Return-Path: Received: from bombadil.infradead.org ([198.137.202.9]:42642 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932290AbcFOOsC (ORCPT ); Wed, 15 Jun 2016 10:48:02 -0400 Date: Wed, 15 Jun 2016 07:48:01 -0700 From: Christoph Hellwig To: Trond Myklebust Cc: Christoph Hellwig , "linux-nfs@vger.kernel.org" , xfs@oss.sgi.com Subject: Re: [PATCH 10/12] NFS: Do not serialise O_DIRECT reads and writes Message-ID: <20160615144801.GB18524@infradead.org> References: <1465931115-30784-3-git-send-email-trond.myklebust@primarydata.com> <1465931115-30784-4-git-send-email-trond.myklebust@primarydata.com> <1465931115-30784-5-git-send-email-trond.myklebust@primarydata.com> <1465931115-30784-6-git-send-email-trond.myklebust@primarydata.com> <1465931115-30784-7-git-send-email-trond.myklebust@primarydata.com> <1465931115-30784-8-git-send-email-trond.myklebust@primarydata.com> <1465931115-30784-9-git-send-email-trond.myklebust@primarydata.com> <1465931115-30784-10-git-send-email-trond.myklebust@primarydata.com> <20160615071343.GC4318@infradead.org> <755A2A14-C6A9-4737-8335-0A6785490F6D@primarydata.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <755A2A14-C6A9-4737-8335-0A6785490F6D@primarydata.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Wed, Jun 15, 2016 at 02:29:42PM +0000, Trond Myklebust wrote: > The locking is actually simpler than XFS. It looks way more complicated. And totally undocumented. > We have 2 I/O modes: buffered I/O and direct I/O. The write lock is there to ensure safe transitions between those 2 modes, but once the mode is set, > we _only_ use shared locks in order to allow parallelism.