Hi John, On Thu, Jun 19, 2025 at 03:44:55PM +0000, John Garry wrote: > XFS supports atomic writes - or untorn writes - based on two different > methods: > - HW offload in the disk > - FS method based on out-of-place writes > > The value reported in stx_atomic_write_unit_max will be the max size of the > FS-based method. > > The max atomic write unit size of the FS-based atomic writes will > typically be much larger than what is capable from the HW offload. However, > FS-based atomic writes will also be typically much slower. > > Advertise this HW offload size limit to the user in a new statx member, > stx_atomic_write_unit_max_opt. > > We want STATX_WRITE_ATOMIC to get this new member in addition to the > already-existing members, so mention that a value of 0 in > stx_atomic_write_unit_max_opt means that stx_atomic_write_unit_max holds > this optimised limit. > > Linux will zero unused statx members, so stx_atomic_write_unit_max_opt > will always hold 0 for older kernel versions which do not support > this FS-based atomic write method (for XFS). > > Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx> Thanks! Patch applied. <https://www.alejandro-colomar.es/src/alx/linux/man-pages/man-pages.git/commit/?h=contrib&id=6dd3ceed42a94815ae41f0a7ec2e946a12a8f4be> Cheers, Alex > --- > man/man2/statx.2 | 21 ++++++++++++++++++++- > 1 file changed, 20 insertions(+), 1 deletion(-) > > diff --git a/man/man2/statx.2 b/man/man2/statx.2 > index 273d80711..07ac60b3c 100644 > --- a/man/man2/statx.2 > +++ b/man/man2/statx.2 > @@ -74,6 +74,9 @@ struct statx { > \& > /* File offset alignment for direct I/O reads */ > __u32 stx_dio_read_offset_align; > +\& > + /* Direct I/O atomic write max opt limit */ > + __u32 stx_atomic_write_unit_max_opt; > }; > .EE > .in > @@ -266,7 +269,8 @@ STATX_SUBVOL Want stx_subvol > (since Linux 6.10; support varies by filesystem) > STATX_WRITE_ATOMIC Want stx_atomic_write_unit_min, > stx_atomic_write_unit_max, > - and stx_atomic_write_segments_max. > + stx_atomic_write_segments_max, > + and stx_atomic_write_unit_max_opt. > (since Linux 6.11; support varies by filesystem) > STATX_DIO_READ_ALIGN Want stx_dio_read_offset_align. > (since Linux 6.14; support varies by filesystem) > @@ -514,6 +518,21 @@ is supported on block devices since Linux 6.11. > The support on regular files varies by filesystem; > it is supported by xfs and ext4 since Linux 6.13. > .TP > +.I stx_atomic_write_unit_max_opt > +The maximum size (in bytes) which is > +optimised for writes issued with torn-write protection. > +If non-zero, > +this value will not exceed the value in > +.I stx_atomic_write_unit_max > +and will not be less than the value in > +.IR stx_atomic_write_unit_min . > +A value of zero indicates that > +.I stx_atomic_write_unit_max > +is the optimised limit. > +Slower writes may be experienced when the size of the write exceeds > +.I stx_atomic_write_unit_max_opt > +(when non-zero). > +.TP > .I stx_atomic_write_segments_max > The maximum number of elements in an array of vectors > for a write with torn-write protection enabled. > -- > 2.31.1 > -- <https://www.alejandro-colomar.es/>
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