Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751896AbdI0Gkf (ORCPT ); Wed, 27 Sep 2017 02:40:35 -0400 Received: from bombadil.infradead.org ([65.50.211.133]:53264 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750817AbdI0GkI (ORCPT ); Wed, 27 Sep 2017 02:40:08 -0400 Date: Tue, 26 Sep 2017 23:40:01 -0700 From: Christoph Hellwig To: Ross Zwisler , Christoph Hellwig , Dave Chinner , Jan Kara , Andrew Morton , linux-kernel@vger.kernel.org, "Darrick J. Wong" , "J. Bruce Fields" , Dan Williams , Jeff Layton , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-nvdimm@lists.01.org, linux-xfs@vger.kernel.org Subject: Re: [PATCH 1/7] xfs: always use DAX if mount option is used Message-ID: <20170927064001.GA27601@infradead.org> References: <20170925231404.32723-1-ross.zwisler@linux.intel.com> <20170925231404.32723-2-ross.zwisler@linux.intel.com> <20170925233812.GM10955@dastard> <20170926093548.GB13627@quack2.suse.cz> <20170926110957.GR10955@dastard> <20170926143743.GB18758@lst.de> <20170926173057.GB20159@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170926173057.GB20159@linux.intel.com> User-Agent: Mutt/1.8.3 (2017-05-23) 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 Content-Length: 1442 Lines: 27 On Tue, Sep 26, 2017 at 11:30:57AM -0600, Ross Zwisler wrote: > I agree that Christoph's idea about having the system intelligently adjust to > use DAX based on performance information it gathers about the underlying > persistent memory (probably via the HMAT on x86_64 systems) is interesting, > but I think we're still a ways away from that. So what are the missing blockers for a getting started? > FWIW, as my patches suggest and Jan observed I think that we should allow > users to turn on DAX by treating the inode flag and the mount flag as an 'or' > operation. i.e. you get DAX if either the mount option is specified or if the > inode flag is set, and you can continue to manipulate the per-inode flag as > you want regardless of the mount option. I think this provides maximum > flexibility of the mechanism to select DAX without enforcing policy. IFF we stick to the dax flag that's the only workable way. The only major issue I still see with that is that this allows unprivilegued users to enable DAX on a any file they own / have write access to. So there isn't really any way to effectively disable the DAX path by the sysadmin. > Does it make sense at this point to just start a "dax" man page that can > contain info about the mount options, inode flags, kernel config options, how > to get PMDs, etc? Or does this documentation need to be sprinkled around more > in existing man pages? A dax manpage would be good.