On Mon, Sep 14, 2009 at 3:03 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > On Fri, Sep 11, 2009 at 06:52:55PM -0400, andros@xxxxxxxxxx wrote: >> From: Andy Adamson <andros@xxxxxxxxxx> >> >> Both the max request and the max response size include the RPC header with >> credential (request only) and verifier as well as the payload. >> >> The RPCSEC_GSS credential and verifier are the largest. Kerberos is the only >> supported GSS security mechansim, so the Kerberos GSS credential and verifier >> sizes are used. > > Rather than trying to estimate this is might be simplest just to use > what the server's using to allocate memory: RPCSVC_MAXPAGES. No, that > also takes into account space for the reply. You could do > > PAGE_SIZE * (1 + (RPCSVC_MAXPAYLOAD+PAGE_SIZE-1)/PAGE_SIZE) > > Actually, by design the server's real limit is actually on the sum of > the request and the reply sizes. I think the actual limit is svc_max_payload rounded up to a multiple of PAGE_SIZE plus PAGE_SIZE. which is a lot smaller than the sum of the request and reply sizes. See below. Note that svc_max_payload is what is returned in nfs4_encode_fattr for MAXREAD and for MAXWRITE. These attributes use svc_max_payload in the same way this patch does - the maximum data size not including rpc headers. I don't think the server wants is to advertise a MAXREAD/WRITE that it can't supply because the fore channel maxrequest/maxresponse is too small, so some additional space needs to be added to svc_max_payload for the fore channel. > > What happens if we get a request such that both the request and reply > are under our advertised limits, but the sum is too much? Can we just > declare that no client will be that weird and that we shouldn't have to > worry about it? I think the server already has this problem. In svc_init_buffer which sets up the pages for a server thread request/response handling, it uses sv_max_mesg / PAGE_SIZE + 1 with the comment "extra page as we hold both request and reply. We assume one is at most one page" where sv_max_mesg = roundup(serv->sv_max_payload + PAGE_SIZE, PAGE_SIZE). -->Andy > > --b. > _______________________________________________ > pNFS mailing list > pNFS@xxxxxxxxxxxxx > http://linux-nfs.org/cgi-bin/mailman/listinfo/pnfs > -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
