On Tue, Mar 18, 2025 at 9:01 AM Chuck Lever <chuck.lever@xxxxxxxxxx> wrote: > > On 3/18/25 11:09 AM, Anna Schumaker wrote: > > Hi Takeshi, > > > > On 3/18/25 11:00 AM, Takeshi Nishimura wrote: > >> Zhang Yi <yi.zhang@xxxxxxxxxx> wrote in linux-fsdevel@xxxxxxxxxxxxxxx: > >>> Add support for FALLOC_FL_WRITE_ZEROES. This first allocates blocks as > >>> unwritten, then issues a zero command outside of the running journal > >>> handle, and finally converts them to a written state. > >> > >> Picking up where the NFS4.2 WRITE_SAME discussion stalled: > >> FALLOC_FL_WRITE_ZEROES is coming, and IMO the only way to implement > >> that for NFS is via WRITE_SAME. > >> > >> How to proceed? > > > > I've been working on patches for implementing FALLOC_FL_ZERO_RANGE support > > in the NFS client using WRITE_SAME. I've also been experimenting with adding > > an ioctl for the generic pattern writing part. I'm expecting to talk about > > what I have for ioctl API at LSF next week, and I'll post an initial round > > of patches shortly after. > > > > I do still need to think through any edge cases and write tests for > > pynfs and fstests before anything can be merged. > > Takeshi, it would be immensely helpful to us if you could provide some > detail about how exactly you intend to make use of WRITE_SAME so we can > focus the development, review, and testing efforts. > > So far we don't have any specific use cases, but there is some > skepticism (as voiced in the previous thread) about whether this > facility will actually be useful. Just fyi, there has been a similar discussion in FreeBSD land. The main use case in FreeBSD land sounded like writing zeros for NVME, if I followed it. My impression is that the other patten stuff isn't very useful, since only some (a few?) SCSI devices know how to do it. The problem I see is that WRITE_SAME isn't defined in a way where the NFSv4 server can only implement zero'ng and fail the rest. As such. I am thinking that a new operation for NFSv4.2 that does writing of zeros might be preferable to trying to (mis)use WROTE_SAME. rick > > For example, do you expect to have SCSI devices that accelerate > WRITE_SAME? How will your applications use this? What kind (and size) > of patterns do you expect to need? > > > -- > Chuck Lever >
