Re: [PATCH v9 09/17] mm: uninline the main body of vma_start_write()

[Lorenzo Stoakes]

On Fri, Jan 10, 2025 at 08:25:56PM -0800, Suren Baghdasaryan wrote:
> vma_start_write() is used in many places and will grow in size very soon.
> It is not used in performance critical paths and uninlining it should
> limit the future code size growth.
> No functional changes.
>
> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>

LGTM,

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>

> ---
>  include/linux/mm.h | 12 +++---------
>  mm/memory.c        | 14 ++++++++++++++
>  2 files changed, 17 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index cbb4e3dbbaed..3432756d95e6 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -787,6 +787,8 @@ static bool __is_vma_write_locked(struct vm_area_struct *vma, unsigned int *mm_l
>  	return (vma->vm_lock_seq == *mm_lock_seq);
>  }
>
> +void __vma_start_write(struct vm_area_struct *vma, unsigned int mm_lock_seq);
> +
>  /*
>   * Begin writing to a VMA.
>   * Exclude concurrent readers under the per-VMA lock until the currently
> @@ -799,15 +801,7 @@ static inline void vma_start_write(struct vm_area_struct *vma)
>  	if (__is_vma_write_locked(vma, &mm_lock_seq))
>  		return;
>
> -	down_write(&vma->vm_lock.lock);
> -	/*
> -	 * We should use WRITE_ONCE() here because we can have concurrent reads
> -	 * from the early lockless pessimistic check in vma_start_read().
> -	 * We don't really care about the correctness of that early check, but
> -	 * we should use WRITE_ONCE() for cleanliness and to keep KCSAN happy.
> -	 */
> -	WRITE_ONCE(vma->vm_lock_seq, mm_lock_seq);
> -	up_write(&vma->vm_lock.lock);
> +	__vma_start_write(vma, mm_lock_seq);
>  }
>
>  static inline void vma_assert_write_locked(struct vm_area_struct *vma)
> diff --git a/mm/memory.c b/mm/memory.c
> index d0dee2282325..236fdecd44d6 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -6328,6 +6328,20 @@ struct vm_area_struct *lock_mm_and_find_vma(struct mm_struct *mm,
>  #endif
>
>  #ifdef CONFIG_PER_VMA_LOCK
> +void __vma_start_write(struct vm_area_struct *vma, unsigned int mm_lock_seq)
> +{
> +	down_write(&vma->vm_lock.lock);
> +	/*
> +	 * We should use WRITE_ONCE() here because we can have concurrent reads
> +	 * from the early lockless pessimistic check in vma_start_read().
> +	 * We don't really care about the correctness of that early check, but
> +	 * we should use WRITE_ONCE() for cleanliness and to keep KCSAN happy.
> +	 */
> +	WRITE_ONCE(vma->vm_lock_seq, mm_lock_seq);
> +	up_write(&vma->vm_lock.lock);
> +}
> +EXPORT_SYMBOL_GPL(__vma_start_write);
> +
>  /*
>   * Lookup and lock a VMA under RCU protection. Returned VMA is guaranteed to be
>   * stable and not isolated. If the VMA is not found or is being modified the
> --
> 2.47.1.613.gc27f4b7a9f-goog
>