From ed1128c2d0c87e5ff49c40f5529f06bc35f4251b Mon Sep 17 00:00:00 2001 From: Dave Chinner Date: Sat, 23 Jan 2021 10:06:31 -0800 Subject: [PATCH] xfs: reduce exclusive locking on unaligned dio Attempt shared locking for unaligned DIO, but only if the the underlying extent is already allocated and in written state. On failure, retry with the existing exclusive locking. Test case is fio randrw of 512 byte IOs using AIO and an iodepth of 32 IOs. Vanilla: READ: bw=4560KiB/s (4670kB/s), 4560KiB/s-4560KiB/s (4670kB/s-4670kB/s), io=134MiB (140MB), run=30001-30001msec WRITE: bw=4567KiB/s (4676kB/s), 4567KiB/s-4567KiB/s (4676kB/s-4676kB/s), io=134MiB (140MB), run=30001-30001msec Patched: READ: bw=37.6MiB/s (39.4MB/s), 37.6MiB/s-37.6MiB/s (39.4MB/s-39.4MB/s), io=1127MiB (1182MB), run=30002-30002msec WRITE: bw=37.6MiB/s (39.4MB/s), 37.6MiB/s-37.6MiB/s (39.4MB/s-39.4MB/s), io=1128MiB (1183MB), run=30002-30002msec That's an improvement from ~18k IOPS to a ~150k IOPS, which is about the IOPS limit of the VM block device setup I'm testing on. 4kB block IO comparison: READ: bw=296MiB/s (310MB/s), 296MiB/s-296MiB/s (310MB/s-310MB/s), io=8868MiB (9299MB), run=30002-30002msec WRITE: bw=296MiB/s (310MB/s), 296MiB/s-296MiB/s (310MB/s-310MB/s), io=8878MiB (9309MB), run=30002-30002msec Which is ~150k IOPS, same as what the test gets for sub-block AIO+DIO writes with this patch. Signed-off-by: Dave Chinner [hch: rebased, split unaligned from nowait] Signed-off-by: Christoph Hellwig Reviewed-by: Brian Foster Reviewed-by: Darrick J. Wong Signed-off-by: Darrick J. Wong --- fs/xfs/xfs_file.c | 58 +++++++++++++++++++++++++++++++++++----------- fs/xfs/xfs_iomap.c | 29 ++++++++++++++++------- 2 files changed, 66 insertions(+), 21 deletions(-) diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c index c60ff7b5dd82..39695b59dfcc 100644 --- a/fs/xfs/xfs_file.c +++ b/fs/xfs/xfs_file.c @@ -544,10 +544,13 @@ out_unlock: * 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. * - * This means that unaligned dio writes always block. There is no "nowait" fast - * path in this code - if IOCB_NOWAIT is set we simply return -EAGAIN up front - * and we don't have to worry about that anymore. + * 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. */ static noinline ssize_t xfs_file_dio_write_unaligned( @@ -555,13 +558,28 @@ xfs_file_dio_write_unaligned( struct kiocb *iocb, struct iov_iter *from) { - int iolock = XFS_IOLOCK_EXCL; + size_t isize = i_size_read(VFS_I(ip)); + size_t count = iov_iter_count(from); + int iolock = XFS_IOLOCK_SHARED; + unsigned int flags = IOMAP_DIO_OVERWRITE_ONLY; ssize_t ret; - /* unaligned dio always waits, bail */ - if (iocb->ki_flags & IOCB_NOWAIT) - return -EAGAIN; - xfs_ilock(ip, iolock); + /* + * 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. + */ + if (iocb->ki_pos > isize || iocb->ki_pos + count >= isize) { +retry_exclusive: + if (iocb->ki_flags & IOCB_NOWAIT) + return -EAGAIN; + iolock = XFS_IOLOCK_EXCL; + flags = IOMAP_DIO_FORCE_WAIT; + } + + ret = xfs_ilock_iocb(iocb, iolock); + if (ret) + return ret; /* * We can't properly handle unaligned direct I/O to reflink files yet, @@ -578,15 +596,29 @@ xfs_file_dio_write_unaligned( goto out_unlock; /* - * If we are doing unaligned I/O, this must be the only I/O in-flight. - * Otherwise we risk data corruption due to unwritten extent conversions - * from the AIO end_io handler. Wait for all other I/O to drain first. + * If we are doing exclusive unaligned I/O, this must be the only I/O + * in-flight. Otherwise we risk data corruption due to unwritten extent + * conversions from the AIO end_io handler. Wait for all other I/O to + * drain first. */ - inode_dio_wait(VFS_I(ip)); + if (flags & IOMAP_DIO_FORCE_WAIT) + inode_dio_wait(VFS_I(ip)); trace_xfs_file_direct_write(iocb, from); ret = iomap_dio_rw(iocb, from, &xfs_direct_write_iomap_ops, - &xfs_dio_write_ops, IOMAP_DIO_FORCE_WAIT); + &xfs_dio_write_ops, flags); + + /* + * Retry unaligned I/O with exclusive blocking semantics if the DIO + * layer rejected it for mapping or locking reasons. If we are doing + * nonblocking user I/O, propagate the error. + */ + if (ret == -EAGAIN && !(iocb->ki_flags & IOCB_NOWAIT)) { + ASSERT(flags & IOMAP_DIO_OVERWRITE_ONLY); + xfs_iunlock(ip, iolock); + goto retry_exclusive; + } + out_unlock: if (iolock) xfs_iunlock(ip, iolock); diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c index 7b9ff824e82d..ef76f775fabf 100644 --- a/fs/xfs/xfs_iomap.c +++ b/fs/xfs/xfs_iomap.c @@ -784,15 +784,28 @@ xfs_direct_write_iomap_begin( goto allocate_blocks; /* - * NOWAIT IO needs to span the entire requested IO with a single map so - * that we avoid partial IO failures due to the rest of the IO range not - * covered by this map triggering an EAGAIN condition when it is - * subsequently mapped and aborting the IO. + * NOWAIT and OVERWRITE I/O needs to span the entire requested I/O with + * a single map so that we avoid partial IO failures due to the rest of + * the I/O range not covered by this map triggering an EAGAIN condition + * when it is subsequently mapped and aborting the I/O. */ - if ((flags & IOMAP_NOWAIT) && - !imap_spans_range(&imap, offset_fsb, end_fsb)) { + if (flags & (IOMAP_NOWAIT | IOMAP_OVERWRITE_ONLY)) { error = -EAGAIN; - goto out_unlock; + if (!imap_spans_range(&imap, offset_fsb, end_fsb)) + goto out_unlock; + } + + /* + * For overwrite only I/O, we cannot convert unwritten extents without + * requiring sub-block zeroing. This can only be done under an + * exclusive IOLOCK, hence return -EAGAIN if this is not a written + * extent to tell the caller to try again. + */ + if (flags & IOMAP_OVERWRITE_ONLY) { + error = -EAGAIN; + if (imap.br_state != XFS_EXT_NORM && + ((offset | length) & mp->m_blockmask)) + goto out_unlock; } xfs_iunlock(ip, lockmode); @@ -801,7 +814,7 @@ xfs_direct_write_iomap_begin( allocate_blocks: error = -EAGAIN; - if (flags & IOMAP_NOWAIT) + if (flags & (IOMAP_NOWAIT | IOMAP_OVERWRITE_ONLY)) goto out_unlock; /* -- 2.20.1