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SubjectRe: [PATCH 1/2] xfs: cache dax_device lookup result
On Thu, Aug 24, 2017 at 05:35:48PM -0700, Dan Williams wrote:
> The ->iomap_begin() operation is a hot path, so cache the
> fs_dax_get_by_host() result to avoid the incurring the hash lookup
> overhead.

Just out of curiosity (and sorry if this has already been discussed to
death and I'm merely ignorant) but I was wondering why the daxdev isn't
simply attached to the block_device? Is it not a 1:1 mapping?

--D

>
> Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
> Reported-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
> fs/xfs/xfs_aops.c | 24 ++++++++++++++++++++++++
> fs/xfs/xfs_aops.h | 1 +
> fs/xfs/xfs_buf.h | 1 +
> fs/xfs/xfs_iomap.c | 9 +--------
> 4 files changed, 27 insertions(+), 8 deletions(-)
>
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index 6bf120bb1a17..d16e013e1b8c 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -80,6 +80,30 @@ xfs_find_bdev_for_inode(
> return mp->m_ddev_targp->bt_bdev;
> }
>
> +struct dax_device *
> +xfs_find_daxdev_for_inode(
> + struct inode *inode)
> +{
> + struct xfs_inode *ip = XFS_I(inode);
> + struct xfs_mount *mp = ip->i_mount;
> + struct block_device *bdev;
> + xfs_buftarg_t *bt;
> +
> + if (XFS_IS_REALTIME_INODE(ip))
> + bt = mp->m_rtdev_targp;
> + else
> + bt = mp->m_ddev_targp;
> +
> + bdev = bt->bt_bdev;
> + if (!blk_queue_dax(bdev->bd_queue))
> + return NULL;
> +
> + if (!bt->bt_daxdev)
> + bt->bt_daxdev = fs_dax_get_by_host(bdev->bd_disk->disk_name);
> +
> + return bt->bt_daxdev;
> +}
> +
> /*
> * We're now finished for good with this page. Update the page state via the
> * associated buffer_heads, paying attention to the start and end offsets that
> diff --git a/fs/xfs/xfs_aops.h b/fs/xfs/xfs_aops.h
> index cc174ec6c2fd..88c85ea63da0 100644
> --- a/fs/xfs/xfs_aops.h
> +++ b/fs/xfs/xfs_aops.h
> @@ -59,5 +59,6 @@ int xfs_setfilesize(struct xfs_inode *ip, xfs_off_t offset, size_t size);
>
> extern void xfs_count_page_state(struct page *, int *, int *);
> extern struct block_device *xfs_find_bdev_for_inode(struct inode *);
> +extern struct dax_device *xfs_find_daxdev_for_inode(struct inode *);
>
> #endif /* __XFS_AOPS_H__ */
> diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
> index 20721261dae5..fc95a02f272a 100644
> --- a/fs/xfs/xfs_buf.h
> +++ b/fs/xfs/xfs_buf.h
> @@ -108,6 +108,7 @@ typedef unsigned int xfs_buf_flags_t;
> typedef struct xfs_buftarg {
> dev_t bt_dev;
> struct block_device *bt_bdev;
> + struct dax_device *bt_daxdev;
> struct xfs_mount *bt_mount;
> unsigned int bt_meta_sectorsize;
> size_t bt_meta_sectormask;
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index 813394c62849..3e8b9ec9e802 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -69,6 +69,7 @@ xfs_bmbt_to_iomap(
> iomap->offset = XFS_FSB_TO_B(mp, imap->br_startoff);
> iomap->length = XFS_FSB_TO_B(mp, imap->br_blockcount);
> iomap->bdev = xfs_find_bdev_for_inode(VFS_I(ip));
> + iomap->dax_dev = xfs_find_daxdev_for_inode(VFS_I(ip));
> }
>
> xfs_extlen_t
> @@ -976,7 +977,6 @@ xfs_file_iomap_begin(
> int nimaps = 1, error = 0;
> bool shared = false, trimmed = false;
> unsigned lockmode;
> - struct block_device *bdev;
>
> if (XFS_FORCED_SHUTDOWN(mp))
> return -EIO;
> @@ -1087,13 +1087,6 @@ xfs_file_iomap_begin(
>
> xfs_bmbt_to_iomap(ip, iomap, &imap);
>
> - /* optionally associate a dax device with the iomap bdev */
> - bdev = iomap->bdev;
> - if (blk_queue_dax(bdev->bd_queue))
> - iomap->dax_dev = fs_dax_get_by_host(bdev->bd_disk->disk_name);
> - else
> - iomap->dax_dev = NULL;
> -
> if (shared)
> iomap->flags |= IOMAP_F_SHARED;
> return 0;
>

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