Re: [PATCH v4 3/4] mm: Drop first_index/last_index in zap_details

[Hugh Dickins]

On Wed, 15 Sep 2021, Peter Xu wrote:

> The first_index/last_index parameters in zap_details are actually only used in
> unmap_mapping_range_tree().  At the meantime, this function is only called by
> unmap_mapping_pages() once.  Instead of passing these two variables through the
> whole stack of page zapping code, remove them from zap_details and let them
> simply be parameters of unmap_mapping_range_tree(), which is inlined.
> 
> Reviewed-by: Alistair Popple <apopple@xxxxxxxxxx>
> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
> Reviewed-by: Liam Howlett <liam.howlett@xxxxxxxxxx>
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>

And this one is fine too, thanks.  I don't know whether it saves anything
(ah yes, with args in registers not on the stack, should save a little),
but it's helpful to limit the scope of those indices.

You may wonder how they came to be in zap_details: that dates from the
days of remap_file_pages(): nonlinear vmas, in which the zapper needed
to check each pte_file()'s offset against first and last index, to
decide whether to zap or not.  They should have been removed in 4.0.

Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>

> ---
>  include/linux/mm.h |  2 --
>  mm/memory.c        | 31 ++++++++++++++++++-------------
>  2 files changed, 18 insertions(+), 15 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 73a52aba448f..d1126f731221 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1722,8 +1722,6 @@ extern void user_shm_unlock(size_t, struct ucounts *);
>   */
>  struct zap_details {
>  	struct address_space *check_mapping;	/* Check page->mapping if set */
> -	pgoff_t	first_index;			/* Lowest page->index to unmap */
> -	pgoff_t last_index;			/* Highest page->index to unmap */
>  	struct page *single_page;		/* Locked page to be unmapped */
>  };
>  
> diff --git a/mm/memory.c b/mm/memory.c
> index 7b095f07c4ef..a7e427177817 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3321,20 +3321,20 @@ static void unmap_mapping_range_vma(struct vm_area_struct *vma,
>  }
>  
>  static inline void unmap_mapping_range_tree(struct rb_root_cached *root,
> +					    pgoff_t first_index,
> +					    pgoff_t last_index,
>  					    struct zap_details *details)
>  {
>  	struct vm_area_struct *vma;
>  	pgoff_t vba, vea, zba, zea;
>  
> -	vma_interval_tree_foreach(vma, root,
> -			details->first_index, details->last_index) {
> -
> +	vma_interval_tree_foreach(vma, root, first_index, last_index) {
>  		vba = vma->vm_pgoff;
>  		vea = vba + vma_pages(vma) - 1;
> -		zba = details->first_index;
> +		zba = first_index;
>  		if (zba < vba)
>  			zba = vba;
> -		zea = details->last_index;
> +		zea = last_index;
>  		if (zea > vea)
>  			zea = vea;
>  
> @@ -3360,18 +3360,22 @@ void unmap_mapping_page(struct page *page)
>  {
>  	struct address_space *mapping = page->mapping;
>  	struct zap_details details = { };
> +	pgoff_t	first_index;
> +	pgoff_t	last_index;
>  
>  	VM_BUG_ON(!PageLocked(page));
>  	VM_BUG_ON(PageTail(page));
>  
> +	first_index = page->index;
> +	last_index = page->index + thp_nr_pages(page) - 1;
> +
>  	details.check_mapping = mapping;
> -	details.first_index = page->index;
> -	details.last_index = page->index + thp_nr_pages(page) - 1;
>  	details.single_page = page;
>  
>  	i_mmap_lock_write(mapping);
>  	if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root)))
> -		unmap_mapping_range_tree(&mapping->i_mmap, &details);
> +		unmap_mapping_range_tree(&mapping->i_mmap, first_index,
> +					 last_index, &details);
>  	i_mmap_unlock_write(mapping);
>  }
>  
> @@ -3391,16 +3395,17 @@ void unmap_mapping_pages(struct address_space *mapping, pgoff_t start,
>  		pgoff_t nr, bool even_cows)
>  {
>  	struct zap_details details = { };
> +	pgoff_t	first_index = start;
> +	pgoff_t	last_index = start + nr - 1;
>  
>  	details.check_mapping = even_cows ? NULL : mapping;
> -	details.first_index = start;
> -	details.last_index = start + nr - 1;
> -	if (details.last_index < details.first_index)
> -		details.last_index = ULONG_MAX;
> +	if (last_index < first_index)
> +		last_index = ULONG_MAX;
>  
>  	i_mmap_lock_write(mapping);
>  	if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root)))
> -		unmap_mapping_range_tree(&mapping->i_mmap, &details);
> +		unmap_mapping_range_tree(&mapping->i_mmap, first_index,
> +					 last_index, &details);
>  	i_mmap_unlock_write(mapping);
>  }
>  
> -- 
> 2.31.1