RE: [PATCH v6.1 6/7] fs/xfs: Handle CoW for fsdax write() path

[ruansy.fnst@xxxxxxxxxxx]

Hi Darrick,

Do you have any comment on this?


--
Thanks,
Ruan.

> -----Original Message-----
> From: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
> Subject: [PATCH v6.1 6/7] fs/xfs: Handle CoW for fsdax write() path
> 
> Hi Darrick,
> 
> Since other patches looks good, I post this RFC patch singly to hot-fix the
> problem in xfs_dax_write_iomap_ops->iomap_end() of v6 that the error code
> was ingored. I will split this in two patches(changes in iomap and xfs
> respectively) in next formal version if it looks ok.
> 
> ====
> 
> Introduce a new interface called "iomap_post_actor()" in iomap_ops.  And call
> it between ->actor() and ->iomap_end().  It is mean to handle the error code
> returned from ->actor().  In this patchset, it is used to remap or cancel the
> CoW extents according to the error code.
> 
> Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
> ---
>  fs/dax.c               | 27 ++++++++++++++++++---------
>  fs/iomap/apply.c       |  4 ++++
>  fs/xfs/xfs_bmap_util.c |  3 +--
>  fs/xfs/xfs_file.c      |  5 +++--
>  fs/xfs/xfs_iomap.c     | 33 ++++++++++++++++++++++++++++++++-
>  fs/xfs/xfs_iomap.h     | 24 ++++++++++++++++++++++++
>  fs/xfs/xfs_iops.c      |  7 +++----
>  fs/xfs/xfs_reflink.c   |  3 +--
>  include/linux/iomap.h  |  8 ++++++++
>  9 files changed, 94 insertions(+), 20 deletions(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index 93f16210847b..0740c2610b6f 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1537,7 +1537,7 @@ static vm_fault_t dax_iomap_pte_fault(struct
> vm_fault *vmf, pfn_t *pfnp,
>  	struct iomap iomap = { .type = IOMAP_HOLE };
>  	struct iomap srcmap = { .type = IOMAP_HOLE };
>  	unsigned flags = IOMAP_FAULT;
> -	int error;
> +	int error, copied = PAGE_SIZE;
>  	bool write = vmf->flags & FAULT_FLAG_WRITE;
>  	vm_fault_t ret = 0, major = 0;
>  	void *entry;
> @@ -1598,7 +1598,7 @@ static vm_fault_t dax_iomap_pte_fault(struct
> vm_fault *vmf, pfn_t *pfnp,
>  	ret = dax_fault_actor(vmf, pfnp, &xas, &entry, false, flags,
>  			      &iomap, &srcmap);
>  	if (ret == VM_FAULT_SIGBUS)
> -		goto finish_iomap;
> +		goto finish_iomap_actor;
> 
>  	/* read/write MAPPED, CoW UNWRITTEN */
>  	if (iomap.flags & IOMAP_F_NEW) {
> @@ -1607,10 +1607,16 @@ static vm_fault_t dax_iomap_pte_fault(struct
> vm_fault *vmf, pfn_t *pfnp,
>  		major = VM_FAULT_MAJOR;
>  	}
> 
> + finish_iomap_actor:
> +	if (ops->iomap_post_actor) {
> +		if (ret & VM_FAULT_ERROR)
> +			copied = 0;
> +		ops->iomap_post_actor(inode, pos, PMD_SIZE, copied, flags,
> +				      &iomap, &srcmap);
> +	}
> +
>  finish_iomap:
>  	if (ops->iomap_end) {
> -		int copied = PAGE_SIZE;
> -
>  		if (ret & VM_FAULT_ERROR)
>  			copied = 0;
>  		/*
> @@ -1677,7 +1683,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct
> vm_fault *vmf, pfn_t *pfnp,
>  	pgoff_t max_pgoff;
>  	void *entry;
>  	loff_t pos;
> -	int error;
> +	int error, copied = PMD_SIZE;
> 
>  	/*
>  	 * Check whether offset isn't beyond end of file now. Caller is @@ -1736,12
> +1742,15 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf,
> pfn_t *pfnp,
>  	ret = dax_fault_actor(vmf, pfnp, &xas, &entry, true, flags,
>  			      &iomap, &srcmap);
> 
> +	if (ret == VM_FAULT_FALLBACK)
> +		copied = 0;
> +	if (ops->iomap_post_actor) {
> +		ops->iomap_post_actor(inode, pos, PMD_SIZE, copied, flags,
> +				      &iomap, &srcmap);
