Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758048AbaGWOmy (ORCPT ); Wed, 23 Jul 2014 10:42:54 -0400 Received: from zill.ext.symas.net ([69.43.206.106]:38788 "EHLO zill.ext.symas.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755904AbaGWOmv (ORCPT ); Wed, 23 Jul 2014 10:42:51 -0400 X-Greylist: delayed 1935 seconds by postgrey-1.27 at vger.kernel.org; Wed, 23 Jul 2014 10:42:51 EDT Message-ID: <53CFC258.6050803@symas.com> Date: Wed, 23 Jul 2014 07:10:32 -0700 From: Howard Chu User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:29.0) Gecko/20100101 Firefox/29.0 SeaMonkey/2.26a1 MIME-Version: 1.0 To: Matthew Wilcox , Linux Kernel Mailing List Subject: Re: [PATCH v8 00/22] Support ext4 on NV-DIMMs References: <00ad731b459e32ce965af8530bcd611a141e41b6.1406058387.git.matthew.r.wilcox@intel.com> <20140723121025.GE10317@node.dhcp.inet.fi> <20140723135514.GB6754@linux.intel.com> In-Reply-To: <20140723135514.GB6754@linux.intel.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Matthew Wilcox wrote: > One of the primary uses for NV-DIMMs is to expose them as a block device > and use a filesystem to store files on the NV-DIMM. While that works, > it currently wastes memory and CPU time buffering the files in the page > cache. We have support in ext2 for bypassing the page cache, but it > has some races which are unfixable in the current design. This series > of patches rewrite the underlying support, and add support for direct > access to ext4. This is an awful lot of work to go thru just to get a glorified ext4 RAMdisk. RAMdisks are one of the worst possible uses for RAM, requiring users to explicitly copy files to them before getting any benefit. Using RAM for a page cache instead brings benefits to all file accesses without requiring any user intervention. If the NVDIMM range was reserved for exclusive use of the page cache, then you would have an avenue to get persistence/safety for every filesystem mounted on a machine, not just a special case ext4. -- -- Howard Chu CTO, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/project/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/