Re: [PATCH 1/2] mkfs: Break block discard into chunks of 2 GB

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Thu, Nov 21, 2019 at 10:44:44PM +0100, Pavel Reichl wrote:
> Signed-off-by: Pavel Reichl <preichl@redhat.com>
> ---
>  mkfs/xfs_mkfs.c | 32 +++++++++++++++++++++++++-------
>  1 file changed, 25 insertions(+), 7 deletions(-)
> 
> diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
> index 18338a61..a02d6f66 100644
> --- a/mkfs/xfs_mkfs.c
> +++ b/mkfs/xfs_mkfs.c
> @@ -1242,15 +1242,33 @@ done:
>  static void
>  discard_blocks(dev_t dev, uint64_t nsectors)
>  {
> -	int fd;
> +	int		fd;
> +	uint64_t	offset		= 0;
> +	/* Maximal chunk of bytes to discard is 2GB */
> +	const uint64_t	step		= (uint64_t)2<<30;

You don't need the tabs after the variable name, e.g.

	/* Maximal chunk of bytes to discard is 2GB */
	const uint64_t	step = 2ULL << 30;

> +	/* Sector size is 512 bytes */
> +	const uint64_t	count		= nsectors << 9;

count = BBTOB(nsectors)?

>  
> -	/*
> -	 * We intentionally ignore errors from the discard ioctl.  It is
> -	 * not necessary for the mkfs functionality but just an optimization.
> -	 */
>  	fd = libxfs_device_to_fd(dev);
> -	if (fd > 0)
> -		platform_discard_blocks(fd, 0, nsectors << 9);
> +	if (fd <= 0)
> +		return;
> +
> +	while (offset < count) {
> +		uint64_t	tmp_step = step;

tmp_step = min(step, count - offset); ?

Otherwise seems reasonable to me, if nothing else to avoid the problem
where you ask mkfs to discard and can't cancel it....

--D

> +
> +		if ((offset + step) > count)
> +			tmp_step = count - offset;
> +
> +		/*
> +		 * We intentionally ignore errors from the discard ioctl. It is
> +		 * not necessary for the mkfs functionality but just an
> +		 * optimization. However we should stop on error.
> +		 */
> +		if (platform_discard_blocks(fd, offset, tmp_step))
> +			return;
> +
> +		offset += tmp_step;
> +	}
>  }
>  
>  static __attribute__((noreturn)) void
> -- 
> 2.23.0
>