Re: [PATCH] fs, dax: unify IOMAP_F_DIRTY read vs write handling policy in the dax core

[Jan Kara]

On Mon 13-11-17 17:27:54, Dan Williams wrote:
> While reviewing whether MAP_SYNC should strengthen its current guarantee
> of syncing writes from the initiating process to also include
> third-party readers observing dirty metadata, Dave pointed out that the
> check of IOMAP_WRITE is misplaced.
> 
> The policy of what to with IOMAP_F_DIRTY should be separated from the
> generic filesystem mechanism of reporting dirty metadata. Move this
> policy to the fs-dax core to simplify the per-filesystem iomap handlers,
> and further centralize code that implements the MAP_SYNC policy. This
> otherwise should not change behavior, it just makes it easier to change
> behavior in the future.
> 
> Cc: Jan Kara 
> Cc: Christoph Hellwig 
> Cc: Darrick J. Wong 
> Cc: Ross Zwisler 
> Reported-by: Dave Chinner 
> Signed-off-by: Dan Williams 
> ---
> This is an additional cleanup I want to include in the 4.15 merge
> request for the MAP_SYNC feature. Please review, I'm looking to send the
> pull request towards the end of the week.

The patch looks fine to me. You can add:

Reviewed-by: Jan Kara 

Honza

> 
> 
>  fs/dax.c   |   15 +--
>  fs/ext4/inode.c|2 +-
>  fs/xfs/xfs_iomap.c |6 +++---
>  3 files changed, 17 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index 78233c716757..27ba300660ff 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1079,6 +1079,17 @@ static int dax_fault_return(int error)
>   return VM_FAULT_SIGBUS;
>  }
>  
> +/*
> + * MAP_SYNC on a dax mapping guarantees dirty metadata is
> + * flushed on write-faults (non-cow), but not read-faults.
> + */
> +static bool dax_fault_is_synchronous(unsigned long flags,
> + struct vm_area_struct *vma, struct iomap *iomap)
> +{
> + return (flags & IOMAP_WRITE) && (vma->vm_flags & VM_SYNC)
> + && (iomap->flags & IOMAP_F_DIRTY);
> +}
> +
>  static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
>  const struct iomap_ops *ops)
>  {
> @@ -1170,7 +1181,7 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, 
> pfn_t *pfnp,
>   goto finish_iomap;
>   }
>  
> - sync = (vma->vm_flags & VM_SYNC) && (iomap.flags & IOMAP_F_DIRTY);
> + sync = dax_fault_is_synchronous(flags, vma, );
>  
>   switch (iomap.type) {
>   case IOMAP_MAPPED:
> @@ -1390,7 +1401,7 @@ static int dax_iomap_pmd_fault(struct vm_fault *vmf, 
> pfn_t *pfnp,
>   if (iomap.offset + iomap.length < pos + PMD_SIZE)
>   goto finish_iomap;
>  
> - sync = (vma->vm_flags & VM_SYNC) && (iomap.flags & IOMAP_F_DIRTY);
> + sync = dax_fault_is_synchronous(iomap_flags, vma, );
>  
>   switch (iomap.type) {
>   case IOMAP_MAPPED:
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 13a198924a0f..ee4d907a4251 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3479,7 +3479,7 @@ static int ext4_iomap_begin(struct inode *inode, loff_t 
> offset, loff_t length,
>   }
>  
>   iomap->flags = 0;
> - if ((flags & IOMAP_WRITE) && ext4_inode_datasync_dirty(inode))
> + if (ext4_inode_datasync_dirty(inode))
>   iomap->flags |= IOMAP_F_DIRTY;
>   iomap->bdev = inode->i_sb->s_bdev;
>   iomap->dax_dev = sbi->s_daxdev;
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index b43be199fbdf..888b60189983 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -1087,9 +1087,9 @@ xfs_file_iomap_begin(
>   trace_xfs_iomap_found(ip, offset, length, 0, );
>   }
>  
> - if ((flags & IOMAP_WRITE) && xfs_ipincount(ip) &&
> - (ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP))
> - iomap->flags |= IOMAP_F_DIRTY;
> + if (xfs_ipincount(ip))
> + if (ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP)
> + iomap->flags |= IOMAP_F_DIRTY;
>  
>   xfs_bmbt_to_iomap(ip, iomap, );
>  
> 
-- 
Jan Kara 
SUSE Labs, CR
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Re: [PATCH] fs, dax: unify IOMAP_F_DIRTY read vs write handling policy in the dax core

[Christoph Hellwig]

> - if ((flags & IOMAP_WRITE) && xfs_ipincount(ip) &&
> - (ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP))
> - iomap->flags |= IOMAP_F_DIRTY;
> + if (xfs_ipincount(ip))
> + if (ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP)
> + iomap->flags |= IOMAP_F_DIRTY;

Please don't split up the conditional and make it harder to read.

