Re: [RFC PATCH v2 0/5] Add buffered write-through support to iomap & xfs

[Ojaswin Mujoo]

On Thu, Apr 23, 2026 at 02:25:43PM +0200, Pankaj Raghav (Samsung) wrote:
> > 
> > 
> > * Testing Notes (UPDATED) *
> > 
> > - I've added support for RWF_WRITETHROUGH to fsx and fsstress in
> >   xfstests and these patches survive fsx with integrity verification as
> >   well as fsstress parallel stressing.
> > - -g quick with blocks size == page size and blocksize < pagesize shows
> >   no new regressions.
> 
> I am hitting a very strange error in generic/127. I deconstructed it in
> to two commands that can reproduce the issue:
> 
> ```
> $ dd if=/dev/zero of=/media/test/fsx_lite_nommap bs=262144 count=1
> 
> $ /root/home/xfstests/ltp/fsx -l 262144 -o 65536 -S 191110531 -N 100000 -L -R -W /media/test/fsx_lite_nommap
> mapped writes DISABLED
> Seed set to 191110531
> main: filesystem does not support exchange range, disabling!
> main: atomic writes need O_DIRECT (-Z), disabling!
> short read: 0x0 bytes instead of 0x6c7f
> LOG DUMP (1 total operations):
> 1(  1 mod 256): READ     0x39381 thru 0x3ffff   (0x6c7f bytes)
> Log of operations saved to "/media/test/fsx_lite_nommap.fsxops"; replay with --replay-ops
> fsx: save_buffer: .fsxgood file too short... will save 0x0 bytes instead of 0x40000
> : Operation not supported
> Correct content saved for comparison
> (maybe hexdump "/media/test/fsx_lite_nommap" vs "/media/test/fsx_lite_nommap.fsxgood")
> ```
> 
> This is on a bs == ps (4k block size) xfs filesystem.
> ```
> $ xfs_info /media/test/
> meta-data=/dev/nvme1n1           isize=512    agcount=4, agsize=2097152 blks
>          =                       sectsz=4096  attr=2, projid32bit=1
>          =                       crc=1        finobt=1, sparse=1, rmapbt=0
>          =                       reflink=1    bigtime=1 inobtcount=1 nrext64=0
> data     =                       bsize=4096   blocks=8388608, imaxpct=25
>          =                       sunit=0      swidth=0 blks
> naming   =version 2              bsize=4096   ascii-ci=0, ftype=1
> log      =internal log           bsize=4096   blocks=16384, version=2
>          =                       sectsz=4096  sunit=1 blks, lazy-count=1
> realtime =none                   extsz=4096   blocks=0, rtextents=0
> ```
> 
> The same test passes if I pass `-G` to fsx parameters(disabling writethrough).
> 
> The error is coming when we do a read operation which feels very
> strange. Could you run this in your setup and see if you can reproduce
> them? I still do not know where the issue is coming from or it is
> because of my test setup.

Hey Pankaj, I think the xfstests branch I shared might have been missing
one small fix that can cause this issue. I've update the branch with the
fix, can you give it a try:

https://github.com/OjaswinM/xfstests/tree/iomap-buf-writethrough2

Regards,
Ojaswin

> 
> --
> Pankaj