On Fri, Sep 18, 2009 at 5:12 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > On Fri, Sep 18, 2009 at 12:47:57PM -0400, William A. (Andy) Adamson wrote: >> 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. > > Right. I think you're agreeing with me? yes! > >> 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. > > Yes. For the additional space, shall we use what this patch calculates or some other metric? > >> > 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). > > Right. The difference is that now it looks to me like we're actually > going to start promising that we support the large request + large > response case, when actually we don't. OK - I see your point. With MAXREAD or MAXWRITE we only promise either a large request or a large response per compound, not a large request and a large response in a single compound, e.g. a read and a write in the same compound. > > I guess the problem's unlikely to arise, so maybe it's not worth fixing. > But it's annoying to have yet another undocumented restriction on the > compounds we'll accept. I wonder what other servers are doing. -->Andy > > --b. > -- 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
