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Date: Fri, 3 Jan 2020 09:12:35 -0500
From: Vivek Goyal <vgoyal@...hat.com>
To: Dan Williams <dan.j.williams@...el.com>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-nvdimm@...ts.01.org, virtio-fs@...hat.com, miklos@...redi.hu,
stefanha@...hat.com, dgilbert@...hat.com,
Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 02/19] dax: Pass dax_dev to dax_writeback_mapping_range()
On Mon, Aug 26, 2019 at 04:58:29PM -0400, Vivek Goyal wrote:
> On Mon, Aug 26, 2019 at 04:33:26PM -0400, Vivek Goyal wrote:
> > On Mon, Aug 26, 2019 at 04:53:16AM -0700, Christoph Hellwig wrote:
> > > On Wed, Aug 21, 2019 at 01:57:03PM -0400, Vivek Goyal wrote:
> > > > Right now dax_writeback_mapping_range() is passed a bdev and dax_dev
> > > > is searched from that bdev name.
> > > >
> > > > virtio-fs does not have a bdev. So pass in dax_dev also to
> > > > dax_writeback_mapping_range(). If dax_dev is passed in, bdev is not
> > > > used otherwise dax_dev is searched using bdev.
> > >
> > > Please just pass in only the dax_device and get rid of the block device.
> > > The callers should have one at hand easily, e.g. for XFS just call
> > > xfs_find_daxdev_for_inode instead of xfs_find_bdev_for_inode.
> >
> > Sure. Here is the updated patch.
> >
> > This patch can probably go upstream independently. If you are fine with
> > the patch, I can post it separately for inclusion.
>
> Forgot to update function declaration in case of !CONFIG_FS_DAX. Here is
> the updated patch.
>
> Subject: dax: Pass dax_dev instead of bdev to dax_writeback_mapping_range()
>
> As of now dax_writeback_mapping_range() takes "struct block_device" as a
> parameter and dax_dev is searched from bdev name. This also involves taking
> a fresh reference on dax_dev and putting that reference at the end of
> function.
>
> We are developing a new filesystem virtio-fs and using dax to access host
> page cache directly. But there is no block device. IOW, we want to make
> use of dax but want to get rid of this assumption that there is always
> a block device associated with dax_dev.
>
> So pass in "struct dax_device" as parameter instead of bdev.
>
> ext2/ext4/xfs are current users and they already have a reference on
> dax_device. So there is no need to take reference and drop reference to
> dax_device on each call of this function.
>
> Suggested-by: Christoph Hellwig <hch@...radead.org>
> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>
Hi Dan,
Ping for this patch. I see christoph and Jan acked it. Can we take it. Not
sure how to get ack from ext4 developers.
Thanks
Vivek
> ---
> fs/dax.c | 8 +-------
> fs/ext2/inode.c | 5 +++--
> fs/ext4/inode.c | 2 +-
> fs/xfs/xfs_aops.c | 2 +-
> include/linux/dax.h | 4 ++--
> 5 files changed, 8 insertions(+), 13 deletions(-)
>
> Index: rhvgoyal-linux-fuse/fs/dax.c
> ===================================================================
> --- rhvgoyal-linux-fuse.orig/fs/dax.c 2019-08-26 16:45:26.093710196 -0400
> +++ rhvgoyal-linux-fuse/fs/dax.c 2019-08-26 16:45:29.462710196 -0400
> @@ -936,12 +936,11 @@ static int dax_writeback_one(struct xa_s
> * on persistent storage prior to completion of the operation.