With that fixed up this looks fine to me:

Reviewed-by: Christoph Hellwig 
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Re: [PATCH] fs, dax: unify IOMAP_F_DIRTY read vs write handling policy in the dax core

[Dave Chinner]

On Mon, Nov 13, 2017 at 05:27:54PM -0800, Dan Williams wrote:
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index b43be199fbdf..888b60189983 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -1087,9 +1087,9 @@ xfs_file_iomap_begin(
>   trace_xfs_iomap_found(ip, offset, length, 0, );
>   }
>  
> - if ((flags & IOMAP_WRITE) && xfs_ipincount(ip) &&
> - (ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP))
> - iomap->flags |= IOMAP_F_DIRTY;
> + if (xfs_ipincount(ip))
> + if (ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP)
> + iomap->flags |= IOMAP_F_DIRTY;

Please make a helper for this, and use it in xfs_file_fsync() where
the same dirty checks are done. e.g.

static inline bool
xfs_inode_need_fsync(struct xfs_inode *ip, bool datasync)
{
if (!xfs_ipincount(ip))
return false;
if (xfs_inode_clean(ip))
return false;
if (datasync &&
!(ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP))
return false;
return true;
}

Cheers,

Dave.
-- 
Dave Chinner
da...@fromorbit.com
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Re: [PATCH] fs, dax: unify IOMAP_F_DIRTY read vs write handling policy in the dax core

[Darrick J. Wong]

On Mon, Nov 13, 2017 at 05:27:54PM -0800, Dan Williams wrote:
> While reviewing whether MAP_SYNC should strengthen its current guarantee
> of syncing writes from the initiating process to also include
> third-party readers observing dirty metadata, Dave pointed out that the
> check of IOMAP_WRITE is misplaced.
> 
> The policy of what to with IOMAP_F_DIRTY should be separated from the
> generic filesystem mechanism of reporting dirty metadata. Move this
> policy to the fs-dax core to simplify the per-filesystem iomap handlers,
> and further centralize code that implements the MAP_SYNC policy. This
> otherwise should not change behavior, it just makes it easier to change
> behavior in the future.

Yes, this was what I was looking for on my last read-through. :)

> Cc: Jan Kara 
> Cc: Christoph Hellwig 
> Cc: Darrick J. Wong 
> Cc: Ross Zwisler 
> Reported-by: Dave Chinner 
> Signed-off-by: Dan Williams 
> ---
> This is an additional cleanup I want to include in the 4.15 merge
> request for the MAP_SYNC feature. Please review, I'm looking to send the
> pull request towards the end of the week.
> 
> 
>  fs/dax.c   |   15 +--
>  fs/ext4/inode.c|2 +-
>  fs/xfs/xfs_iomap.c |6 +++---
>  3 files changed, 17 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index 78233c716757..27ba300660ff 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1079,6 +1079,17 @@ static int dax_fault_return(int error)
>   return VM_FAULT_SIGBUS;
>  }
>  
> +/*
> + * MAP_SYNC on a dax mapping guarantees dirty metadata is
> + * flushed on write-faults (non-cow), but not read-faults.
> + */
> +static bool dax_fault_is_synchronous(unsigned long flags,
> + struct vm_area_struct *vma, struct iomap *iomap)
> +{
> + return (flags & IOMAP_WRITE) && (vma->vm_flags & VM_SYNC)
> + && (iomap->flags & IOMAP_F_DIRTY);
> +}
> +
>  static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
>  const struct iomap_ops *ops)
>  {
> @@ -1170,7 +1181,7 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, 
> pfn_t *pfnp,
>   goto finish_iomap;
>   }
>  
> - sync = (vma->vm_flags & VM_SYNC) && (iomap.flags & IOMAP_F_DIRTY);
> + sync = dax_fault_is_synchronous(flags, vma, );
>  
>   switch (iomap.type) {
>   case IOMAP_MAPPED:
> @@ -1390,7 +1401,7 @@ static int dax_iomap_pmd_fault(struct vm_fault *vmf, 
> pfn_t *pfnp,
>   if (iomap.offset + iomap.length < pos + PMD_SIZE)
>   goto finish_iomap;
>  
> - sync = (vma->vm_flags & VM_SYNC) && (iomap.flags & IOMAP_F_DIRTY);
> + sync = dax_fault_is_synchronous(iomap_flags, vma, );
>  
>   switch (iomap.type) {
>   case IOMAP_MAPPED:
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 13a198924a0f..ee4d907a4251 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3479,7 +3479,7 @@ static int ext4_iomap_begin(struct inode *inode, loff_t 
> offset, loff_t length,
>   }
>  
>   iomap->flags = 0;
> - if ((flags & IOMAP_WRITE) && ext4_inode_datasync_dirty(inode))
> + if (ext4_inode_datasync_dirty(inode))
>   iomap->flags |= IOMAP_F_DIRTY;
>   iomap->bdev = inode->i_sb->s_bdev;
>   iomap->dax_dev = sbi->s_daxdev;
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index b43be199fbdf..888b60189983 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -1087,9 +1087,9 @@ xfs_file_iomap_begin(
>   trace_xfs_iomap_found(ip, offset, length, 0, );
>   }
>  
> - if ((flags & IOMAP_WRITE) && xfs_ipincount(ip) &&
> - (ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP))
> - iomap->flags |= IOMAP_F_DIRTY;
> + if (xfs_ipincount(ip))
> + if (ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP)

Why not if (xfs_ipincount(ip) && (ip->... & ~XFS_ILOG_TIMESTAMP)) ?

