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Message-ID: <ZjGbkAuGj0MhXAZ/@dread.disaster.area>
Date: Wed, 1 May 2024 11:32:00 +1000
From: Dave Chinner <david@...morbit.com>
To: John Garry <john.g.garry@...cle.com>
Cc: djwong@...nel.org, hch@....de, viro@...iv.linux.org.uk,
brauner@...nel.org, jack@...e.cz, chandan.babu@...cle.com,
willy@...radead.org, axboe@...nel.dk, martin.petersen@...cle.com,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
tytso@....edu, jbongio@...gle.com, ojaswin@...ux.ibm.com,
ritesh.list@...il.com, mcgrof@...nel.org, p.raghav@...sung.com,
linux-xfs@...r.kernel.org, catherine.hoang@...cle.com
Subject: Re: [PATCH v3 15/21] fs: xfs: iomap: Sub-extent zeroing
On Mon, Apr 29, 2024 at 05:47:40PM +0000, John Garry wrote:
> Set iomap->extent_size when sub-extent zeroing is required.
>
> We treat a sub-extent write same as an unaligned write, so we can leverage
> the existing sub-FSblock unaligned write support, i.e. try a shared lock
> with IOMAP_DIO_OVERWRITE_ONLY flag, if this fails then try the exclusive
> lock.
>
> In xfs_iomap_write_unwritten(), FSB calcs are now based on the extsize.
If forcedalign is set, should we just reject unaligned DIOs?
....
> Signed-off-by: John Garry <john.g.garry@...cle.com>
> ---
> fs/xfs/xfs_file.c | 35 ++++++++++++++++++++++-------------
> fs/xfs/xfs_iomap.c | 13 +++++++++++--
> 2 files changed, 33 insertions(+), 15 deletions(-)
>
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index e81e01e6b22b..ee4f94cf6f4e 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -620,18 +620,19 @@ xfs_file_dio_write_aligned(
> * Handle block unaligned direct I/O writes
* Handle unaligned direct IO writes.
> *
> * In most cases direct I/O writes will be done holding IOLOCK_SHARED, allowing
> - * them to be done in parallel with reads and other direct I/O writes. However,
> - * if the I/O is not aligned to filesystem blocks, the direct I/O layer may need
> - * to do sub-block zeroing and that requires serialisation against other direct
> - * I/O to the same block. In this case we need to serialise the submission of
> - * the unaligned I/O so that we don't get racing block zeroing in the dio layer.
> - * In the case where sub-block zeroing is not required, we can do concurrent
> - * sub-block dios to the same block successfully.
> + * them to be done in parallel with reads and other direct I/O writes.
> + * However if the I/O is not aligned to filesystem blocks/extent, the direct
> + * I/O layer may need to do sub-block/extent zeroing and that requires
> + * serialisation against other direct I/O to the same block/extent. In this
> + * case we need to serialise the submission of the unaligned I/O so that we
> + * don't get racing block/extent zeroing in the dio layer.
> + * In the case where sub-block/extent zeroing is not required, we can do
> + * concurrent sub-block/extent dios to the same block/extent successfully.
> *
> * Optimistically submit the I/O using the shared lock first, but use the
> * IOMAP_DIO_OVERWRITE_ONLY flag to tell the lower layers to return -EAGAIN
> - * if block allocation or partial block zeroing would be required. In that case
> - * we try again with the exclusive lock.
> + * if block/extent allocation or partial block/extent zeroing would be
> + * required. In that case we try again with the exclusive lock.
Rather than changing every "block" to "block/extent", leave the bulk
of the comment unchanged and add another paragraph to it that says
something like:
* If forced extent alignment is turned on, then serialisation
* constraints are extended from filesystem block alignment
* to extent alignment boundaries. In this case, we treat any
* non-extent-aligned DIO the same as a sub-block DIO.
