Re: [PATCH 2/5] buffer: Calculate block number inside folio_init_buffers()

[Pankaj Raghav <p.raghav@samsung.com>]

On Tue, Nov 07, 2023 at 07:41:49PM +0000, Matthew Wilcox (Oracle) wrote:
> The calculation of block from index doesn't work for devices with a block
> size larger than PAGE_SIZE as we end up shifting by a negative number.
> Instead, calculate the number of the first block from the folio's
> position in the block device.  We no longer need to pass sizebits to
> grow_dev_folio().
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Not totally related to the patch but even though the variable "block"
is sector_t type, but it represents the block number in logical block
size unit of the device? My mind directly went to sector_t being 512
bytes blocks.

But the math checks out.
Reviewed-by: Pankaj Raghav <p.raghav@samsung.com>
> ---
>  fs/buffer.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 8dad6c691e14..cd114110b27f 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -995,11 +995,12 @@ static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
>   * Initialise the state of a blockdev folio's buffers.
>   */ 
>  static sector_t folio_init_buffers(struct folio *folio,
> -		struct block_device *bdev, sector_t block, int size)
> +		struct block_device *bdev, int size)
>  {
>  	struct buffer_head *head = folio_buffers(folio);
>  	struct buffer_head *bh = head;
>  	bool uptodate = folio_test_uptodate(folio);
> +	sector_t block = folio_pos(folio) / size;
>  	sector_t end_block = blkdev_max_block(bdev, size);
>  
>  	do {
> @@ -1032,7 +1033,7 @@ static sector_t folio_init_buffers(struct folio *folio,
>   * we succeeded, or the caller should retry.
>   */
>  static bool grow_dev_folio(struct block_device *bdev, sector_t block,
> -		pgoff_t index, unsigned size, int sizebits, gfp_t gfp)
> +		pgoff_t index, unsigned size, gfp_t gfp)
>  {
>  	struct inode *inode = bdev->bd_inode;
>  	struct folio *folio;
> @@ -1047,8 +1048,7 @@ static bool grow_dev_folio(struct block_device *bdev, sector_t block,
>  	bh = folio_buffers(folio);
>  	if (bh) {
>  		if (bh->b_size == size) {
> -			end_block = folio_init_buffers(folio, bdev,
> -					(sector_t)index << sizebits, size);
> +			end_block = folio_init_buffers(folio, bdev, size);
>  			goto unlock;
>  		}
>  
> @@ -1069,8 +1069,7 @@ static bool grow_dev_folio(struct block_device *bdev, sector_t block,
>  	 */
>  	spin_lock(&inode->i_mapping->private_lock);
>  	link_dev_buffers(folio, bh);
> -	end_block = folio_init_buffers(folio, bdev,
> -			(sector_t)index << sizebits, size);
> +	end_block = folio_init_buffers(folio, bdev, size);
>  	spin_unlock(&inode->i_mapping->private_lock);
>  unlock:
>  	folio_unlock(folio);
> @@ -1105,7 +1104,7 @@ static bool grow_buffers(struct block_device *bdev, sector_t block,
>  	}
>  
>  	/* Create a folio with the proper size buffers */
> -	return grow_dev_folio(bdev, block, index, size, sizebits, gfp);
> +	return grow_dev_folio(bdev, block, index, size, gfp);
>  }
>  
>  static struct buffer_head *
> -- 
> 2.42.0
> 

-- 
Pankaj Raghav