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Date:   Sun, 27 Aug 2017 20:48:40 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     linux-fsdevel@...r.kernel.org
Cc:     jack@...e.cz, linux-nvdimm@...ts.01.org,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        linux-xfs@...r.kernel.org, linux-ext4@...r.kernel.org, hch@....de
Subject: [PATCH v2 1/2] fs, xfs: perform dax_device lookup at mount

The ->iomap_begin() operation is a hot path, so cache the
fs_dax_get_by_host() result at mount time to avoid the incurring the
hash lookup overhead on a per-i/o basis.

Cc: "Darrick J. Wong" <darrick.wong@...cle.com>
Reported-by: Christoph Hellwig <hch@....de>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 drivers/dax/super.c |   10 ++++++++++
 fs/super.c          |   26 +++++++++++++++++++++++---
 fs/xfs/xfs_aops.c   |   13 +++++++++++++
 fs/xfs/xfs_aops.h   |    1 +
 fs/xfs/xfs_buf.c    |    4 +++-
 fs/xfs/xfs_buf.h    |    3 ++-
 fs/xfs/xfs_iomap.c  |   10 +---------
 fs/xfs/xfs_super.c  |   21 +++++++++++++++++----
 include/linux/dax.h |    6 ++++++
 include/linux/fs.h  |    1 +
 10 files changed, 77 insertions(+), 18 deletions(-)

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 938eb4868f7f..b699aac268a6 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -46,6 +46,8 @@ void dax_read_unlock(int id)
 EXPORT_SYMBOL_GPL(dax_read_unlock);
 
 #ifdef CONFIG_BLOCK
+#include <linux/blkdev.h>
+
 int bdev_dax_pgoff(struct block_device *bdev, sector_t sector, size_t size,
 		pgoff_t *pgoff)
 {
@@ -59,6 +61,14 @@ int bdev_dax_pgoff(struct block_device *bdev, sector_t sector, size_t size,
 }
 EXPORT_SYMBOL(bdev_dax_pgoff);
 
+struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
+{
+	if (!blk_queue_dax(bdev->bd_queue))
+		return NULL;
+	return fs_dax_get_by_host(bdev->bd_disk->disk_name);
+}
+EXPORT_SYMBOL_GPL(fs_dax_get_by_bdev);
+
 /**
  * __bdev_dax_supported() - Check if the device supports dax for filesystem
  * @sb: The superblock of the device
diff --git a/fs/super.c b/fs/super.c
index 6bc3352adcf3..671889b02bed 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -23,6 +23,7 @@
 #include <linux/export.h>
 #include <linux/slab.h>
 #include <linux/blkdev.h>
+#include <linux/dax.h>
 #include <linux/mount.h>
 #include <linux/security.h>
 #include <linux/writeback.h>		/* for the emergency remount stuff */
@@ -1048,9 +1049,17 @@ struct dentry *mount_ns(struct file_system_type *fs_type,
 EXPORT_SYMBOL(mount_ns);
 
 #ifdef CONFIG_BLOCK
+struct sget_devs {
+	struct block_device *bdev;
+	struct dax_device *dax_dev;
+};
+
 static int set_bdev_super(struct super_block *s, void *data)
 {
-	s->s_bdev = data;
+	struct sget_devs *devs = data;
+
+	s->s_bdev = devs->bdev;
+	s->s_daxdev = devs->dax_dev;
 	s->s_dev = s->s_bdev->bd_dev;
 	s->s_bdi = bdi_get(s->s_bdev->bd_bdi);
 
@@ -1059,14 +1068,18 @@ static int set_bdev_super(struct super_block *s, void *data)
 
 static int test_bdev_super(struct super_block *s, void *data)
 {
-	return (void *)s->s_bdev == data;
+	struct sget_devs *devs = data;
+
+	return s->s_bdev == devs->bdev;
 }
 
 struct dentry *mount_bdev(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *data,
 	int (*fill_super)(struct super_block *, void *, int))
 {
+	struct sget_devs devs;
 	struct block_device *bdev;
+	struct dax_device *dax_dev;
 	struct super_block *s;
 	fmode_t mode = FMODE_READ | FMODE_EXCL;
 	int error = 0;
@@ -1077,6 +1090,7 @@ struct dentry *mount_bdev(struct file_system_type *fs_type,
 	bdev = blkdev_get_by_path(dev_name, mode, fs_type);
 	if (IS_ERR(bdev))
 		return ERR_CAST(bdev);
+	dax_dev = fs_dax_get_by_bdev(bdev);
 