> +	}
> +
>  finish_iomap:
>  	if (ops->iomap_end) {
> -		int copied = PMD_SIZE;
> -
> -		if (ret == VM_FAULT_FALLBACK)
> -			copied = 0;
>  		/*
>  		 * The fault is done by now and there's no way back (other
>  		 * thread may be already happily using PMD we have installed).
> diff --git a/fs/iomap/apply.c b/fs/iomap/apply.c index
> 0493da5286ad..26a54ded184f 100644
> --- a/fs/iomap/apply.c
> +++ b/fs/iomap/apply.c
> @@ -84,6 +84,10 @@ iomap_apply(struct inode *inode, loff_t pos, loff_t length,
> unsigned flags,
>  	written = actor(inode, pos, length, data, &iomap,
>  			srcmap.type != IOMAP_HOLE ? &srcmap : &iomap);
> 
> +	if (ops->iomap_post_actor) {
> +		written = ops->iomap_post_actor(inode, pos, length, written,
> +						flags, &iomap, &srcmap);
> +	}
>  out:
>  	/*
>  	 * Now the data has been copied, commit the range we've copied.  This
> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c index
> a5e9d7d34023..2a36dc93ff27 100644
> --- a/fs/xfs/xfs_bmap_util.c
> +++ b/fs/xfs/xfs_bmap_util.c
> @@ -965,8 +965,7 @@ xfs_free_file_space(
>  		return 0;
>  	if (offset + len > XFS_ISIZE(ip))
>  		len = XFS_ISIZE(ip) - offset;
> -	error = iomap_zero_range(VFS_I(ip), offset, len, NULL,
> -			&xfs_buffered_write_iomap_ops);
> +	error = xfs_iomap_zero_range(ip, offset, len, NULL);
>  	if (error)
>  		return error;
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c index 396ef36dcd0a..89406ec6741b
> 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -684,11 +684,12 @@ xfs_file_dax_write(
>  	pos = iocb->ki_pos;
> 
>  	trace_xfs_file_dax_write(iocb, from);
> -	ret = dax_iomap_rw(iocb, from, &xfs_direct_write_iomap_ops);
> +	ret = dax_iomap_rw(iocb, from, &xfs_dax_write_iomap_ops);
>  	if (ret > 0 && iocb->ki_pos > i_size_read(inode)) {
>  		i_size_write(inode, iocb->ki_pos);
>  		error = xfs_setfilesize(ip, pos, ret);
>  	}
> +
>  out:
>  	if (iolock)
>  		xfs_iunlock(ip, iolock);
> @@ -1309,7 +1310,7 @@ __xfs_filemap_fault(
> 
>  		ret = dax_iomap_fault(vmf, pe_size, &pfn, NULL,
>  				(write_fault && !vmf->cow_page) ?
> -				 &xfs_direct_write_iomap_ops :
> +				 &xfs_dax_write_iomap_ops :
>  				 &xfs_read_iomap_ops);
>  		if (ret & VM_FAULT_NEEDDSYNC)
>  			ret = dax_finish_sync_fault(vmf, pe_size, pfn); diff --git
> a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c index d154f42e2dc6..2f322e2f8544
> 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -761,7 +761,8 @@ xfs_direct_write_iomap_begin(
> 
>  		/* may drop and re-acquire the ilock */
>  		error = xfs_reflink_allocate_cow(ip, &imap, &cmap, &shared,
> -				&lockmode, flags & IOMAP_DIRECT);
> +				&lockmode,
> +				(flags & IOMAP_DIRECT) || IS_DAX(inode));
>  		if (error)
>  			goto out_unlock;
>  		if (shared)
> @@ -854,6 +855,36 @@ const struct iomap_ops xfs_direct_write_iomap_ops =
> {
>  	.iomap_begin		= xfs_direct_write_iomap_begin,
>  };
> 
> +static int
> +xfs_dax_write_iomap_post_actor(
> +	struct inode		*inode,
> +	loff_t			pos,
> +	loff_t			length,
> +	ssize_t			written,
> +	unsigned int		flags,
> +	struct iomap		*iomap,
> +	struct iomap		*srcmap)
> +{
> +	int			error = 0;
> +	struct xfs_inode	*ip = XFS_I(inode);
> +	bool			cow = xfs_is_cow_inode(ip);
> +
> +	if (written <= 0) {
> +		if (cow)
> +			xfs_reflink_cancel_cow_range(ip, pos, length, true);
> +		return written;
> +	}
> +
> +	if (cow)
> +		error = xfs_reflink_end_cow(ip, pos, written);
> +	return error ?: written;
> +}
> +
