Return-Path: Received: from fieldses.org ([174.143.236.118]:36853 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752197Ab0JASPN (ORCPT ); Fri, 1 Oct 2010 14:15:13 -0400 Date: Fri, 1 Oct 2010 14:14:56 -0400 From: "J. Bruce Fields" To: Marc Eshel Cc: Benny Halevy , Boaz Harrosh , Tigran Mkrtchyan , NFS list , linux-nfs-owner@vger.kernel.org, Fred Isaman Subject: Re: pNFS DS session Message-ID: <20101001181455.GC32256@fieldses.org> References: <4CA44AAA.4030803@panasas.com> <4CA45462.1070503@desy.de> <4CA455C4.4030705@panasas.com> <4CA57BC6.9030701@desy.de> <4CA5A012.2090404@panasas.com> <4CA5D537.30300@panasas.com> <4CA600F4.2010006@almaden.ibm.com> <20101001171012.GB30570@fieldses.org> <4CA621A4.2040508@almaden.ibm.com> Content-Type: text/plain; charset=us-ascii In-Reply-To: <4CA621A4.2040508@almaden.ibm.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: MIME-Version: 1.0 On Fri, Oct 01, 2010 at 11:00:04AM -0700, Marc Eshel wrote: > On 10/1/2010 10:10 AM, J. Bruce Fields wrote: > >On Fri, Oct 01, 2010 at 08:40:36AM -0700, Marc Eshel wrote: > >> On 10/1/2010 5:33 AM, Benny Halevy wrote: > >>>On 2010-10-01 10:47, Boaz Harrosh wrote: > >>>>On 10/01/2010 08:12 AM, Tigran Mkrtchyan wrote: > >>>>> On 10/01/2010 06:17 AM, Marc Eshel wrote: > >>>>>>Hi Benny, > >>>>>> > >>>>>>Running connectathon I see that some times the clients decides to destroy > >>>>>>the session with the DS. The test continue and the session is > >>>>>>re-established. It looks like layout return reduces the hold on device > >>>>>>info the reduces the hold on the client struct which decide to destroy the > >>>>>>session. Is that a known problem? > >>>>>> > >>>>Yes, I want to emphasize on Marks words: "a known *problem*" > >>>Marc, assuming the code behaves as expected, does this cause any other badness > >>>like the GETATTRs you see going out to the DS? > >>> > >>>Benny > >>> > >>No i don't see any "badness" the test continues without errors and > >>this problem is not related to the GETATTRs I see on the DS but I > >>would consider destroying the session in short run of couple of > >>minutes some times more than one time as something bad. > >Why? > > > >I wouldn't expect session destruction/creation to be *that* expensive. > > I assumed that it is inexpensive. We are talking about potential > destruction/creation of session from every DS for each file IO if > there is no overlap in holding layouts, right ? Well, I guess the tradeoffs aren't obvious to me: if you end up having to set up an enormous number of sessions (and tcp connections, etc.) all at once, then I can see why it might be a problem. It would also seem inefficient to keep around an enormous number of those when they aren't being used for a while. --b.