From 5d894321c49e61379189b0ff605f316e39cbd1e9 Mon Sep 17 00:00:00 2001 From: John Garry Date: Wed, 7 May 2025 14:18:21 -0700 Subject: fs: add atomic write unit max opt to statx XFS will be able to support large atomic writes (atomic write > 1x block) in future. This will be achieved by using different operating methods, depending on the size of the write. Specifically a new method of operation based in FS atomic extent remapping will be supported in addition to the current HW offload-based method. The FS method will generally be appreciably slower performing than the HW-offload method. However the FS method will be typically able to contribute to achieving a larger atomic write unit max limit. XFS will support a hybrid mode, where HW offload method will be used when possible, i.e. HW offload is used when the length of the write is supported, and for other times FS-based atomic writes will be used. As such, there is an atomic write length at which the user may experience appreciably slower performance. Advertise this limit in a new statx field, stx_atomic_write_unit_max_opt. When zero, it means that there is no such performance boundary. Masks STATX{_ATTR}_WRITE_ATOMIC can be used to get this new field. This is ok for older kernels which don't support this new field, as they would report 0 in this field (from zeroing in cp_statx()) already. Furthermore those older kernels don't support large atomic writes - apart from block fops, but there would be consistent performance there for atomic writes in range [unit min, unit max]. Reviewed-by: Darrick J. Wong Reviewed-by: Christoph Hellwig Signed-off-by: Darrick J. Wong Acked-by: Darrick J. Wong Signed-off-by: John Garry --- include/uapi/linux/stat.h | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) (limited to 'include/uapi') diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h index f78ee3670dd5..1686861aae20 100644 --- a/include/uapi/linux/stat.h +++ b/include/uapi/linux/stat.h @@ -182,8 +182,12 @@ struct statx { /* File offset alignment for direct I/O reads */ __u32 stx_dio_read_offset_align; - /* 0xb8 */ - __u64 __spare3[9]; /* Spare space for future expansion */ + /* Optimised max atomic write unit in bytes */ + __u32 stx_atomic_write_unit_max_opt; + __u32 __spare2[1]; + + /* 0xc0 */ + __u64 __spare3[8]; /* Spare space for future expansion */ /* 0x100 */ }; -- cgit v1.2.3