From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932813AbaCQLni (ORCPT ); Mon, 17 Mar 2014 07:43:38 -0400 Received: from mta-out.inet.fi ([195.156.147.13]:40567 "EHLO jenni2.inet.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932672AbaCQLnh (ORCPT ); Mon, 17 Mar 2014 07:43:37 -0400 Date: Mon, 17 Mar 2014 13:43:21 +0200 From: "Kirill A. Shutemov" To: Matthew Wilcox Cc: Toshi Kani , kirill.shutemov@linux.intel.com, david@fromorbit.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH] Support map_pages() for DAX Message-ID: <20140317114321.GA30191@node.dhcp.inet.fi> References: <1394838199-29102-1-git-send-email-toshi.kani@hp.com> <20140314233233.GA8310@node.dhcp.inet.fi> <20140316024613.GF6091@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140316024613.GF6091@linux.intel.com> User-Agent: Mutt/1.5.22.1-rc1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Mar 15, 2014 at 10:46:13PM -0400, Matthew Wilcox wrote: > On Sat, Mar 15, 2014 at 01:32:33AM +0200, Kirill A. Shutemov wrote: > > Side note: I'm sceptical about whole idea to use i_mmap_mutux to protect > > against truncate. It will not scale good enough comparing lock_page() > > with its granularity. > > I'm actually working on this now. The basic idea is to put an entry in > the radix tree for each page. For zero pages, that's a pagecache page. > For pages that map to the media, it's an exceptional entry. Radix tree > exceptional entries take two bits, leaving us with 30 or 62 bits depending > on sizeof(void *). We can then take two more bits for Dirty and Lock, > leaving 28 or 60 bits that we can use to cache the PFN on the page, > meaning that we won't have to call the filesystem's get_block as often. Sound reasonable to me. Implementation of ->map_pages should be trivial with this. Few questions: - why would you need Dirty for DAX? - are you sure that 28 bits is enough for PFN everywhere? ARM with LPAE can have up to 40 physical address lines. Is there any 32-bit machine with more address lines? -- Kirill A. Shutemov