 	/*
 	 * once the super is inserted into the list by sget, s_umount
@@ -1089,8 +1103,10 @@ struct dentry *mount_bdev(struct file_system_type *fs_type,
 		error = -EBUSY;
 		goto error_bdev;
 	}
+	devs.bdev = bdev;
+	devs.dax_dev = dax_dev;
 	s = sget(fs_type, test_bdev_super, set_bdev_super, flags | MS_NOSEC,
-		 bdev);
+		 &devs);
 	mutex_unlock(&bdev->bd_fsfreeze_mutex);
 	if (IS_ERR(s))
 		goto error_s;
@@ -1111,6 +1127,7 @@ struct dentry *mount_bdev(struct file_system_type *fs_type,
 		 */
 		up_write(&s->s_umount);
 		blkdev_put(bdev, mode);
+		fs_put_dax(dax_dev);
 		down_write(&s->s_umount);
 	} else {
 		s->s_mode = mode;
@@ -1132,6 +1149,7 @@ struct dentry *mount_bdev(struct file_system_type *fs_type,
 	error = PTR_ERR(s);
 error_bdev:
 	blkdev_put(bdev, mode);
+	fs_put_dax(dax_dev);
 error:
 	return ERR_PTR(error);
 }
@@ -1140,6 +1158,7 @@ EXPORT_SYMBOL(mount_bdev);
 void kill_block_super(struct super_block *sb)
 {
 	struct block_device *bdev = sb->s_bdev;
+	struct dax_device *dax_dev = sb->s_daxdev;
 	fmode_t mode = sb->s_mode;
 
 	bdev->bd_super = NULL;
@@ -1147,6 +1166,7 @@ void kill_block_super(struct super_block *sb)
 	sync_blockdev(bdev);
 	WARN_ON_ONCE(!(mode & FMODE_EXCL));
 	blkdev_put(bdev, mode | FMODE_EXCL);
+	fs_put_dax(dax_dev);
 }
 
 EXPORT_SYMBOL(kill_block_super);
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 6bf120bb1a17..78185f3b10b2 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -80,6 +80,19 @@ 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;
+
+	if (XFS_IS_REALTIME_INODE(ip))
+		return mp->m_rtdev_targp->bt_daxdev;
+	else
+		return mp->m_ddev_targp->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.c b/fs/xfs/xfs_buf.c
index 72f038492ba8..6deb86c845d1 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -1802,7 +1802,8 @@ xfs_setsize_buftarg_early(
 xfs_buftarg_t *
 xfs_alloc_buftarg(
 	struct xfs_mount	*mp,
-	struct block_device	*bdev)
+	struct block_device	*bdev,
+	struct dax_device	*dax_dev)
 {
 	xfs_buftarg_t		*btp;
 
@@ -1811,6 +1812,7 @@ xfs_alloc_buftarg(
 	btp->bt_mount = mp;
 	btp->bt_dev =  bdev->bd_dev;
 	btp->bt_bdev = bdev;
+	btp->bt_daxdev = dax_dev;
 
 	if (xfs_setsize_buftarg_early(btp, bdev))
 		goto error;
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index 20721261dae5..bf71507ddb16 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;
@@ -385,7 +386,7 @@ xfs_buf_update_cksum(struct xfs_buf *bp, unsigned long cksum_offset)
  *	Handling of buftargs.
  */
 extern xfs_buftarg_t *xfs_alloc_buftarg(struct xfs_mount *,
-			struct block_device *);
+			struct block_device *, struct dax_device *);
 extern void xfs_free_buftarg(struct xfs_mount *, struct xfs_buftarg *);
 extern void xfs_wait_buftarg(xfs_buftarg_t *);
 extern int xfs_setsize_buftarg(xfs_buftarg_t *, unsigned int);
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 813394c62849..7c934e407332 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;
@@ -1171,7 +1164,6 @@ xfs_file_iomap_end(
 	unsigned		flags,
 	struct iomap		*iomap)
 {
-	fs_put_dax(iomap->dax_dev);
 	if ((flags & IOMAP_WRITE) && iomap->type == IOMAP_DELALLOC)
 		return xfs_file_iomap_end_delalloc(XFS_I(inode), offset,
 				length, written, iomap);
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 38aaacdbb8b3..d863f96b16e2 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -716,13 +716,19 @@ xfs_close_devices(
 {
 	if (mp->m_logdev_targp && mp->m_logdev_targp != mp->m_ddev_targp) {
 		struct block_device *logdev = mp->m_logdev_targp->bt_bdev;
+		struct dax_device *dax_logdev = mp->m_logdev_targp->bt_daxdev;
+
 		xfs_free_buftarg(mp, mp->m_logdev_targp);
 		xfs_blkdev_put(logdev);
+		fs_put_dax(dax_logdev);
 	}
 	if (mp->m_rtdev_targp) {
 		struct block_device *rtdev = mp->m_rtdev_targp->bt_bdev;
+		struct dax_device *dax_rtdev = mp->m_rtdev_targp->bt_daxdev;
+
 		xfs_free_buftarg(mp, mp->m_rtdev_targp);
 		xfs_blkdev_put(rtdev);
+		fs_put_dax(dax_rtdev);
 	}
 	xfs_free_buftarg(mp, mp->m_ddev_targp);
 }
@@ -742,7 +748,9 @@ xfs_open_devices(
 	struct xfs_mount	*mp)
 {
 	struct block_device	*ddev = mp->m_super->s_bdev;
+	struct dax_device	*dax_ddev = mp->m_super->s_daxdev;
 	struct block_device	*logdev = NULL, *rtdev = NULL;
+	struct dax_device	*dax_logdev = NULL, *dax_rtdev = NULL;
 	int			error;
 
