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Subject: Re: [PATCH v7 04/24] mm: Move readahead nr_pages check into
 read_pages
To:     Matthew Wilcox <willy@infradead.org>,
        <linux-fsdevel@vger.kernel.org>
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References: <20200219210103.32400-1-willy@infradead.org>
 <20200219210103.32400-5-willy@infradead.org>
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From:   John Hubbard <jhubbard@nvidia.com>
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On 2/19/20 1:00 PM, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> 
> Simplify the callers by moving the check for nr_pages and the BUG_ON
> into read_pages().
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>  mm/readahead.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 

Looks nice,

    Reviewed-by: John Hubbard <jhubbard@nvidia.com>


thanks,
-- 
John Hubbard
NVIDIA

> diff --git a/mm/readahead.c b/mm/readahead.c
> index 61b15b6b9e72..9fcd4e32b62d 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -119,6 +119,9 @@ static void read_pages(struct address_space *mapping, struct file *filp,
>  	struct blk_plug plug;
>  	unsigned page_idx;
>  
> +	if (!nr_pages)
> +		return;
> +
>  	blk_start_plug(&plug);
>  
>  	if (mapping->a_ops->readpages) {
> @@ -138,6 +141,8 @@ static void read_pages(struct address_space *mapping, struct file *filp,
>  
>  out:
>  	blk_finish_plug(&plug);
> +
> +	BUG_ON(!list_empty(pages));
>  }
>  
>  /*
> @@ -180,8 +185,7 @@ void __do_page_cache_readahead(struct address_space *mapping,
>  			 * contiguous pages before continuing with the next
>  			 * batch.
>  			 */
> -			if (nr_pages)
> -				read_pages(mapping, filp, &page_pool, nr_pages,
> +			read_pages(mapping, filp, &page_pool, nr_pages,
>  						gfp_mask);
>  			nr_pages = 0;
>  			continue;
> @@ -202,9 +206,7 @@ void __do_page_cache_readahead(struct address_space *mapping,
>  	 * uptodate then the caller will launch readpage again, and
>  	 * will then handle the error.
>  	 */
> -	if (nr_pages)
> -		read_pages(mapping, filp, &page_pool, nr_pages, gfp_mask);
> -	BUG_ON(!list_empty(&page_pool));
> +	read_pages(mapping, filp, &page_pool, nr_pages, gfp_mask);
>  }
>  
>  /*
>