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Date: Wed, 1 May 2024 12:36:02 +0100
From: John Garry <john.g.garry@...cle.com>
To: Dave Chinner <david@...morbit.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 01/05/2024 02:32, Dave Chinner wrote:
> 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?
Why would we? That's very restrictive. Indeed, we got to the point of
adding the sub-extent zeroing just for supporting that.
>
> .....
>> 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.
ok, fine
>
>> */
>> 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;
Do you mean xfs_extent_alignment() instead of xfs_inode_alignment()?
>
> 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.
ok, fine
>
>> +
>> + 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);
> }
ok, but again I assume you mean xfs_extent_alignment()
Thanks,
John
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