Re: [RFC PATCH] block: wire blkdev_fallocate() to block_device_operations' reserve_space

Darrick J. Wong
2016-04-12T22:25:34Z

On Tue, Apr 12, 2016 at 04:46:58PM -0400, Mike Snitzer wrote:
> On Tue, Apr 12 2016 at 4:39pm -0400,
> Darrick J. Wong <darrick.wong@oracle.com> wrote:
>
> > On Tue, Apr 12, 2016 at 04:04:59PM -0400, Mike Snitzer wrote:
> > > On Tue, Apr 12 2016 at 12:42P -0400,
> > > Brian Foster <bfoster@redhat.com> wrote:
> > >
> > > > Hi all,
> > > >
> > > > This is v2 of the XFS and block device reservation experiment. The
> > > > significant changes in v2 are that the bdev interface has been condensed
> > > > to a single callback function, the XFS transaction reservation
> > > > management has been reworked to make transactions responsible for
> > > > tracking and releasing excess reservation (for non-delalloc cases) and a
> > > > workaround for the fallocate over-reservation issue is included. Beyond
> > > > that, this version adds a bunch of miscellaneous cleanups and fixes some
> > > > of the nastier locking/leak issues present in the first rfc.
> > > >
> > > > Patches 1-2 refactor some XFS reserve pool and block accounting code in
> > > > preparation for subsequent patches. Patches 3-5 add block/device-mapper
> > > > reservation support. Patches 6-10 add the core reservation
> > > > infrastructure and management bits to XFS. See the link to the original
> > > > rfc below for instructions and further details around the purpose of
> > > > this series.
> > > >
> > > > Finally, note that this is still highly experimental/theoretical and
> > > > should not be used on production systems. Thoughts, reviews, flames
> > > > appreciated.
> > >
> > > Thanks for carrying on with this work Brian.
> > >
> > > I've started to review your patchset and Darrick's fallocate patchset.
> > > I've pushed a branch to linux-dm.git that combines the 2, see:
> > > https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/log/?h=dm-fallocate
> > >
> > > and then added this RFC patch, at the end, which relies on both of your
> > > patchsets -- you'll see blkdev_ensure_space_exists() has a FIXME which
> > > implies it isn't much more than simply stubbed out at this point
> > > (completely untested):
> >
> > Hmm, ok, but -rc3 broke a bunch of stuff. Guess I should repost with all
> > the PAGE_CACHE_ -> PAGE_ stuff fixed. :)
>
> Yeah, the kernel.org kbuild robots just spammed us about that same exact
> breakage.
>
> > > From: Mike Snitzer <snitzer@redhat.com>
> > > Date: Tue, 12 Apr 2016 15:54:31 -0400
> > > Subject: [RFC PATCH] block: wire blkdev_fallocate() to block_device_operations' reserve_space
> > >
> > > This effectively exposes the primitive for "ensure space exists". It
> > > relies on block_device_operations' reserve_space method.
> > >
> > > Signed-off-by: Mike Snitzer <snitzer@redhat.com>
> > > ---
> > > block/blk-lib.c | 26 ++++++++++++++++++++++++++
> > > fs/block_dev.c | 20 +++++++++++---------
> > > include/linux/blkdev.h | 2 ++
> > > 3 files changed, 39 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/block/blk-lib.c b/block/blk-lib.c
> > > index 9dca6bb..5042a84 100644
> > > --- a/block/blk-lib.c
> > > +++ b/block/blk-lib.c
> > > @@ -314,3 +314,29 @@ int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
> > > return __blkdev_issue_zeroout(bdev, sector, nr_sects, gfp_mask);
> > > }
> > > EXPORT_SYMBOL(blkdev_issue_zeroout);
> > > +
> > > +/**
> > > + * blkdev_ensure_space_exists - preallocate a block range
> > > + * @bdev: blockdev to preallocate space for
> > > + * @sector: start sector
> > > + * @nr_sects: number of sectors to preallocate
> > > + * @gfp_mask: memory allocation flags (for bio_alloc)
> > > + * @flags: FALLOC_FL_* to control behaviour
> > > + *
> > > + * Description:
> > > + * Ensure space exists, or is preallocated, for the sectors in question.
> > > + */
> > > +int blkdev_ensure_space_exists(struct block_device *bdev, sector_t sector,
> > > + sector_t nr_sects, unsigned long flags)
> > > +{
> > > + sector_t res;
> > > + const struct block_device_operations *ops = bdev->bd_disk->fops;
> > > +
> > > + if (!ops->reserve_space)
> > > + return -EOPNOTSUPP;
> > > +
> > > + // FIXME: check with Brian Foster on whether it makes sense to
> > > + // use BDEV_RES_GET/BDEV_RES_MOD instead of BDEV_RES_PROVISION?
> > > + return ops->reserve_space(bdev, BDEV_RES_PROVISION, sector, nr_sects, &res);
> >
> > /me thinks BDEV_RES_PROVISION is correct here, because regular-mode file
> > fallocate (for ext4/xfs anyway) allocates blocks and maps them to specific file
> > offsets as unwritten extents. afaict RES_PROVISION -> thin_provision_space()
> > and thin_provision_space() seems to allocate blocks and map them to the
> > device's LBAs.
> >
> > If I'm reading the patches correctly, RES_GET/RES_MOD seem to reserve N blocks
> > but doesn't map them to any specific LBA.
>
> Right that is how I read it too. I just put that FIXME in to cover my
> ass incase I was being an idiot ;)

