Re: [PATCH v8 14/17] iomap: Add done_before argument to iomap_dio_rw

Darrick J. Wong
2021-10-19T15:51:36Z

On Tue, Oct 19, 2021 at 03:42:01PM +0200, Andreas Gruenbacher wrote:
> Add a done_before argument to iomap_dio_rw that indicates how much of
> the request has already been transferred. When the request succeeds, we
> report that done_before additional bytes were tranferred. This is
> useful for finishing a request asynchronously when part of the request
> has already been completed synchronously.
>
> We'll use that to allow iomap_dio_rw to be used with page faults
> disabled: when a page fault occurs while submitting a request, we
> synchronously complete the part of the request that has already been
> submitted. The caller can then take care of the page fault and call
> iomap_dio_rw again for the rest of the request, passing in the number of
> bytes already tranferred.
>
> Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
> ---
> fs/btrfs/file.c | 5 +++--
> fs/erofs/data.c | 2 +-
> fs/ext4/file.c | 5 +++--
> fs/gfs2/file.c | 4 ++--
> fs/iomap/direct-io.c | 11 ++++++++---
> fs/xfs/xfs_file.c | 6 +++---
> fs/zonefs/super.c | 4 ++--
> include/linux/iomap.h | 4 ++--
> 8 files changed, 24 insertions(+), 17 deletions(-)
>
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index f37211d3bb69..9d41b28c67ba 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -1957,7 +1957,7 @@ static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from)
> }
>
> dio = __iomap_dio_rw(iocb, from, &btrfs_dio_iomap_ops, &btrfs_dio_ops,
> - 0);
> + 0, 0);
>
> btrfs_inode_unlock(inode, ilock_flags);
>
> @@ -3658,7 +3658,8 @@ static ssize_t btrfs_direct_read(struct kiocb *iocb, struct iov_iter *to)
> return 0;
>
> btrfs_inode_lock(inode, BTRFS_ILOCK_SHARED);
> - ret = iomap_dio_rw(iocb, to, &btrfs_dio_iomap_ops, &btrfs_dio_ops, 0);
> + ret = iomap_dio_rw(iocb, to, &btrfs_dio_iomap_ops, &btrfs_dio_ops,
> + 0, 0);
> btrfs_inode_unlock(inode, BTRFS_ILOCK_SHARED);
> return ret;
> }
> diff --git a/fs/erofs/data.c b/fs/erofs/data.c
> index 9db829715652..16a41d0db55a 100644
> --- a/fs/erofs/data.c
> +++ b/fs/erofs/data.c
> @@ -287,7 +287,7 @@ static ssize_t erofs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
>
> if (!err)
> return iomap_dio_rw(iocb, to, &erofs_iomap_ops,
> - NULL, 0);
> + NULL, 0, 0);
> if (err < 0)
> return err;
> }
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index ac0e11bbb445..b25c1f8f7c4f 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -74,7 +74,7 @@ static ssize_t ext4_dio_read_iter(struct kiocb *iocb, struct iov_iter *to)
> return generic_file_read_iter(iocb, to);
> }
>
> - ret = iomap_dio_rw(iocb, to, &ext4_iomap_ops, NULL, 0);
> + ret = iomap_dio_rw(iocb, to, &ext4_iomap_ops, NULL, 0, 0);
> inode_unlock_shared(inode);
>
> file_accessed(iocb->ki_filp);
> @@ -566,7 +566,8 @@ static ssize_t ext4_dio_write_iter(struct kiocb *iocb, struct iov_iter *from)
> if (ilock_shared)
> iomap_ops = &ext4_iomap_overwrite_ops;
> ret = iomap_dio_rw(iocb, from, iomap_ops, &ext4_dio_write_ops,
> - (unaligned_io || extend) ? IOMAP_DIO_FORCE_WAIT : 0);
> + (unaligned_io || extend) ? IOMAP_DIO_FORCE_WAIT : 0,
> + 0);
> if (ret == -ENOTBLK)
> ret = 0;
>
> diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
> index b07b9c2d0446..ae06defcf369 100644
> --- a/fs/gfs2/file.c
> +++ b/fs/gfs2/file.c
> @@ -822,7 +822,7 @@ static ssize_t gfs2_file_direct_read(struct kiocb *iocb, struct iov_iter *to,
> if (ret)
> goto out_uninit;
>
> - ret = iomap_dio_rw(iocb, to, &gfs2_iomap_ops, NULL, 0);
> + ret = iomap_dio_rw(iocb, to, &gfs2_iomap_ops, NULL, 0, 0);
> gfs2_glock_dq(gh);
> out_uninit:
> gfs2_holder_uninit(gh);
> @@ -856,7 +856,7 @@ static ssize_t gfs2_file_direct_write(struct kiocb *iocb, struct iov_iter *from,
> if (offset + len > i_size_read(&ip->i_inode))
> goto out;
>
> - ret = iomap_dio_rw(iocb, from, &gfs2_iomap_ops, NULL, 0);
> + ret = iomap_dio_rw(iocb, from, &gfs2_iomap_ops, NULL, 0, 0);
> if (ret == -ENOTBLK)
> ret = 0;
> out:
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index a434fb7887b2..fdf68339bc8b 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -31,6 +31,7 @@ struct iomap_dio {
> atomic_t ref;
> unsigned flags;
> int error;
> + size_t done_before;

I have basically the same comment as last time[1]:

"So, now that I actually understand the reason why the count of
previously transferred bytes has to be passed into the iomap_dio, I
would like this field to have a comment so that stupid maintainers like
me don't forget the subtleties again:

