Re: [PATCH v3] mkfs: Break block discard into chunks of 2 GB

[Eric Sandeen <sandeen@sandeen.net>]

On 11/28/19 12:21 AM, Pavel Reichl wrote:
> Some users are not happy about the BLKDISCARD taking too long and at the same
> time not being informed about that - so they think that the command actually
> hung.
> 
> This commit changes code so that progress reporting is possible and also typing
> the ^C will cancel the ongoing BLKDISCARD.

Ok I'm going to nitpick this just a little bit more...

> Signed-off-by: Pavel Reichl <preichl@redhat.com>
> ---
>  mkfs/xfs_mkfs.c | 50 ++++++++++++++++++++++++++++++++++++-------------
>  1 file changed, 37 insertions(+), 13 deletions(-)
> 
> diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
> index 18338a61..0defadb2 100644
> --- a/mkfs/xfs_mkfs.c
> +++ b/mkfs/xfs_mkfs.c
> @@ -1240,17 +1240,40 @@ done:
>  }
>  
>  static void
> -discard_blocks(dev_t dev, uint64_t nsectors)
> +discard_blocks(dev_t dev, uint64_t nsectors, int quiet)
>  {
> -	int fd;
> +	int		fd;
> +	uint64_t	offset = 0;
> +	/* Discard the device 2G at a time */
> +	const uint64_t	step = 2ULL << 30;
> +	const uint64_t	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;
> +	if (!quiet) {
> +		printf("Discarding blocks...\n");
> +		printf("...\n");
> +	}

Let's change this output so that it prints only a single line, i.e.

+	if (!quiet) {
+		printf("Discarding blocks... ");

...

+	if (!quiet)
+		printf("Done.\n");

Then in xfstests there's only one line to filter.

I think there was a suggestion to test isatty() to see if we're on a terminal,
but I have some concern that a hung script will lead to confusion as well if
there's no status message.  We can add terminal testing in a later patch if that
really seems like the right way to go.

If you're ok with the above, I can make the change on commit to save another
patch round trip, and

Reviewed-by: Eric Sandeen <sandeen@redhat.com>

> +
> +	/* The block discarding happens in smaller batches so it can be
> +	 * interrupted prematurely
> +	 */
> +	while (offset < count) {
> +		uint64_t	tmp_step = min(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;
> +	}
> +	if (!quiet)
> +		printf("Done.\n");
>  }
>  
>  static __attribute__((noreturn)) void
> @@ -2507,18 +2530,19 @@ open_devices(
>  
>  static void
>  discard_devices(
> -	struct libxfs_xinit	*xi)
> +	struct libxfs_xinit	*xi,
> +	int			quiet)
>  {
>  	/*
>  	 * This function has to be called after libxfs has been initialized.
>  	 */
>  
>  	if (!xi->disfile)
> -		discard_blocks(xi->ddev, xi->dsize);
> +		discard_blocks(xi->ddev, xi->dsize, quiet);
>  	if (xi->rtdev && !xi->risfile)
> -		discard_blocks(xi->rtdev, xi->rtsize);
> +		discard_blocks(xi->rtdev, xi->rtsize, quiet);
>  	if (xi->logdev && xi->logdev != xi->ddev && !xi->lisfile)
> -		discard_blocks(xi->logdev, xi->logBBsize);
> +		discard_blocks(xi->logdev, xi->logBBsize, quiet);
>  }
>  
>  static void
> @@ -3749,7 +3773,7 @@ main(
>  	 * All values have been validated, discard the old device layout.
>  	 */
>  	if (discard && !dry_run)
> -		discard_devices(&xi);
> +		discard_devices(&xi, quiet);
>  
>  	/*
>  	 * we need the libxfs buffer cache from here on in.
>