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

Darrick J. Wong
2016-04-12T20:39:15Z

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. :)

> 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.

> +}
> +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.

> /* 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?)

--D

> error = blkdev_issue_zeroout(bdev, start >> 9, len >> 9,
> GFP_KERNEL, false);
> else if (mode & FALLOC_FL_PUNCH_HOLE)
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 6c6ea96..4147af2 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1132,6 +1132,8 @@ extern int blkdev_issue_write_same(struct block_device *bdev, sector_t sector,
> sector_t nr_sects, gfp_t gfp_mask, struct page *page);
> extern int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
> sector_t nr_sects, gfp_t gfp_mask, bool discard);
> +extern int blkdev_ensure_space_exists(struct block_device *bdev, sector_t sector,
> + sector_t nr_sects, unsigned long flags);
> static inline int sb_issue_discard(struct super_block *sb, sector_t block,
> sector_t nr_blocks, gfp_t gfp_mask, unsigned long flags)
> {
> --
> 2.6.4 (Apple Git-63)
>
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