From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([198.137.202.9]:48666 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751257AbdARGHm (ORCPT ); Wed, 18 Jan 2017 01:07:42 -0500 Date: Tue, 17 Jan 2017 22:07:40 -0800 From: willy@bombadil.infradead.org To: Dan Williams Cc: Ross Zwisler , lsf-pc@lists.linux-foundation.org, linux-fsdevel , "linux-nvdimm@lists.01.org" , linux-block@vger.kernel.org, Linux MM Subject: Re: [LSF/MM TOPIC] Future direction of DAX Message-ID: <20170118060740.GE18349@bombadil.infradead.org> References: <20170114002008.GA25379@linux.intel.com> <20170118052533.GA18349@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org On Tue, Jan 17, 2017 at 10:01:30PM -0800, Dan Williams wrote: > >> - Jan suggested [2] that we could use the radix tree as a cache to service DAX > >> faults without needing to call into the filesystem. Are there any issues > >> with this approach, and should we move forward with it as an optimization? > > > > Ahem. I believe I proposed this at last year's LSFMM. And I sent > > patches to start that work. And Dan blocked it. So I'm not terribly > > amused to see somebody else given credit for the idea. > > I "blocked" moving the phys to virt translation out of the driver > since that mapping lifetime is device specific. The problem is that DAX currently assumes that there *is* a block driver, and it might be a char device or no device at all (the two examples I gave earlier). > However, I think caching the file offset to physical sector/address > result is a great idea. OK, great. The lifetime problem I think you care about (hotplug) can be handled by removing all the cached entries for every file on every file on that block device ... I know there were prototype patches for that; did they ever get merged?