From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f69.google.com (mail-pg0-f69.google.com [74.125.83.69]) by kanga.kvack.org (Postfix) with ESMTP id E8A5D6B0266 for ; Wed, 18 Jan 2017 01:07:42 -0500 (EST) Received: by mail-pg0-f69.google.com with SMTP id 204so5423841pge.5 for ; Tue, 17 Jan 2017 22:07:42 -0800 (PST) Received: from bombadil.infradead.org (bombadil.infradead.org. [2001:1868:205::9]) by mx.google.com with ESMTPS id d65si27362990pfl.73.2017.01.17.22.07.42 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 17 Jan 2017 22:07:42 -0800 (PST) Date: Tue, 17 Jan 2017 22:07:40 -0800 From: willy@bombadil.infradead.org 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 Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: 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 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? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org