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

Pavel Reichl
2019-11-22T14:46:55Z

Thanks Darrick for the comments. It makes sense to me, the next
iteration of the patchset will address that.

On Thu, Nov 21, 2019 at 10:57 PM Darrick J. Wong
<darrick.wong@oracle.com> wrote:
>
> 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
> >
>