linux-kernel - Re: [PATCH v7 04/24] mm: Move readahead nr_pages check into read

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Date:   Thu, 20 Feb 2020 20:24:52 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Matthew Wilcox <willy@...radead.org>,
        <linux-fsdevel@...r.kernel.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <linux-btrfs@...r.kernel.org>, <linux-erofs@...ts.ozlabs.org>,
        <linux-ext4@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>,
        <cluster-devel@...hat.com>, <ocfs2-devel@....oracle.com>,
        <linux-xfs@...r.kernel.org>
Subject: Re: [PATCH v7 04/24] mm: Move readahead nr_pages check into
 read_pages

On 2/19/20 1:00 PM, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@...radead.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@...radead.org>
> ---
>  mm/readahead.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 

Looks nice,

    Reviewed-by: John Hubbard <jhubbard@...dia.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);
>  }
>  
>  /*
>