/*
* For asynchronous IO, we have one chance to call the iocb
* completion method with the results of the directio operation.
* If this operation is a resubmission after a previous partial
* completion (e.g. page fault), we need to know about that
* progress so that we can report both the results of the prior
* completion and the result of the resubmission to the iocb
* submitter.
*/
size_t done_before;

With that added, I think I can live with this enough to:
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

[1] https://lore.kernel.org/linux-fsdevel/20210903185351.GD9892@magnolia/

> bool wait_for_completion;
>
> union {
> @@ -124,6 +125,9 @@ ssize_t iomap_dio_complete(struct iomap_dio *dio)
> if (ret > 0 && (dio->flags & IOMAP_DIO_NEED_SYNC))
> ret = generic_write_sync(iocb, ret);
>
> + if (ret > 0)
> + ret += dio->done_before;
> +
> kfree(dio);
>
> return ret;
> @@ -456,7 +460,7 @@ static loff_t iomap_dio_iter(const struct iomap_iter *iter,
> struct iomap_dio *
> __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> const struct iomap_ops *ops, const struct iomap_dio_ops *dops,
> - unsigned int dio_flags)
> + unsigned int dio_flags, size_t done_before)
> {
> struct address_space *mapping = iocb->ki_filp->f_mapping;
> struct inode *inode = file_inode(iocb->ki_filp);
> @@ -486,6 +490,7 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> dio->dops = dops;
> dio->error = 0;
> dio->flags = 0;
> + dio->done_before = done_before;
>
> dio->submit.iter = iter;
> dio->submit.waiter = current;
> @@ -652,11 +657,11 @@ EXPORT_SYMBOL_GPL(__iomap_dio_rw);
> ssize_t
> iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> const struct iomap_ops *ops, const struct iomap_dio_ops *dops,
> - unsigned int dio_flags)
> + unsigned int dio_flags, size_t done_before)
> {
> struct iomap_dio *dio;
>
> - dio = __iomap_dio_rw(iocb, iter, ops, dops, dio_flags);
> + dio = __iomap_dio_rw(iocb, iter, ops, dops, dio_flags, done_before);
> if (IS_ERR_OR_NULL(dio))
> return PTR_ERR_OR_ZERO(dio);
> return iomap_dio_complete(dio);
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 7aa943edfc02..240eb932c014 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -259,7 +259,7 @@ xfs_file_dio_read(
> ret = xfs_ilock_iocb(iocb, XFS_IOLOCK_SHARED);
> if (ret)
> return ret;
> - ret = iomap_dio_rw(iocb, to, &xfs_read_iomap_ops, NULL, 0);
> + ret = iomap_dio_rw(iocb, to, &xfs_read_iomap_ops, NULL, 0, 0);
> xfs_iunlock(ip, XFS_IOLOCK_SHARED);
>
> return ret;
> @@ -569,7 +569,7 @@ xfs_file_dio_write_aligned(
> }
> trace_xfs_file_direct_write(iocb, from);
> ret = iomap_dio_rw(iocb, from, &xfs_direct_write_iomap_ops,
> - &xfs_dio_write_ops, 0);
> + &xfs_dio_write_ops, 0, 0);
> out_unlock:
> if (iolock)
> xfs_iunlock(ip, iolock);
> @@ -647,7 +647,7 @@ xfs_file_dio_write_unaligned(
>
> trace_xfs_file_direct_write(iocb, from);
> ret = iomap_dio_rw(iocb, from, &xfs_direct_write_iomap_ops,
> - &xfs_dio_write_ops, flags);
> + &xfs_dio_write_ops, flags, 0);
>
> /*
> * Retry unaligned I/O with exclusive blocking semantics if the DIO
> diff --git a/fs/zonefs/super.c b/fs/zonefs/super.c
> index ddc346a9df9b..6122c38ab44d 100644
> --- a/fs/zonefs/super.c
> +++ b/fs/zonefs/super.c
> @@ -852,7 +852,7 @@ static ssize_t zonefs_file_dio_write(struct kiocb *iocb, struct iov_iter *from)
> ret = zonefs_file_dio_append(iocb, from);
> else
> ret = iomap_dio_rw(iocb, from, &zonefs_iomap_ops,
> - &zonefs_write_dio_ops, 0);
> + &zonefs_write_dio_ops, 0, 0);
> if (zi->i_ztype == ZONEFS_ZTYPE_SEQ &&
> (ret > 0 || ret == -EIOCBQUEUED)) {
> if (ret > 0)
> @@ -987,7 +987,7 @@ static ssize_t zonefs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
> }
> file_accessed(iocb->ki_filp);
> ret = iomap_dio_rw(iocb, to, &zonefs_iomap_ops,
> - &zonefs_read_dio_ops, 0);
> + &zonefs_read_dio_ops, 0, 0);
> } else {
> ret = generic_file_read_iter(iocb, to);
> if (ret == -EIO)
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 2a213b0d1e1f..829f2325ecba 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -339,10 +339,10 @@ struct iomap_dio_ops {
>
> ssize_t iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> const struct iomap_ops *ops, const struct iomap_dio_ops *dops,
> - unsigned int dio_flags);
> + unsigned int dio_flags, size_t done_before);
> struct iomap_dio *__iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> const struct iomap_ops *ops, const struct iomap_dio_ops *dops,
> - unsigned int dio_flags);
> + unsigned int dio_flags, size_t done_before);
> ssize_t iomap_dio_complete(struct iomap_dio *dio);
> int iomap_dio_iopoll(struct kiocb *kiocb, bool spin);
>
> --
> 2.26.3
>