> */
> int dax_writeback_mapping_range(struct address_space *mapping,
> - struct block_device *bdev, struct writeback_control *wbc)
> + struct dax_device *dax_dev, struct writeback_control *wbc)
> {
> XA_STATE(xas, &mapping->i_pages, wbc->range_start >> PAGE_SHIFT);
> struct inode *inode = mapping->host;
> pgoff_t end_index = wbc->range_end >> PAGE_SHIFT;
> - struct dax_device *dax_dev;
> void *entry;
> int ret = 0;
> unsigned int scanned = 0;
> @@ -952,10 +951,6 @@ int dax_writeback_mapping_range(struct a
> if (!mapping->nrexceptional || wbc->sync_mode != WB_SYNC_ALL)
> return 0;
>
> - dax_dev = dax_get_by_host(bdev->bd_disk->disk_name);
> - if (!dax_dev)
> - return -EIO;
> -
> trace_dax_writeback_range(inode, xas.xa_index, end_index);
>
> tag_pages_for_writeback(mapping, xas.xa_index, end_index);
> @@ -976,7 +971,6 @@ int dax_writeback_mapping_range(struct a
> xas_lock_irq(&xas);
> }
> xas_unlock_irq(&xas);
> - put_dax(dax_dev);
> trace_dax_writeback_range_done(inode, xas.xa_index, end_index);
> return ret;
> }
> Index: rhvgoyal-linux-fuse/include/linux/dax.h
> ===================================================================
> --- rhvgoyal-linux-fuse.orig/include/linux/dax.h 2019-08-26 16:45:26.094710196 -0400
> +++ rhvgoyal-linux-fuse/include/linux/dax.h 2019-08-26 16:46:08.101710196 -0400
> @@ -141,7 +141,7 @@ static inline void fs_put_dax(struct dax
>
> struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev);
> int dax_writeback_mapping_range(struct address_space *mapping,
> - struct block_device *bdev, struct writeback_control *wbc);
> + struct dax_device *dax_dev, struct writeback_control *wbc);
>
> struct page *dax_layout_busy_page(struct address_space *mapping);
> dax_entry_t dax_lock_page(struct page *page);
> @@ -180,7 +180,7 @@ static inline struct page *dax_layout_bu
> }
>
> static inline int dax_writeback_mapping_range(struct address_space *mapping,
> - struct block_device *bdev, struct writeback_control *wbc)
> + struct dax_device *dax_dev, struct writeback_control *wbc)
> {
> return -EOPNOTSUPP;
> }
> Index: rhvgoyal-linux-fuse/fs/xfs/xfs_aops.c
> ===================================================================
> --- rhvgoyal-linux-fuse.orig/fs/xfs/xfs_aops.c 2019-08-26 16:45:26.094710196 -0400
> +++ rhvgoyal-linux-fuse/fs/xfs/xfs_aops.c 2019-08-26 16:45:29.471710196 -0400
> @@ -1120,7 +1120,7 @@ xfs_dax_writepages(
> {
> xfs_iflags_clear(XFS_I(mapping->host), XFS_ITRUNCATED);
> return dax_writeback_mapping_range(mapping,
> - xfs_find_bdev_for_inode(mapping->host), wbc);
> + xfs_find_daxdev_for_inode(mapping->host), wbc);
> }
>
> STATIC int
> Index: rhvgoyal-linux-fuse/fs/ext4/inode.c
> ===================================================================
> --- rhvgoyal-linux-fuse.orig/fs/ext4/inode.c 2019-08-26 16:45:26.093710196 -0400
> +++ rhvgoyal-linux-fuse/fs/ext4/inode.c 2019-08-26 16:45:29.475710196 -0400
> @@ -2992,7 +2992,7 @@ static int ext4_dax_writepages(struct ad
> percpu_down_read(&sbi->s_journal_flag_rwsem);
> trace_ext4_writepages(inode, wbc);
>
> - ret = dax_writeback_mapping_range(mapping, inode->i_sb->s_bdev, wbc);
> + ret = dax_writeback_mapping_range(mapping, sbi->s_daxdev, wbc);
> trace_ext4_writepages_result(inode, wbc, ret,
> nr_to_write - wbc->nr_to_write);
> percpu_up_read(&sbi->s_journal_flag_rwsem);
> Index: rhvgoyal-linux-fuse/fs/ext2/inode.c
> ===================================================================
> --- rhvgoyal-linux-fuse.orig/fs/ext2/inode.c 2019-08-26 16:45:26.093710196 -0400
> +++ rhvgoyal-linux-fuse/fs/ext2/inode.c 2019-08-26 16:45:29.477710196 -0400
> @@ -957,8 +957,9 @@ ext2_writepages(struct address_space *ma
> static int
> ext2_dax_writepages(struct address_space *mapping, struct writeback_control *wbc)
> {
> - return dax_writeback_mapping_range(mapping,
> - mapping->host->i_sb->s_bdev, wbc);
> + struct ext2_sb_info *sbi = EXT2_SB(mapping->host->i_sb);
> +
> + return dax_writeback_mapping_range(mapping, sbi->s_daxdev, wbc);
> }
>
> const struct address_space_operations ext2_aops = {
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