<nod>

> > > +}
> > > +EXPORT_SYMBOL(blkdev_ensure_space_exists);
> > > diff --git a/fs/block_dev.c b/fs/block_dev.c
> > > index 5a2c3ab..b34c07b 100644
> > > --- a/fs/block_dev.c
> > > +++ b/fs/block_dev.c
> > > @@ -1801,17 +1801,13 @@ long blkdev_fallocate(struct file *file, int mode, loff_t start, loff_t len)
> > > struct request_queue *q = bdev_get_queue(bdev);
> > > struct address_space *mapping;
> > > loff_t end = start + len - 1;
> > > - loff_t bs_mask, isize;
> > > + loff_t isize;
> > > int error;
> > >
> > > /* We only support zero range and punch hole. */
> > > if (mode & ~BLKDEV_FALLOC_FL_SUPPORTED)
> > > return -EOPNOTSUPP;
> > >
> > > - /* We haven't a primitive for "ensure space exists" right now. */
> > > - if (!(mode & ~FALLOC_FL_KEEP_SIZE))
> > > - return -EOPNOTSUPP;
> > > -
> > > /* Only punch if the device can do zeroing discard. */
> > > if ((mode & FALLOC_FL_PUNCH_HOLE) &&
> > > (!blk_queue_discard(q) || !q->limits.discard_zeroes_data))
> > > @@ -1829,9 +1825,12 @@ long blkdev_fallocate(struct file *file, int mode, loff_t start, loff_t len)
> > > return -EINVAL;
> > > }
> > >
> > > - /* Don't allow IO that isn't aligned to logical block size */
> > > - bs_mask = bdev_logical_block_size(bdev) - 1;
> > > - if ((start | len) & bs_mask)
> > > + /*
> > > + * Don't allow IO that isn't aligned to minimum IO size (io_min)
> > > + * - for normal device's io_min is usually logical block size
> > > + * - but for more exotic devices (e.g. DM thinp) it may be larger
> > > + */
> > > + if ((start | len) % bdev_io_min(bdev))
> > > return -EINVAL;
> >
> > Noted. Will update the original patch.
>
> OK, thanks.
>
> Once your new patchset is available I'll rebase my 'dm-fallocate' test
> branch accordingly.
>
> > > /* Invalidate the page cache, including dirty pages. */
> > > @@ -1839,7 +1838,10 @@ long blkdev_fallocate(struct file *file, int mode, loff_t start, loff_t len)
> > > truncate_inode_pages_range(mapping, start, end);
> > >
> > > error = -EINVAL;
> > > - if (mode & FALLOC_FL_ZERO_RANGE)
> > > + if (!(mode & ~FALLOC_FL_KEEP_SIZE))
> > > + error = blkdev_ensure_space_exists(bdev, start >> 9, len >> 9,
> > > + mode);
> > > + else if (mode & FALLOC_FL_ZERO_RANGE)
> >
> > This whole thing got converted to a switch statement due to some feedback
> > from hch.
> >
> > Anyway, will try to have a new blockdev fallocate patchset done by the end
> > of the day.
> >
> > (Is there a test case for this?)
>
> No, but once my patch is in place to join your patchset with Brian's
> then any basic fallocate tests against a DM thinp volume _should_ work.
>
> /me assumes xfstests has such tests? Only missing bit would be to layer
> the filesystem ontop of DM thinp? Or extend the tests your added to
> test DM thinp devices directly. I think Eric Sandeen (now cc'd) made
> xfstests capable or creating DM thinp volumes for certain tests.

The patches got reviewed but aren't upstream. It looks like it wouldn't
be difficult once it lands to make a test case that tests fallocate directly
on a thinp device.

--D

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