Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751517AbdGZULj (ORCPT ); Wed, 26 Jul 2017 16:11:39 -0400 Received: from bombadil.infradead.org ([65.50.211.133]:41169 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751011AbdGZULh (ORCPT ); Wed, 26 Jul 2017 16:11:37 -0400 Date: Wed, 26 Jul 2017 13:11:36 -0700 From: Christoph Hellwig To: Dan Williams Cc: Christoph Hellwig , "linux-nvdimm@lists.01.org" , Linux Kernel Mailing List , linux-f2fs-devel@lists.sourceforge.net, linux-fsdevel , Jaegeuk Kim , sunqiuyang Subject: Re: [PATCH v8 1/1] f2fs: dax: implement direct access Message-ID: <20170726201136.GA30039@infradead.org> References: <1500552639-18523-1-git-send-email-sunqiuyang@huawei.com> <20170726072634.GA4684@infradead.org> <20170726170147.GA31930@infradead.org> <20170726172011.GA30142@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.8.0 (2017-02-23) 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: 857 Lines: 22 On Wed, Jul 26, 2017 at 12:16:11PM -0700, Dan Williams wrote: > Silently turn on DAX if HMAT says its ok? Yes, absolutely. I want my system to do the right thing by default, and if HMAT says bypassing the page cache is a clear advatange it should be the default. > I think we would instead > want a "-o autodax" for that case and then "-o dax" and "-o nodax" for > the force cases. Why? > I think it's easier to administer than the dax mount option. If > someone wants dax on only in a sub-tree they can set the flag on that > parent directory and have a policy in dax filesystems that children > inherit the dax policy from the parent. That seems a better > administrative model than trying to get it all right globally at mount > time. And why exactly? If DAX is faster for file a in directory X it will be just as fast for a file b in directory Y.