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

[Qi Zheng <qi.zheng@linux.dev>]

Hi Wei,

On 2/22/26 8:45 AM, Wei Yang 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.

Thank you for doing this, but we can't do it right now.

See the latest version: 
https://github.com/torvalds/linux/commit/9c8c02df3f8742f6db927e787ab971fd0b5ac08a, 
when the
HAVE_ARCH_TLB_REMOVE_TABLE is selected, the pt_rcu_head member
cannot be used.

Thanks,
Qi

> 
> 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;