[RF[CRAP] 2/2] xfs: stop using set_blocksize

Commit Message

Darrick J. Wong April 15, 2025, 12:33 a.m. UTC

From: Darrick J. Wong <[e-mail]>

XFS has its own buffer cache for metadata that uses submit_bio, which
means that it no longer uses the block device pagecache for anything.
Create a more lightweight helper that runs the blocksize checks and
flushes dirty data and use that instead.  No more truncating the
pagecache because why would XFS care? ;)

Signed-off-by: "Darrick J. Wong" <[e-mail]>
---
 include/linux/blkdev.h |    1 +
 block/bdev.c           |   23 +++++++++++++++++++++++
 fs/xfs/xfs_buf.c       |    9 ++++++---
 3 files changed, 30 insertions(+), 3 deletions(-)

Comments

Christoph Hellwig April 16, 2025, 4:46 a.m. UTC | #1

On Mon, Apr 14, 2025 at 05:33:08PM -0700, Darrick J. Wong wrote:
> +/*
> + * For bdev filesystems that do not use buffer heads, check that this block
> + * size is acceptable and flush dirty pagecache to disk.
> + */

Can you turn this into a full fledged kerneldoc comment?

> +int bdev_use_blocksize(struct file *file, int size)
> +{
> +	struct inode *inode = file->f_mapping->host;
> +	struct block_device *bdev = I_BDEV(inode);
> +
> +	if (blk_validate_block_size(size))
> +		return -EINVAL;
> +
> +	/* Size cannot be smaller than the size supported by the device */
> +	if (size < bdev_logical_block_size(bdev))
> +		return -EINVAL;
> +
> +	if (!file->private_data)
> +		return -EINVAL;

This private_data check looks really confusing.  Looking it up I see
that it is directly copied from set_blocksize, but it could really
use a comment.  Or in fact be removed here and kept in set_blocksize
only as we don't care about an exclusive opener at all.   Even there
a comment would be rather helpful, though.

> +
> +	return sync_blockdev(bdev);
> +}

I don't think we need sync_blockdev here as we don't touch the
bdev page cache.  Maybe XFS wants to still call it, but it feels
wrong in a helper just validating the block size.

So maybe drop it, rename the helper to bdev_validate_block_size
and use it in set_blocksize instead of duplicating the logic?

> +	error = bdev_use_blocksize(btp->bt_bdev_file, sectorsize);

.. and then split using it in XFS into a separate patch from adding
the block layer helper.

Darrick J. Wong April 16, 2025, 5:06 a.m. UTC | #2

On Tue, Apr 15, 2025 at 09:46:09PM -0700, Christoph Hellwig wrote:
> On Mon, Apr 14, 2025 at 05:33:08PM -0700, Darrick J. Wong wrote:
> > +/*
> > + * For bdev filesystems that do not use buffer heads, check that this block
> > + * size is acceptable and flush dirty pagecache to disk.
> > + */
> 
> Can you turn this into a full fledged kerneldoc comment?

Ok.

> > +int bdev_use_blocksize(struct file *file, int size)
> > +{
> > +	struct inode *inode = file->f_mapping->host;
> > +	struct block_device *bdev = I_BDEV(inode);
> > +
> > +	if (blk_validate_block_size(size))
> > +		return -EINVAL;
> > +
> > +	/* Size cannot be smaller than the size supported by the device */
> > +	if (size < bdev_logical_block_size(bdev))
> > +		return -EINVAL;
> > +
> > +	if (!file->private_data)
> > +		return -EINVAL;
> 
> This private_data check looks really confusing.  Looking it up I see
> that it is directly copied from set_blocksize, but it could really
> use a comment.  Or in fact be removed here and kept in set_blocksize
> only as we don't care about an exclusive opener at all.   Even there
> a comment would be rather helpful, though.

When even is it null?  I thought it would either be the holder or
bdev_inode if not.

> > +
> > +	return sync_blockdev(bdev);
> > +}
> 
> I don't think we need sync_blockdev here as we don't touch the
> bdev page cache.  Maybe XFS wants to still call it, but it feels
> wrong in a helper just validating the block size.
> 
> So maybe drop it, rename the helper to bdev_validate_block_size
> and use it in set_blocksize instead of duplicating the logic?

Ok.  bdev_validate_block_size is a much better name for a tighter
function...

> > +	error = bdev_use_blocksize(btp->bt_bdev_file, sectorsize);
> 
> .. and then split using it in XFS into a separate patch from adding
> the block layer helper.

...and xfs can call sync_blockdev directly from xfs_setsize_buftarg.
I imagine we still want any dirty pagecache to get flushed before we
start submitting our own read bios.

--D

Patch

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index f442639dfae224..ae83dd12351c2e 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1618,6 +1618,7 @@  static inline void bio_end_io_acct(struct bio *bio, unsigned long start_time)
 	return bio_end_io_acct_remapped(bio, start_time, bio->bi_bdev);
 }
 
+int bdev_use_blocksize(struct file *file, int size);
 int set_blocksize(struct file *file, int size);
 
 int lookup_bdev(const char *pathname, dev_t *dev);
diff --git a/block/bdev.c b/block/bdev.c
index 0cbdac46d98d86..201d61d743592e 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -152,6 +152,29 @@  static void set_init_blocksize(struct block_device *bdev)
 				    get_order(bsize), get_order(bsize));
 }
 
+/*
+ * For bdev filesystems that do not use buffer heads, check that this block
+ * size is acceptable and flush dirty pagecache to disk.
+ */
+int bdev_use_blocksize(struct file *file, int size)
+{
+	struct inode *inode = file->f_mapping->host;
+	struct block_device *bdev = I_BDEV(inode);
+
+	if (blk_validate_block_size(size))
+		return -EINVAL;
+
+	/* Size cannot be smaller than the size supported by the device */
+	if (size < bdev_logical_block_size(bdev))
+		return -EINVAL;
+
+	if (!file->private_data)
+		return -EINVAL;
+
+	return sync_blockdev(bdev);
+}
+EXPORT_SYMBOL_GPL(bdev_use_blocksize);
+
 int set_blocksize(struct file *file, int size)
 {
 	struct inode *inode = file->f_mapping->host;
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 8e7f1b324b3bea..2c8531103c01bb 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -1718,14 +1718,17 @@  xfs_setsize_buftarg(
 	struct xfs_buftarg	*btp,
 	unsigned int		sectorsize)
 {
+	int			error;
+
 	/* Set up metadata sector size info */
 	btp->bt_meta_sectorsize = sectorsize;
 	btp->bt_meta_sectormask = sectorsize - 1;
 
-	if (set_blocksize(btp->bt_bdev_file, sectorsize)) {
+	error = bdev_use_blocksize(btp->bt_bdev_file, sectorsize);
+	if (error) {
 		xfs_warn(btp->bt_mount,
-			"Cannot set_blocksize to %u on device %pg",
-			sectorsize, btp->bt_bdev);
+			"Cannot use blocksize %u on device %pg, err %d",
+			sectorsize, btp->bt_bdev, error);
 		return -EINVAL;
 	}