> +const struct iomap_ops xfs_dax_write_iomap_ops = {
> +	.iomap_begin		= xfs_direct_write_iomap_begin,
> +	.iomap_post_actor	= xfs_dax_write_iomap_post_actor,
> +};
> +
>  static int
>  xfs_buffered_write_iomap_begin(
>  	struct inode		*inode,
> diff --git a/fs/xfs/xfs_iomap.h b/fs/xfs/xfs_iomap.h index
> 7d3703556d0e..fbacf638ab21 100644
> --- a/fs/xfs/xfs_iomap.h
> +++ b/fs/xfs/xfs_iomap.h
> @@ -42,8 +42,32 @@ xfs_aligned_fsb_count(
> 
>  extern const struct iomap_ops xfs_buffered_write_iomap_ops;  extern const
> struct iomap_ops xfs_direct_write_iomap_ops;
> +extern const struct iomap_ops xfs_dax_write_iomap_ops;
>  extern const struct iomap_ops xfs_read_iomap_ops;  extern const struct
> iomap_ops xfs_seek_iomap_ops;  extern const struct iomap_ops
> xfs_xattr_iomap_ops;
> 
> +static inline int
> +xfs_iomap_zero_range(
> +	struct xfs_inode	*ip,
> +	loff_t			offset,
> +	loff_t			len,
> +	bool			*did_zero)
> +{
> +	return iomap_zero_range(VFS_I(ip), offset, len, did_zero,
> +			IS_DAX(VFS_I(ip)) ? &xfs_dax_write_iomap_ops
> +					  : &xfs_buffered_write_iomap_ops); }
> +
> +static inline int
> +xfs_iomap_truncate_page(
> +	struct xfs_inode	*ip,
> +	loff_t			pos,
> +	bool			*did_zero)
> +{
> +	return iomap_truncate_page(VFS_I(ip), pos, did_zero,
> +			IS_DAX(VFS_I(ip)) ? &xfs_dax_write_iomap_ops
> +					  : &xfs_buffered_write_iomap_ops); }
> +
>  #endif /* __XFS_IOMAP_H__*/
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c index
> dfe24b7f26e5..6d936c3e1a6e 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -911,8 +911,8 @@ xfs_setattr_size(
>  	 */
>  	if (newsize > oldsize) {
>  		trace_xfs_zero_eof(ip, oldsize, newsize - oldsize);
> -		error = iomap_zero_range(inode, oldsize, newsize - oldsize,
> -				&did_zeroing, &xfs_buffered_write_iomap_ops);
> +		error = xfs_iomap_zero_range(ip, oldsize, newsize - oldsize,
> +				&did_zeroing);
>  	} else {
>  		/*
>  		 * iomap won't detect a dirty page over an unwritten block (or a @@
> -924,8 +924,7 @@ xfs_setattr_size(
>  						     newsize);
>  		if (error)
>  			return error;
> -		error = iomap_truncate_page(inode, newsize, &did_zeroing,
> -				&xfs_buffered_write_iomap_ops);
> +		error = xfs_iomap_truncate_page(ip, newsize, &did_zeroing);
>  	}
> 
>  	if (error)
> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c index
> d25434f93235..9a780948dbd0 100644
> --- a/fs/xfs/xfs_reflink.c
> +++ b/fs/xfs/xfs_reflink.c
> @@ -1266,8 +1266,7 @@ xfs_reflink_zero_posteof(
>  		return 0;
> 
>  	trace_xfs_zero_eof(ip, isize, pos - isize);
> -	return iomap_zero_range(VFS_I(ip), isize, pos - isize, NULL,
> -			&xfs_buffered_write_iomap_ops);
> +	return xfs_iomap_zero_range(ip, isize, pos - isize, NULL);
>  }
> 
>  /*
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h index
> 95562f863ad0..58f2e1c78018 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -135,6 +135,14 @@ struct iomap_ops {
>  			unsigned flags, struct iomap *iomap,
>  			struct iomap *srcmap);
> 
> +	/*
> +	 * Handle the error code from actor(). Do the finishing jobs for extra
> +	 * operations, such as CoW, according to whether written is negative.
> +	 */
> +	int (*iomap_post_actor)(struct inode *inode, loff_t pos, loff_t length,
> +			ssize_t written, unsigned flags, struct iomap *iomap,
> +			struct iomap *srcmap);
> +
>  	/*
>  	 * Commit and/or unreserve space previous allocated using iomap_begin.
>  	 * Written indicates the length of the successful write operation which
> --
> 2.31.1