From 7422bbd030210fbdc011acfd6f0f15b966fd2b46 Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Thu, 9 Jan 2025 09:31:04 +0100 Subject: [PATCH] xfs: report the correct read/write dio alignment for reflinked inodes For I/O to reflinked blocks we always need to write an entire new file system block, and the code enforces the file system block alignment for the entire file if it has any reflinked blocks. Use the new STATX_DIO_READ_ALIGN flag to report the asymmetric read vs write alignments for reflinked files. Signed-off-by: Christoph Hellwig Link: https://lore.kernel.org/r/20250109083109.1441561-5-hch@lst.de Reviewed-by: John Garry Reviewed-by: Darrick J. Wong Signed-off-by: Christian Brauner --- fs/xfs/xfs_iops.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-) diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c index 6b0228a21617..40289fe6f5b2 100644 --- a/fs/xfs/xfs_iops.c +++ b/fs/xfs/xfs_iops.c @@ -580,9 +580,24 @@ xfs_report_dioalign( struct xfs_buftarg *target = xfs_inode_buftarg(ip); struct block_device *bdev = target->bt_bdev; - stat->result_mask |= STATX_DIOALIGN; + stat->result_mask |= STATX_DIOALIGN | STATX_DIO_READ_ALIGN; stat->dio_mem_align = bdev_dma_alignment(bdev) + 1; - stat->dio_offset_align = bdev_logical_block_size(bdev); + + /* + * For COW inodes, we can only perform out of place writes of entire + * allocation units (blocks or RT extents). + * For writes smaller than the allocation unit, we must fall back to + * buffered I/O to perform read-modify-write cycles. At best this is + * highly inefficient; at worst it leads to page cache invalidation + * races. Tell applications to avoid this by reporting the larger write + * alignment in dio_offset_align, and the smaller read alignment in + * dio_read_offset_align. + */ + stat->dio_read_offset_align = bdev_logical_block_size(bdev); + if (xfs_is_cow_inode(ip)) + stat->dio_offset_align = xfs_inode_alloc_unitsize(ip); + else + stat->dio_offset_align = stat->dio_read_offset_align; } static void @@ -658,7 +673,7 @@ xfs_vn_getattr( stat->rdev = inode->i_rdev; break; case S_IFREG: - if (request_mask & STATX_DIOALIGN) + if (request_mask & (STATX_DIOALIGN | STATX_DIO_READ_ALIGN)) xfs_report_dioalign(ip, stat); if (request_mask & STATX_WRITE_ATOMIC) xfs_report_atomic_write(ip, stat);