Re: [PATCH 5/5] block: truncate page cache only when necessary on fallocate

[Christoph Hellwig <hch@infradead.org>]

why?

On Thu, Apr 06, 2017 at 04:02:49PM +0400, Dmitry Monakhov wrote:
> Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
> ---
>  fs/block_dev.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 2eca00e..f4b13e1 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -2075,7 +2075,7 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
>  {
>  	struct block_device *bdev = I_BDEV(bdev_file_inode(file));
>  	struct request_queue *q = bdev_get_queue(bdev);
> -	struct address_space *mapping;
> +	struct address_space *mapping = bdev->bd_inode->i_mapping;
>  	loff_t end = start + len - 1;
>  	loff_t isize;
>  	int error;
> @@ -2102,13 +2102,10 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
>  	if ((start | len) & (bdev_logical_block_size(bdev) - 1))
>  		return -EINVAL;
>  
> -	/* Invalidate the page cache, including dirty pages. */
> -	mapping = bdev->bd_inode->i_mapping;
> -	truncate_inode_pages_range(mapping, start, end);
> -
>  	switch (mode) {
>  	case FALLOC_FL_ZERO_RANGE:
>  	case FALLOC_FL_ZERO_RANGE | FALLOC_FL_KEEP_SIZE:
> +		truncate_inode_pages_range(mapping, start, end);
>  		error = blkdev_issue_zeroout(bdev, start >> 9, len >> 9,
>  					    GFP_KERNEL, false);
>  		break;
> @@ -2116,12 +2113,14 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
>  		/* Only punch if the device can do zeroing discard. */
>  		if (!blk_queue_discard(q) || !q->limits.discard_zeroes_data)
>  			return -EOPNOTSUPP;
> +		truncate_inode_pages_range(mapping, start, end);
>  		error = blkdev_issue_discard(bdev, start >> 9, len >> 9,
>  					     GFP_KERNEL, 0);
>  		break;
>  	case FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE | FALLOC_FL_NO_HIDE_STALE:
>  		if (!blk_queue_discard(q))
>  			return -EOPNOTSUPP;
> +		truncate_inode_pages_range(mapping, start, end);
>  		error = blkdev_issue_discard(bdev, start >> 9, len >> 9,
>  					     GFP_KERNEL, 0);
>  		break;
> -- 
> 2.9.3
> 
---end quoted text---