Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751661AbdGZRUO (ORCPT ); Wed, 26 Jul 2017 13:20:14 -0400 Received: from bombadil.infradead.org ([65.50.211.133]:60869 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751202AbdGZRUL (ORCPT ); Wed, 26 Jul 2017 13:20:11 -0400 Date: Wed, 26 Jul 2017 10:20:11 -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: <20170726172011.GA30142@infradead.org> References: <1500552639-18523-1-git-send-email-sunqiuyang@huawei.com> <20170726072634.GA4684@infradead.org> <20170726170147.GA31930@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: 813 Lines: 17 On Wed, Jul 26, 2017 at 10:11:08AM -0700, Dan Williams wrote: > Until HMAT came along we had no data in the kernel how to pick a sane > default, but we could now very easily make a "if pmem performance < > dram, disable dax by default" policy in the kernel. I'd rather do it the other way around - if HMAT is present and pmem performance >= dram use dax. Else require the explicit -o dax for now to enable it. If an explicit -o nodax is specified disable DAX even if HMAT says it is faster. > The question for this patch is do we want to add yet another > filesystem that adds "-o dax" or require use of per-inode flags to > enable dax. Please stick to the mount option. After spending a lot of time with DAX and various memory techologies I'm pretty confident that the inode flag is the wrong thing to do.