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Date: Tue, 25 May 2021 17:21:03 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Shiyang Ruan <ruansy.fnst@...itsu.com>
Cc: linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
linux-nvdimm@...ts.01.org, linux-fsdevel@...r.kernel.org,
darrick.wong@...cle.com, dan.j.williams@...el.com,
willy@...radead.org, viro@...iv.linux.org.uk, david@...morbit.com,
hch@....de, rgoldwyn@...e.de
Subject: Re: [PATCH v6 6/7] fs/xfs: Handle CoW for fsdax write() path
On Wed, May 19, 2021 at 02:00:44PM +0800, Shiyang Ruan wrote:
> In fsdax mode, WRITE and ZERO on a shared extent need CoW performed. After
> CoW, new allocated extents needs to be remapped to the file. So, add an
> iomap_end for dax write ops to do the remapping work.
>
> Signed-off-by: Shiyang Ruan <ruansy.fnst@...itsu.com>
> ---
> fs/xfs/xfs_bmap_util.c | 3 +--
> fs/xfs/xfs_file.c | 9 +++------
> fs/xfs/xfs_iomap.c | 38 +++++++++++++++++++++++++++++++++++++-
> fs/xfs/xfs_iomap.h | 24 ++++++++++++++++++++++++
> fs/xfs/xfs_iops.c | 7 +++----
> fs/xfs/xfs_reflink.c | 3 +--
> 6 files changed, 69 insertions(+), 15 deletions(-)
>
> 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..38d8eca05aee 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -684,11 +684,8 @@ 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);
> - if (ret > 0 && iocb->ki_pos > i_size_read(inode)) {
> - i_size_write(inode, iocb->ki_pos);
> - error = xfs_setfilesize(ip, pos, ret);
> - }
> + ret = dax_iomap_rw(iocb, from, &xfs_dax_write_iomap_ops);
> +
> out:
> if (iolock)
> xfs_iunlock(ip, iolock);
> @@ -1309,7 +1306,7 @@ __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..938723aa137d 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 +855,41 @@ const struct iomap_ops xfs_direct_write_iomap_ops = {
> .iomap_begin = xfs_direct_write_iomap_begin,
> };
>
> +static int
> +xfs_dax_write_iomap_end(
> + struct inode *inode,
> + loff_t pos,
> + loff_t length,
> + ssize_t written,
> + unsigned int flags,
> + struct iomap *iomap)
> +{
> + int error = 0;
> + struct xfs_inode *ip = XFS_I(inode);
> + bool cow = xfs_is_cow_inode(ip);
> +
> + if (!written)
> + return 0;
> +
> + if (pos + written > i_size_read(inode) && !(flags & IOMAP_FAULT)) {
> + i_size_write(inode, pos + written);
> + error = xfs_setfilesize(ip, pos, written);
> + if (error && cow) {
> + xfs_reflink_cancel_cow_range(ip, pos, written, true);
> + return error;
> + }
> + }
> + if (cow)
> + error = xfs_reflink_end_cow(ip, pos, written);
> +
> + return error;
I think this (the ->iomap_end handler) is the wrong place to be
performing COW remapping, because of this chunk in iomap_apply:
/*
* Now the data has been copied, commit the range we've copied.
* This should not fail unless the filesystem has had a fatal
* error.
*/
if (ops->iomap_end) {
ret = ops->iomap_end(inode, pos, length,
written > 0 ? written : 0,
flags, &iomap);
}
return written ? written : ret;
If we managed to write something but the remap fails, we'll eat the
error message and return the length of the write to the caller.
Eventually the callers /may/ notice that they can still read old file
contents after a "successful" write.
I think what needs to happen here is that we call out to the filesystem
to remap the blocks at the end of dax_iomap_actor, similar to how the
iomap directio code calls xfs_dio_write_end_io after all of the write
bios complete. If the remap fails, we return that error out of
dax_iomap_actor, which will be returned to the caller as a short write
or an error code if nothing got written.
IOWs, the end of dax_iomap_actor should become:
/* dax_copy_{to,from}_iter calls here */
pos += xfer;
length -= xfer;
done += xfer;
if (xfer == 0)
ret = -EFAULT;
if (xfer < map_len)
break;
}
dax_read_unlock(id);
if (dops && dops->end_io) {
unsigned flags = 0;
if (srcmap->addr != iomap->addr)
flags |= IOMAP_DIO_COW;
ret = dops->end_io(iocb, done, ret, flags);
}
if (likely(!ret)) {
ret = done;
/* check for short read */
if (offset + ret > i_size_read(inode) && !write)
ret = i_size_read(inode) - offset;
iocb->ki_pos += ret;
}
return ret;
}
And I think you can even reuse the struct iomap_dio_ops and
xfs_dio_write_end_io for this purpose.
> +}
> +
> +const struct iomap_ops xfs_dax_write_iomap_ops = {
> + .iomap_begin = xfs_direct_write_iomap_begin,
> + .iomap_end = xfs_dax_write_iomap_end,
> +};
> +
> 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);
> }
>
> /*
> --
> 2.31.1
>
>
>
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