 	/*
@@ -752,6 +760,7 @@ xfs_open_devices(
 		error = xfs_blkdev_get(mp, mp->m_logname, &logdev);
 		if (error)
 			goto out;
+		dax_logdev = fs_dax_get_by_bdev(logdev);
 	}
 
 	if (mp->m_rtname) {
@@ -765,24 +774,25 @@ xfs_open_devices(
 			error = -EINVAL;
 			goto out_close_rtdev;
 		}
+		dax_rtdev = fs_dax_get_by_bdev(rtdev);
 	}
 
 	/*
 	 * Setup xfs_mount buffer target pointers
 	 */
 	error = -ENOMEM;
-	mp->m_ddev_targp = xfs_alloc_buftarg(mp, ddev);
+	mp->m_ddev_targp = xfs_alloc_buftarg(mp, ddev, dax_ddev);
 	if (!mp->m_ddev_targp)
 		goto out_close_rtdev;
 
 	if (rtdev) {
-		mp->m_rtdev_targp = xfs_alloc_buftarg(mp, rtdev);
+		mp->m_rtdev_targp = xfs_alloc_buftarg(mp, rtdev, dax_rtdev);
 		if (!mp->m_rtdev_targp)
 			goto out_free_ddev_targ;
 	}
 
 	if (logdev && logdev != ddev) {
-		mp->m_logdev_targp = xfs_alloc_buftarg(mp, logdev);
+		mp->m_logdev_targp = xfs_alloc_buftarg(mp, logdev, dax_logdev);
 		if (!mp->m_logdev_targp)
 			goto out_free_rtdev_targ;
 	} else {
@@ -798,9 +808,12 @@ xfs_open_devices(
 	xfs_free_buftarg(mp, mp->m_ddev_targp);
  out_close_rtdev:
 	xfs_blkdev_put(rtdev);
+	fs_put_dax(dax_rtdev);
  out_close_logdev:
-	if (logdev && logdev != ddev)
+	if (logdev && logdev != ddev) {
 		xfs_blkdev_put(logdev);
+		fs_put_dax(dax_logdev);
+	}
  out:
 	return error;
 }
diff --git a/include/linux/dax.h b/include/linux/dax.h
index df97b7af7e2c..6e32be3badec 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -57,6 +57,7 @@ static inline void fs_put_dax(struct dax_device *dax_dev)
 	put_dax(dax_dev);
 }
 
+struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev);
 #else
 static inline int bdev_dax_supported(struct super_block *sb, int blocksize)
 {
@@ -71,6 +72,11 @@ static inline struct dax_device *fs_dax_get_by_host(const char *host)
 static inline void fs_put_dax(struct dax_device *dax_dev)
 {
 }
+
+struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
+{
+	return NULL;
+}
 #endif
 
 int dax_read_lock(void);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6e1fd5d21248..d0e3234a1fae 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1334,6 +1334,7 @@ struct super_block {
 	struct hlist_bl_head	s_anon;		/* anonymous dentries for (nfs) exporting */
 	struct list_head	s_mounts;	/* list of mounts; _not_ for fs use */
 	struct block_device	*s_bdev;
+	struct dax_device	*s_daxdev;
 	struct backing_dev_info *s_bdi;
 	struct mtd_info		*s_mtd;
 	struct hlist_node	s_instances;

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