From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757073AbcEEOYj (ORCPT ); Thu, 5 May 2016 10:24:39 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:52520 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751270AbcEEOYg (ORCPT ); Thu, 5 May 2016 10:24:36 -0400 Date: Thu, 5 May 2016 07:24:33 -0700 From: Christoph Hellwig To: Boaz Harrosh Cc: Vishal Verma , linux-nvdimm@ml01.01.org, Jens Axboe , Jan Kara , Andrew Morton , Matthew Wilcox , Dave Chinner , linux-kernel@vger.kernel.org, xfs@oss.sgi.com, linux-block@vger.kernel.org, linux-mm@kvack.org, Al Viro , Christoph Hellwig , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org Subject: Re: [PATCH v4 5/7] fs: prioritize and separate direct_io from dax_io Message-ID: <20160505142433.GA4557@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5727753F.6090104@plexistor.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 02, 2016 at 06:41:51PM +0300, Boaz Harrosh wrote: > > All IO in a dax filesystem used to go through dax_do_io, which cannot > > handle media errors, and thus cannot provide a recovery path that can > > send a write through the driver to clear errors. > > > > Add a new iocb flag for DAX, and set it only for DAX mounts. In the IO > > path for DAX filesystems, use the same direct_IO path for both DAX and > > direct_io iocbs, but use the flags to identify when we are in O_DIRECT > > mode vs non O_DIRECT with DAX, and for O_DIRECT, use the conventional > > direct_IO path instead of DAX. > > > > Really? What are your thinking here? > > What about all the current users of O_DIRECT, you have just made them > 4 times slower and "less concurrent*" then "buffred io" users. Since > direct_IO path will queue an IO request and all. > (And if it is not so slow then why do we need dax_do_io at all? [Rhetorical]) > > I hate it that you overload the semantics of a known and expected > O_DIRECT flag, for special pmem quirks. This is an incompatible > and unrelated overload of the semantics of O_DIRECT. Agreed - makig O_DIRECT less direct than not having it is plain stupid, and I somehow missed this initially. This whole DAX story turns into a major nightmare, and I fear all our hodge podge tweaks to the semantics aren't helping it. It seems like we simply need an explicit O_DAX for the read/write bypass if can't sort out the semantics (error, writer synchronization) just as we need a special flag for MMAP..