove_table_rcu);
 }
 
+static inline void __tlb_remove_table_one_rcu(struct rcu_head *head)
+{
+	struct ptdesc *ptdesc;
+
+	ptdesc = container_of(head, struct ptdesc, pt_rcu_head);
+	__tlb_remove_table(ptdesc);
+}
+
+static inline void tlb_remove_table_one(void *table)
+{
+	struct ptdesc *ptdesc;
+
+	ptdesc = table;
+	call_rcu(&ptdesc->pt_rcu_head, __tlb_remove_table_one_rcu);
+}
+
 #else /* !CONFIG_MMU_GATHER_RCU_TABLE_FREE */
 
 static void tlb_remove_table_free(struct mmu_table_batch *batch)
@@ -303,6 +319,12 @@ static void tlb_remove_table_free(struct mmu_table_batch *batch)
 	__tlb_remove_table_free(batch);
 }
 
+static inline void tlb_remove_table_one(void *table)
+{
+	tlb_remove_table_sync_one();
+	__tlb_remove_table(table);
+}
+
 #endif /* CONFIG_MMU_GATHER_RCU_TABLE_FREE */
 
 /*
@@ -320,35 +342,6 @@ static inline void tlb_table_invalidate(struct mmu_gather *tlb)
 	}
 }
 
-#ifdef CONFIG_PT_RECLAIM
-static inline void __tlb_remove_table_one_rcu(struct rcu_head *head)
-{
-	struct ptdesc *ptdesc;
-
-	ptdesc = container_of(head, struct ptdesc, pt_rcu_head);
-	__tlb_remove_table(ptdesc);
-}
-
-static inline void __tlb_remove_table_one(void *table)
-{
-	struct ptdesc *ptdesc;
-
-	ptdesc = table;
-	call_rcu(&ptdesc->pt_rcu_head, __tlb_remove_table_one_rcu);
-}
-#else
-static inline void __tlb_remove_table_one(void *table)
-{
-	tlb_remove_table_sync_one();
-	__tlb_remove_table(table);
-}
-#endif /* CONFIG_PT_RECLAIM */
-
-static void tlb_remove_table_one(void *table)
-{
-	__tlb_remove_table_one(table);
-}
-
 static void tlb_table_flush(struct mmu_gather *tlb)
 {
 	struct mmu_table_batch **batch = &tlb->batch;
-- 
2.34.1

Re: [PATCH] mm/mmu_gather: define RCU version tlb_remove_table_one() in CONFIG_MMU_GATHER_RCU_TABLE_FREE

[Andrew Morton]

On Sun, 22 Feb 2026 00:45:12 +0000 Wei Yang <richard.weiyang@gmail.com> wrote:

> Before commit 718b13861d22 ("x86: mm: free page table pages by RCU
> instead of semi RCU"), the page table pages will be freed by semi RCU,
> that is:
> 
>   - batch table freeing: asynchronous free by RCU
>   - single table freeing: IPI + synchronous free
> 
> This commit introduce a RCU version for single table freeing to support
> PT_RECLAIM. While it is not necessary to limit the RCU version only in
> CONFIG_PT_RECLAIM. It is reasonable to asynchronous free single table by
> RCU if CONFIG_MMU_GATHER_RCU_TABLE_FREE.
> 
> This patch moves the definition of single table freeing in
> CONFIG_MMU_GATHER_RCU_TABLE_FREE, so we have both RCU version
> batch/single table freeing if CONFIG_MMU_GATHER_RCU_TABLE_FREE.

What are the expected (and measured!) benefits of this?