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

[Chuck Lever <chuck.lever@oracle.com>]

On 9/4/25 10:42 AM, Mike Snitzer wrote:
> 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?
Applied v9.

Multiple successful runs, no failures after adding "flags=direct".
Some excerpts from the last run show the server is seeing NFS
READs now:

Filesystem options:
  rw,relatime,vers=3,rsize=1048576,wsize=1048576,namlen=255,hard,
  fatal_neterrors=none,proto=rdma,port=20049,timeo=600,retrans=2,
  sec=sys,mountaddr=192.168.2.55,mountvers=3,mountproto=tcp,
  local_lock=none,addr=192.168.2.55

nfsd-1342  [004]   463.832928: nfsd_analyze_read_dio: xid=0x89784d89
fh_hash=0x024204eb offset=0 len=47008 start=0+0 middle=0+47008 end=47008+96
nfsd-1342  [004]   463.833105: nfsd_analyze_read_dio: xid=0x8a784d89
fh_hash=0x024204eb offset=47008 len=47008 start=46592+416
middle=47008+47008 end=94016+192
nfsd-1342  [004]   463.833185: nfsd_analyze_read_dio: xid=0x8b784d89
fh_hash=0x024204eb offset=94016 len=47008 start=93696+320
middle=94016+47008 end=141024+288


-- 
Chuck Lever