Re: [PATCH 02/14] fs: Make page_mkwrite_check_truncate thp-aware

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Wed, Oct 14, 2020 at 04:03:45AM +0100, Matthew Wilcox (Oracle) wrote:
> If the page is compound, check the last index in the page and return
> the appropriate size.  Change the return type to ssize_t in case we ever
> support pages larger than 2GB.

"But what about 16G pages?" :P

> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>  include/linux/pagemap.h | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 7dc6bf713d27..5083a0efafa8 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -983,22 +983,22 @@ static inline unsigned long dir_pages(struct inode *inode)
>   * @page: the page to check
>   * @inode: the inode to check the page against
>   *
> - * Returns the number of bytes in the page up to EOF,
> + * Return: The number of bytes in the page up to EOF,
>   * or -EFAULT if the page was truncated.
>   */
> -static inline int page_mkwrite_check_truncate(struct page *page,
> +static inline ssize_t page_mkwrite_check_truncate(struct page *page,
>  					      struct inode *inode)
>  {
>  	loff_t size = i_size_read(inode);
>  	pgoff_t index = size >> PAGE_SHIFT;
> -	int offset = offset_in_page(size);
> +	unsigned long offset = offset_in_thp(page, size);
>  
>  	if (page->mapping != inode->i_mapping)
>  		return -EFAULT;
>  
>  	/* page is wholly inside EOF */
> -	if (page->index < index)
> -		return PAGE_SIZE;
> +	if (page->index + thp_nr_pages(page) - 1 < index)

Just curious, is this expression common enough to create a helper for
that too?

#define thp_last_index(page) ((page)->index + thp_nr_pages(page) - 1) ?

(Maybe make that a static inline, I used a macro for brevity)

Otherwise looks fine to me...

--D

> +		return thp_size(page);
>  	/* page is wholly past EOF */
>  	if (page->index > index || !offset)
>  		return -EFAULT;
> -- 
> 2.28.0
>