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

[Ojaswin Mujoo]

On Fri, Apr 17, 2026 at 05:54:46AM +0200, Pankaj Raghav (Samsung) wrote:
> Thanks for the patches.
> 
> > The implementation of write-through combines the buffered IO frontend
> > with dio backend, which leads to some interesting interactions.
> > I've added most of the design notes in respective patches. Please note
> > that this is an initial RFC to iron out any early design issues. This is
> > largely based on suggestions from Dave an Jan in [1] so thanks for the
> > pointers!
> > 
> > 
> > * 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.
> 
> Could you point me to your xfstests repo where you have added this
> support? :)
> I have been traveling the whole week. I can give the patches a spin in
> my setup in the coming days.

Hi Pankaj, you can find the xfstests support here:

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

For fsstress, I was using generic/013 modified to run more operations.
For fsx, any of the run_fsx stressing tests would do, or you could use
the following command (writethrough should auto enable if kernel
supports it):

/home/ojas/workspace/xfstests-dev/ltp/fsx \
 -N 100000 \
 -o 65536 \
 -l 500000 \
 -r 4096 \
 -t 512 \
 -w 512 \
 --record-ops=rwf_rt.fsxops \
 $MNT/junk

Regards,
Ojaswin

> 
> > - -g quick with blocks size == page size and blocksize < pagesize shows
> >   no new regressions.
> > 
> > 
> > * Design TODOs (UPDATED) *
> > 
> > - Evaluate if we need to tag page cache dirty bit in xarray, since 
> >   PG_Writeback is already set on the folio.
> > - Look into a better way to refactor writethrough path by reusing common
> >   parts of dio code.
> >