From: "William A. (Andy) Adamson" Subject: Re: [pnfs] [PATCH 2/2] nfsd41: add RPC header size to fore channel negotiation Date: Fri, 18 Sep 2009 12:47:57 -0400 Message-ID: <89c397150909180947w69b0139dx732100109e2793b0@mail.gmail.com> References: <1252709575-3426-1-git-send-email-andros@netapp.com> <1252709575-3426-2-git-send-email-andros@netapp.com> <1252709575-3426-3-git-send-email-andros@netapp.com> <20090914190315.GD1658@fieldses.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: linux-nfs@vger.kernel.org, pnfs@linux-nfs.org To: "J. Bruce Fields" Return-path: Received: from mail-yw0-f175.google.com ([209.85.211.175]:55904 "EHLO mail-yw0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755648AbZIRQrx convert rfc822-to-8bit (ORCPT ); Fri, 18 Sep 2009 12:47:53 -0400 Received: by ywh5 with SMTP id 5so1422981ywh.4 for ; Fri, 18 Sep 2009 09:47:57 -0700 (PDT) In-Reply-To: <20090914190315.GD1658@fieldses.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Mon, Sep 14, 2009 at 3:03 PM, J. Bruce Fields = wrote: > On Fri, Sep 11, 2009 at 06:52:55PM -0400, andros@netapp.com wrote: >> From: Andy Adamson >> >> Both the max request and the max response size include the RPC heade= r with >> credential (request only) =A0and 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. =A0No, t= hat > also takes into account space for the reply. =A0You could do > > =A0 =A0 =A0 =A0PAGE_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? =A0Can we j= ust > 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 =3D roundup(serv->sv_max_payload + PAGE_SIZE, PAGE_SIZE). -->Andy > > --b. > _______________________________________________ > pNFS mailing list > pNFS@linux-nfs.org > http://linux-nfs.org/cgi-bin/mailman/listinfo/pnfs >