From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from relay.sgi.com (relay2.corp.sgi.com [137.38.102.29]) by oss.sgi.com (Postfix) with ESMTP id B711A7CA1 for ; Thu, 5 May 2016 10:22:34 -0500 (CDT) Received: from cuda.sgi.com (cuda1.sgi.com [192.48.157.11]) by relay2.corp.sgi.com (Postfix) with ESMTP id 548F5304051 for ; Thu, 5 May 2016 08:22:34 -0700 (PDT) Received: from bombadil.infradead.org ([198.137.202.9]) by cuda.sgi.com with ESMTP id 8KlyXySbHUTjjaqd (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NO) for ; Thu, 05 May 2016 08:22:32 -0700 (PDT) Date: Thu, 5 May 2016 08:22:30 -0700 From: Christoph Hellwig Subject: Re: [PATCH v4 5/7] fs: prioritize and separate direct_io from dax_io Message-ID: <20160505152230.GA3994@infradead.org> References: <1461878218-3844-1-git-send-email-vishal.l.verma@intel.com> <1461878218-3844-6-git-send-email-vishal.l.verma@intel.com> <5727753F.6090104@plexistor.com> <20160505142433.GA4557@infradead.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: xfs-bounces@oss.sgi.com Sender: xfs-bounces@oss.sgi.com To: Dan Williams Cc: Boaz Harrosh , Jan Kara , Matthew Wilcox , Jens Axboe , linux-nvdimm , "linux-kernel@vger.kernel.org" , XFS Developers , Christoph Hellwig , Linux MM , linux-block@vger.kernel.org, Al Viro , linux-fsdevel , Andrew Morton , linux-ext4 On Thu, May 05, 2016 at 08:15:32AM -0700, Dan Williams wrote: > > Agreed - makig O_DIRECT less direct than not having it is plain stupid, > > and I somehow missed this initially. > > Of course I disagree because like Dave argues in the msync case we > should do the correct thing first and make it fast later, but also > like Dave this arguing in circles is getting tiresome. We should do the right thing first, and make it fast later. But this proposal is not getting it right - it still does not handle errors for the fast path, but magically makes it work for direct I/O by in general using a less optional path for O_DIRECT. It's getting the worst of all choices. As far as I can tell the only sensible option is to: - always try dax-like I/O first - have a custom get_user_pages + rw_bytes fallback handles bad blocks when hitting EIO And then we need to sort out the concurrent write synchronization. Again there I think we absolutely have to obey Posix for the !O_DIRECT case and can avoid it for O_DIRECT, similar to the existing non-DAX semantics. If we want any special additional semantics we _will_ need a special O_DAX flag. _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs