Re: [RFC PATCH 1/2] NFSD: fix misaligned DIO READ to not use a start_extra_page, exposes rpcrdma bug?

[Mike Snitzer <snitzer@kernel.org>]

On Tue, Sep 02, 2025 at 05:27:11PM -0400, Mike Snitzer wrote:
> On Tue, Sep 02, 2025 at 05:16:10PM -0400, Chuck Lever wrote:
> > 
> > I am testing with a physically separate client and server, so I believe
> > that LOCALIO is not in play. I do see WRITEs. And other workloads (in
> > particular "fsx -Z <fname>") show READ traffic and I'm getting the
> > new trace point to fire quite a bit, and it is showing misaligned
> > READ requests. So it has something to do with dt.
> 
> OK, yeah I figured you weren't doing loopback mount, only thing that
> came to mind for you not seeing READ like expected.  I haven't had any
> problems with dt not driving READs to NFSD...
> 
> You'll certainly need to see READs in order for NFSD's new misaligned
> DIO READ handling to get tested.

I was doing some additional testing of the v9 changes last night and
realized why you weren't seeing any READs come through to NFSD:
"flags=direct" must be added to the dt commandline. Otherwise it'll
use buffered IO at the client and the READ will be serviced by the
client's page cache.

But like I said in another reply: when I just use v3 and RDMA (without
the intermediary of flexfiles at the client) I'm not able to see the
data mismatch with dt...

So while its unlikely: does adding "flags=direct" cause dt to fail
when NFSD handles the misaligned DIO READ?

Mike