> */
> static noinline ssize_t
> xfs_file_dio_write_unaligned(
> @@ -646,9 +647,9 @@ xfs_file_dio_write_unaligned(
> ssize_t ret;
>
> /*
> - * Extending writes need exclusivity because of the sub-block zeroing
> - * that the DIO code always does for partial tail blocks beyond EOF, so
> - * don't even bother trying the fast path in this case.
> + * Extending writes need exclusivity because of the sub-block/extent
> + * zeroing that the DIO code always does for partial tail blocks
> + * beyond EOF, so don't even bother trying the fast path in this case.
> */
> if (iocb->ki_pos > isize || iocb->ki_pos + count >= isize) {
> if (iocb->ki_flags & IOCB_NOWAIT)
> @@ -714,11 +715,19 @@ xfs_file_dio_write(
> struct xfs_inode *ip = XFS_I(file_inode(iocb->ki_filp));
> struct xfs_buftarg *target = xfs_inode_buftarg(ip);
> size_t count = iov_iter_count(from);
> + struct xfs_mount *mp = ip->i_mount;
> + unsigned int blockmask;
>
> /* direct I/O must be aligned to device logical sector size */
> if ((iocb->ki_pos | count) & target->bt_logical_sectormask)
> return -EINVAL;
> - if ((iocb->ki_pos | count) & ip->i_mount->m_blockmask)
> +
> + if (xfs_inode_has_forcealign(ip) && ip->i_extsize > 1)
> + blockmask = XFS_FSB_TO_B(mp, ip->i_extsize) - 1;
> + else
> + blockmask = mp->m_blockmask;
alignmask = XFS_FSB_TO_B(mp, xfs_inode_alignment(ip)) - 1;
Note that this would consider sub rt_extsize IO as unaligned, which
may be undesirable. In that case, we should define a second helper
such as xfs_inode_io_alignment() that doesn't take into account RT
extent sizes because we can still do filesystem block sized
unwritten extent conversion on those devices. The same IO-specific
wrapper would be used for the other cases in this patch, too.
> +
> + if ((iocb->ki_pos | count) & blockmask)
> return xfs_file_dio_write_unaligned(ip, iocb, from);
> return xfs_file_dio_write_aligned(ip, iocb, from);
> }
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index 4087af7f3c9f..1a3692bbc84d 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -138,6 +138,8 @@ xfs_bmbt_to_iomap(
>
> iomap->validity_cookie = sequence_cookie;
> iomap->folio_ops = &xfs_iomap_folio_ops;
> + if (xfs_inode_has_forcealign(ip) && ip->i_extsize > 1)
> + iomap->extent_size = XFS_FSB_TO_B(mp, ip->i_extsize);
iomap->io_block_size = XFS_FSB_TO_B(mp, xfs_inode_alignment(ip));
> return 0;
> }
>
> @@ -570,8 +572,15 @@ xfs_iomap_write_unwritten(
>
> trace_xfs_unwritten_convert(ip, offset, count);
>
> - offset_fsb = XFS_B_TO_FSBT(mp, offset);
> - count_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + count);
> + if (xfs_inode_has_forcealign(ip) && ip->i_extsize > 1) {
> + xfs_extlen_t extsize_bytes = mp->m_sb.sb_blocksize * ip->i_extsize;
> +
> + offset_fsb = XFS_B_TO_FSBT(mp, round_down(offset, extsize_bytes));
> + count_fsb = XFS_B_TO_FSB(mp, round_up(offset + count, extsize_bytes));
> + } else {
> + offset_fsb = XFS_B_TO_FSBT(mp, offset);
> + count_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + count);
> + }
More places we can use a xfs_inode_alignment() helper.
offset_fsb = XFS_B_TO_FSBT(mp, offset);
count_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + count);
rounding = XFS_FSB_TO_B(mp, xfs_inode_alignment(ip));
if (rounding > 1) {
offset_fsb = rounddown_64(offset_fsb, rounding);
count_fsb = roundup_64(count_fsb, rounding);
}
Cheers,
Dave.
--
Dave Chinner
david@...morbit.com
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