linux-kernel - Re: [PATCH v6 5/8] fs: xfs: replace BIO_MAX_SECTORS with BIO_MAX

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Date:	Wed, 1 Jun 2016 06:48:16 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Jens Axboe <axboe@...com>, linux-kernel@...r.kernel.org,
	linux-block@...r.kernel.org, Christoph Hellwig <hch@...radead.org>,
	Dave Chinner <david@...morbit.com>,
	"supporter:XFS FILESYSTEM" <xfs@....sgi.com>
Subject: Re: [PATCH v6 5/8] fs: xfs: replace BIO_MAX_SECTORS with
 BIO_MAX_PAGES

On Mon, May 30, 2016 at 09:34:33PM +0800, Ming Lei wrote:
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index e71cfbd..e5d713b 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -1157,9 +1157,7 @@ xfs_buf_ioapply_map(
>  
>  next_chunk:
>  	atomic_inc(&bp->b_io_remaining);
> -	nr_pages = BIO_MAX_SECTORS >> (PAGE_SHIFT - BBSHIFT);
> -	if (nr_pages > total_nr_pages)
> -		nr_pages = total_nr_pages;
> +	nr_pages = min(total_nr_pages, BIO_MAX_PAGES);
>  
>  	bio = bio_alloc(GFP_NOIO, nr_pages);

While I think this is a useful cleanup on it's own I think
you'd make everyones life easier if bio_alloc simply clamped down
the passed nr_pages value to the maximum allowed.