On Tue, Sep 04 2018, Trond Myklebust wrote: > On Wed, 2018-09-05 at 08:47 +1000, NeilBrown wrote: >> With NFSv4.1, the server specifies max_rqst_sz and max_resp_sz in the >> reply to CREATE session. >> >> If the client finds it needs to call nfs4_reset_session(), it might >> get >> smaller sizes back, so any pending read/writes would need to be >> resized. >> >> However, I cannot see how the retry handling for reads/writes has any >> chance to change the size. It looks like a request is broken up to >> match the original ->rsize and ->wsize, then those individual IO >> requests can be retried, but the higher level request is never >> re-evaluated in light of a new size. >> >> Am I missing something, or is this not supported at present? >> If it isn't supported, any suggestions on how best to handle a >> reduction of the rsize/wsize ?? >> > > Why would a sane server want to do this? Why would a sane protocol support it? :-) I have a network trace of SLE11-SP4 (3.0 based) talking to "a NetApp appliance". It sends a 64K write and gets NFS4ERR_REQ_TOO_BIG. It then closes the file (getting NFS4ERR_SEQ_MISORDERED even though it used a seq number 1 more than the WRITE request), and then DESTROY_SESSION and CREATE_SESSION. The CREATE_SESSION gets "max req size" of 33812 and "max resp size" of 33672. It then opens the file again and retries the 64K write.... I have a separate trace showing the initial mount where the sizes are 71680 and 81920. I don't have a trace where it stops working, but reportedly writes work smoothly for some hours after a mount, but then suddenly stop working. The CREATE_SESSION *call* requests I see have the small (32K) sizes, but presumably they are the result of a previous CREATE_SESSION reply giving a small value. I just had a thought. If one session is shared by two "struct nfs_server" with different ->rsize or ->wsize, then the session might get set up with the smaller size, and the mount using the larger size will get confused. In 3.0 (and even 3.10) nfs4_init_session() limits the requested session parameters to ->rsize and ->wsize. That changed in 18aad3d552c7. Maybe I just need to remove that code from nfs4_init_session(). I'll give it a try. Thanks, NeilBrown
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