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From: "Darrick J. Wong" <djwong@kernel.org>
To: Andreas Gruenbacher <agruenba@redhat.com>
Cc: cluster-devel@redhat.com, Jan Kara <jack@suse.cz>,
	linux-kernel@vger.kernel.org,
	Christoph Hellwig <hch@infradead.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-fsdevel@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	ocfs2-devel@oss.oracle.com
Subject: Re: [Ocfs2-devel] [PATCH v7 16/19] iomap: Add done_before argument to iomap_dio_rw
Date: Fri, 27 Aug 2021 11:30:18 -0700	[thread overview]
Message-ID: <20210827183018.GJ12664@magnolia> (raw)
In-Reply-To: <20210827164926.1726765-17-agruenba@redhat.com>

On Fri, Aug 27, 2021 at 06:49:23PM +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/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 ++--
>  7 files changed, 23 insertions(+), 16 deletions(-)
> 

<snip to the interesting parts>

> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index ba88fe51b77a..dcf9a2b4381f 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;
>  	bool			wait_for_completion;
>  
>  	union {
> @@ -126,6 +127,9 @@ 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;

Pardon my ignorance since this is the first time I've had a crack at
this patchset, but why is it necessary to carry the "bytes copied"
count from the /previous/ iomap_dio_rw call all the way through to dio
completion of the current call?

If the directio operation succeeds even partially and the PARTIAL flag
is set, won't that push the iov iter ahead by however many bytes
completed?

In other words, why won't this loop work for gfs2?

	size_t copied = 0;
	while (iov_iter_count(iov) > 0) {
		ssize_t ret = iomap_dio_rw(iocb, iov, ..., IOMAP_DIO_PARTIAL);
		if (iov_iter_count(iov) == 0 || ret != -EFAULT)
			break;

		copied += ret;
		/* strange gfs2 relocking I don't understand */
		/* deal with page faults... */
	};
	if (ret < 0)
		return ret;
	return copied + ret;

It feels clunky to make the caller pass the results of a previous
operation through the current operation just so the caller can catch the
value again afterwards.  Is there something I'm missing?

--D

> +
>  	kfree(dio);
>  
>  	return ret;
> @@ -450,7 +454,7 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
>  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);
> @@ -477,6 +481,7 @@ __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;
> @@ -648,11 +653,11 @@ 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 cc3cfb12df53..3103d9bda466 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 70055d486bf7..85ca2f5fe06e 100644
> --- a/fs/zonefs/super.c
> +++ b/fs/zonefs/super.c
> @@ -864,7 +864,7 @@ 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)
> @@ -999,7 +999,7 @@ 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 bcae4814b8e3..908bda10024c 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -276,10 +276,10 @@ 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
> 

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  reply	other threads:[~2021-08-27 18:30 UTC|newest]

