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Wong" To: John Garry Cc: brauner@kernel.org, cem@kernel.org, dchinner@redhat.com, hch@lst.de, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, ojaswin@linux.ibm.com, ritesh.list@gmail.com, martin.petersen@oracle.com Subject: Re: [PATCH RFC 07/10] xfs: Add xfs_file_dio_write_atomic() Message-ID: <20250205195540.GY21808@frogsfrogsfrogs> References: <20250204120127.2396727-1-john.g.garry@oracle.com> <20250204120127.2396727-8-john.g.garry@oracle.com> Precedence: bulk X-Mailing-List: linux-xfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250204120127.2396727-8-john.g.garry@oracle.com> On Tue, Feb 04, 2025 at 12:01:24PM +0000, John Garry wrote: > Add xfs_file_dio_write_atomic() for dedicated handling of atomic writes. > > In case of -EAGAIN being returned from iomap_dio_rw(), reissue the write > in CoW-based atomic write mode. > > In the CoW-based atomic write mode, first unshare blocks so that we don't > have a cow fork for the data in the range which we are writing. > > Signed-off-by: John Garry > --- > fs/xfs/xfs_file.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 51 insertions(+) > > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c > index fd05b66aea3f..12af5cdc3094 100644 > --- a/fs/xfs/xfs_file.c > +++ b/fs/xfs/xfs_file.c > @@ -619,6 +619,55 @@ xfs_file_dio_write_aligned( > return ret; > } > > +static noinline ssize_t > +xfs_file_dio_write_atomic( > + struct xfs_inode *ip, > + struct kiocb *iocb, > + struct iov_iter *from) > +{ > + unsigned int iolock = XFS_IOLOCK_SHARED; > + bool use_cow = false; > + unsigned int dio_flags; > + ssize_t ret; > + > +retry: > + ret = xfs_ilock_iocb_for_write(iocb, &iolock); > + if (ret) > + return ret; > + > + ret = xfs_file_write_checks(iocb, from, &iolock); > + if (ret) > + goto out_unlock; > + > + if (use_cow) { > + ret = xfs_reflink_unshare(ip, iocb->ki_pos, > + iov_iter_count(from)); Nit: continuation lines should be indented two tabs: ret = xfs_reflink_unshare(ip, iocb->ki_pos, iov_iter_count(from)); > + if (ret) > + goto out_unlock; > + } > + > + trace_xfs_file_direct_write(iocb, from); > + if (use_cow) > + dio_flags = IOMAP_DIO_ATOMIC_COW; > + else > + dio_flags = 0; I also think you could eliminate use_cow by initializing dio_flags to zero at the top, OR'ing in IOMAP_DIO_ATOMIC_COW in the retry clause below, and using (dio_flags & IOMAP_DIO_ATOMIC_COW) to determine if you should call unshare above. Note: This serializes all the software untorn direct writes. I think a more performant solution would allocate the cow staging blocks ondisk, attach them to the directio ioend context, and alter ->iomap_begin and the ioend remap to use the attached blocks, but that's a lot more surgery. --D > + > + ret = iomap_dio_rw(iocb, from, &xfs_direct_write_iomap_ops, > + &xfs_dio_write_ops, dio_flags, NULL, 0); > + > + if (ret == -EAGAIN && !(iocb->ki_flags & IOCB_NOWAIT) && !use_cow) { > + xfs_iunlock(ip, iolock); > + iolock = XFS_IOLOCK_EXCL; > + use_cow = true; > + goto retry; > + } > + > +out_unlock: > + if (iolock) > + xfs_iunlock(ip, iolock); > + return ret; > +} > + > /* > * Handle block unaligned direct I/O writes > * > @@ -723,6 +772,8 @@ xfs_file_dio_write( > return -EINVAL; > if ((iocb->ki_pos | count) & ip->i_mount->m_blockmask) > return xfs_file_dio_write_unaligned(ip, iocb, from); > + if (iocb->ki_flags & IOCB_ATOMIC) > + return xfs_file_dio_write_atomic(ip, iocb, from); > return xfs_file_dio_write_aligned(ip, iocb, from); > } > > -- > 2.31.1 > >