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Subject: Re: [PATCH v5 01/13] mm: Fix the return type of
 __do_page_cache_readahead
To: Matthew Wilcox <willy@infradead.org>, <linux-fsdevel@vger.kernel.org>
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References: <20200211010348.6872-1-willy@infradead.org>
 <20200211010348.6872-2-willy@infradead.org>
From: John Hubbard <jhubbard@nvidia.com>
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On 2/10/20 5:03 PM, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> 
> ra_submit() which is a wrapper around __do_page_cache_readahead() already
> returns an unsigned long, and the 'nr_to_read' parameter is an unsigned
> long, so fix __do_page_cache_readahead() to return an unsigned long,
> even though I'm pretty sure we're not going to readahead more than 2^32
> pages ever.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>  mm/internal.h  | 2 +-
>  mm/readahead.c | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/internal.h b/mm/internal.h
> index 3cf20ab3ca01..41b93c4b3ab7 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -49,7 +49,7 @@ void unmap_page_range(struct mmu_gather *tlb,
>  			     unsigned long addr, unsigned long end,
>  			     struct zap_details *details);
>  
> -extern unsigned int __do_page_cache_readahead(struct address_space *mapping,
> +extern unsigned long __do_page_cache_readahead(struct address_space *mapping,
>  		struct file *filp, pgoff_t offset, unsigned long nr_to_read,
>  		unsigned long lookahead_size);
>  
> diff --git a/mm/readahead.c b/mm/readahead.c
> index 2fe72cd29b47..6bf73ef33b7e 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -152,7 +152,7 @@ static int read_pages(struct address_space *mapping, struct file *filp,
>   *
>   * Returns the number of pages requested, or the maximum amount of I/O allowed.
>   */
> -unsigned int __do_page_cache_readahead(struct address_space *mapping,
> +unsigned long __do_page_cache_readahead(struct address_space *mapping,
>  		struct file *filp, pgoff_t offset, unsigned long nr_to_read,
>  		unsigned long lookahead_size)
>  {
> @@ -161,7 +161,7 @@ unsigned int __do_page_cache_readahead(struct address_space *mapping,
>  	unsigned long end_index;	/* The last page we want to read */
>  	LIST_HEAD(page_pool);
>  	int page_idx;


What about page_idx, too? It should also have the same data type as nr_pages, as long as
we're trying to be consistent on this point.

Just want to ensure we're ready to handle those 2^33+ page readaheads... :)


thanks,
-- 
John Hubbard
NVIDIA
> -	unsigned int nr_pages = 0;
> +	unsigned long nr_pages = 0;
>  	loff_t isize = i_size_read(inode);
>  	gfp_t gfp_mask = readahead_gfp_mask(mapping);
>  
>