Thread overview: 100+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-27 16:49 [Ocfs2-devel] [PATCH v7 00/19] gfs2: Fix mmap + page fault deadlocks Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 01/19] iov_iter: Fix iov_iter_get_pages{, _alloc} page fault return value Andreas Gruenbacher
2021-09-09 11:09   ` Christoph Hellwig
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 02/19] powerpc/kvm: Fix kvm_use_magic_page Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 03/19] gup: Turn fault_in_pages_{readable, writeable} into fault_in_{readable, writeable} Andreas Gruenbacher
2021-08-27 19:08   ` Al Viro
2021-09-03 14:56   ` Filipe Manana
2021-09-28 15:02     ` Andreas Gruenbacher
2021-09-28 16:37       ` Matthew Wilcox
2021-09-28 20:41         ` Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 04/19] iov_iter: Turn iov_iter_fault_in_readable into fault_in_iov_iter_readable Andreas Gruenbacher
2021-08-27 18:53   ` Al Viro
2021-08-27 18:57     ` Linus Torvalds
2021-08-27 19:16       ` Al Viro
2021-08-27 20:56   ` Kari Argillander
2021-08-28 17:13     ` Linus Torvalds
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable Andreas Gruenbacher
2021-08-27 18:49   ` Al Viro
2021-08-27 19:05     ` Linus Torvalds
2021-08-27 19:23       ` Al Viro
2021-08-27 19:33         ` Linus Torvalds
2021-08-27 19:37           ` Al Viro
2021-08-27 21:48             ` Al Viro
2021-08-27 21:57               ` Al Viro
2021-08-27 23:22                 ` Luck, Tony
2021-08-28  2:20                   ` Luck, Tony
2021-08-28 21:47                   ` Thomas Gleixner
2021-08-28 22:04                     ` Al Viro
2021-08-28 22:11                       ` Al Viro
2021-08-28 22:19                         ` Al Viro
2021-08-28 22:51                           ` Al Viro
2021-08-29 18:44                             ` Thomas Gleixner
2021-08-29 19:46                               ` Al Viro
2021-08-29 19:51                                 ` Thomas Gleixner
2021-08-28 22:20                         ` Tony Luck
2021-08-29  1:40                           ` Matthew Wilcox
2021-08-30 15:41                             ` Luck, Tony
2021-08-28 22:23                       ` Thomas Gleixner
2021-08-28 19:28               ` [Ocfs2-devel] [RFC][arm64] possible infinite loop in btrfs search_ioctl() Al Viro
2021-08-31 13:54                 ` Catalin Marinas
2021-08-31 15:28                   ` Al Viro
2021-08-31 16:01                     ` Catalin Marinas
2021-10-11 17:37                     ` Catalin Marinas
2021-10-11 19:15                       ` Linus Torvalds
2021-10-11 21:08                         ` Catalin Marinas
2021-10-11 23:59                           ` Linus Torvalds
2021-10-12 17:27                             ` Catalin Marinas
2021-10-12 17:58                               ` Linus Torvalds
2021-10-18 17:13                                 ` Catalin Marinas
2021-10-21  0:46                             ` Andreas Gruenbacher
2021-10-21 10:05                               ` Catalin Marinas
2021-10-21 14:42                                 ` Andreas Gruenbacher
2021-10-21 17:09                                   ` Catalin Marinas
2021-10-21 18:00                                     ` Andreas Gruenbacher
2021-10-22 18:41                                       ` Catalin Marinas
2021-10-25 19:37                                         ` Andreas Gruenbacher
2021-10-22  2:30                                   ` Linus Torvalds
2021-10-22  9:34                                     ` Catalin Marinas
2021-08-29  0:58               ` [Ocfs2-devel] [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable Al Viro
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 06/19] gfs2: Add wrapper for iomap_file_buffered_write Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 07/19] gfs2: Clean up function may_grant Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 08/19] gfs2: Eliminate vestigial HIF_FIRST Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 09/19] gfs2: Remove redundant check from gfs2_glock_dq Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 10/19] gfs2: Introduce flag for glock holder auto-demotion Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 11/19] gfs2: Move the inode glock locking to gfs2_file_buffered_write Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 12/19] gfs2: Eliminate ip->i_gh Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 13/19] gfs2: Fix mmap + page fault deadlocks for buffered I/O Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 14/19] iomap: Fix iomap_dio_rw return value for user copies Andreas Gruenbacher
2021-09-03 18:54   ` Darrick J. Wong
2021-09-09 11:17   ` Christoph Hellwig
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 15/19] iomap: Support partial direct I/O on user copy failures Andreas Gruenbacher
2021-09-03 18:54   ` Darrick J. Wong
2021-09-09 11:20   ` Christoph Hellwig
2021-09-28 15:05     ` Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 16/19] iomap: Add done_before argument to iomap_dio_rw Andreas Gruenbacher
2021-08-27 18:30   ` Darrick J. Wong [this message]
2021-08-27 20:15     ` Andreas Gruenbacher
2021-08-27 21:32       ` Darrick J. Wong
2021-08-27 21:49         ` Andreas Grünbacher
2021-08-27 22:35         ` Linus Torvalds
2021-09-03 18:47           ` Darrick J. Wong
2021-09-03 18:53   ` Darrick J. Wong
2021-09-09 11:30   ` Christoph Hellwig
2021-09-09 17:22     ` Linus Torvalds
2021-09-10  7:36       ` Christoph Hellwig
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 17/19] gup: Introduce FOLL_NOFAULT flag to disable page faults Andreas Gruenbacher
2021-09-09 11:36   ` Christoph Hellwig
2021-09-09 17:17     ` Linus Torvalds
2021-09-10  7:24       ` Christoph Hellwig
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 18/19] iov_iter: Introduce nofault " Andreas Gruenbacher
2021-08-27 18:47   ` Al Viro
2021-08-27 19:56     ` Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 19/19] gfs2: Fix mmap + page fault deadlocks for direct I/O Andreas Gruenbacher
2021-08-27 17:16 ` [Ocfs2-devel] [PATCH v7 00/19] gfs2: Fix mmap + page fault deadlocks Linus Torvalds
2021-09-01 19:52   ` Andreas Gruenbacher
2021-09-03 15:52     ` Linus Torvalds
2021-09-03 18:25       ` Al Viro
2021-09-03 18:47         ` Linus Torvalds
2021-09-03 19:51       ` Andreas Grünbacher
2021-09-03 15:07 ` Filipe Manana

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