Otherwise looks ok (just this patch, will rvb the rest separately),
Reviewed-by: Darrick J. Wong 

--D

> + iomap->flags |= IOMAP_F_DIRTY;
>  
>   xfs_bmbt_to_iomap(ip, iomap, );
>  
> 
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[PATCH] fs, dax: unify IOMAP_F_DIRTY read vs write handling policy in the dax core

[Dan Williams]

While reviewing whether MAP_SYNC should strengthen its current guarantee
of syncing writes from the initiating process to also include
third-party readers observing dirty metadata, Dave pointed out that the
check of IOMAP_WRITE is misplaced.

The policy of what to with IOMAP_F_DIRTY should be separated from the
generic filesystem mechanism of reporting dirty metadata. Move this
policy to the fs-dax core to simplify the per-filesystem iomap handlers,
and further centralize code that implements the MAP_SYNC policy. This
otherwise should not change behavior, it just makes it easier to change
behavior in the future.

Cc: Jan Kara 
Cc: Christoph Hellwig 
Cc: Darrick J. Wong 
Cc: Ross Zwisler 
Reported-by: Dave Chinner 
Signed-off-by: Dan Williams 
---
This is an additional cleanup I want to include in the 4.15 merge
request for the MAP_SYNC feature. Please review, I'm looking to send the
pull request towards the end of the week.


 fs/dax.c   |   15 +--
 fs/ext4/inode.c|2 +-
 fs/xfs/xfs_iomap.c |6 +++---
 3 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 78233c716757..27ba300660ff 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1079,6 +1079,17 @@ static int dax_fault_return(int error)
return VM_FAULT_SIGBUS;
 }
 
+/*
+ * MAP_SYNC on a dax mapping guarantees dirty metadata is
+ * flushed on write-faults (non-cow), but not read-faults.
+ */
+static bool dax_fault_is_synchronous(unsigned long flags,
+   struct vm_area_struct *vma, struct iomap *iomap)
+{
+   return (flags & IOMAP_WRITE) && (vma->vm_flags & VM_SYNC)
+   && (iomap->flags & IOMAP_F_DIRTY);
+}
+
 static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
   const struct iomap_ops *ops)
 {
@@ -1170,7 +1181,7 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, 
pfn_t *pfnp,
goto finish_iomap;
}
 
-   sync = (vma->vm_flags & VM_SYNC) && (iomap.flags & IOMAP_F_DIRTY);
+   sync = dax_fault_is_synchronous(flags, vma, );
 
switch (iomap.type) {
case IOMAP_MAPPED:
@@ -1390,7 +1401,7 @@ static int dax_iomap_pmd_fault(struct vm_fault *vmf, 
pfn_t *pfnp,
if (iomap.offset + iomap.length < pos + PMD_SIZE)
goto finish_iomap;
 
-   sync = (vma->vm_flags & VM_SYNC) && (iomap.flags & IOMAP_F_DIRTY);
+   sync = dax_fault_is_synchronous(iomap_flags, vma, );
 
switch (iomap.type) {
case IOMAP_MAPPED:
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 13a198924a0f..ee4d907a4251 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3479,7 +3479,7 @@ static int ext4_iomap_begin(struct inode *inode, loff_t 
offset, loff_t length,
}
 
iomap->flags = 0;
-   if ((flags & IOMAP_WRITE) && ext4_inode_datasync_dirty(inode))
+   if (ext4_inode_datasync_dirty(inode))
iomap->flags |= IOMAP_F_DIRTY;
iomap->bdev = inode->i_sb->s_bdev;
iomap->dax_dev = sbi->s_daxdev;
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index b43be199fbdf..888b60189983 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -1087,9 +1087,9 @@ xfs_file_iomap_begin(
trace_xfs_iomap_found(ip, offset, length, 0, );
}
 
-   if ((flags & IOMAP_WRITE) && xfs_ipincount(ip) &&
-   (ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP))
-   iomap->flags |= IOMAP_F_DIRTY;
+   if (xfs_ipincount(ip))
+   if (ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP)
+   iomap->flags |= IOMAP_F_DIRTY;
 
xfs_bmbt_to_iomap(ip, iomap, );
 

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