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

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

On Mon, Dec 09, 2019 at 04:00:17PM -0600, Eric Sandeen wrote:
> 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... ");

This needs fflush(stdout); here to force the message out of stdio output
buffering.

--D

> 
> ...
> 
> +	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.
> >