Return-Path: linux-nfs-owner@vger.kernel.org Received: from bombadil.infradead.org ([198.137.202.9]:58596 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757337AbbBEL1y (ORCPT ); Thu, 5 Feb 2015 06:27:54 -0500 Date: Thu, 5 Feb 2015 03:27:49 -0800 From: Christoph Hellwig To: Trond Myklebust Cc: linux-nfs@vger.kernel.org, Olga.Kornievskaia@netapp.com Subject: Re: [PATCH 1/2] NFSv4.1: Ask for no delegation on OPEN if using O_DIRECT Message-ID: <20150205112749.GA13486@infradead.org> References: <1423000784-93180-1-git-send-email-trond.myklebust@primarydata.com> <20150204081624.GA16543@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: Sender: linux-nfs-owner@vger.kernel.org List-ID: On Wed, Feb 04, 2015 at 07:32:43AM -0500, Trond Myklebust wrote: > Delegations are all about allowing the NFS client to cache data > aggressively, and notifying when it is no longer safe to do so. That > is clearly not of interest to an application using O_DIRECT, since it > is by definition managing the data cache (if there is one) instead of > the NFS client. We don't share delegation state with userspace and > even if we did, there are no existing applications out there that are > capable (or even interested) of taking advantage of it. > > You can argue that the client could still use the delegation to cache > metadata and open/lock state, but most of the users of O_DIRECT of > which I'm aware tend to be data intensive, and not very metadata/state > intensive. So why burden both the server and the with that extra state > management? How does the delegation hurt us in this case? That needs to go into the patch description, and into a comment near the code.