Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751876AbbGEN3l (ORCPT ); Sun, 5 Jul 2015 09:29:41 -0400 Received: from mail-wi0-f175.google.com ([209.85.212.175]:33531 "EHLO mail-wi0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751290AbbGEN3b (ORCPT ); Sun, 5 Jul 2015 09:29:31 -0400 Message-ID: <55993138.3040307@plexistor.com> Date: Sun, 05 Jul 2015 16:29:28 +0300 From: Boaz Harrosh User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: "Theodore Ts'o" , Matthew Wilcox , Matthew Wilcox , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Alexander Viro , Andreas Dilger , linux-ext4@vger.kernel.org Subject: Re: [PATCH v2 3/6] ext4: Use ext4_get_block_write() for DAX References: <1435934443-17090-1-git-send-email-matthew.r.wilcox@intel.com> <1435934443-17090-4-git-send-email-matthew.r.wilcox@intel.com> <20150703183027.GH9456@thunk.org> <20150703184824.GA13681@linux.intel.com> <20150703190703.GK9456@thunk.org> In-Reply-To: <20150703190703.GK9456@thunk.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1847 Lines: 50 On 07/03/2015 10:07 PM, Theodore Ts'o wrote: > On Fri, Jul 03, 2015 at 02:48:24PM -0400, Matthew Wilcox wrote: >> >> At boot, I "modprobe pmem". > > Is there a reason why it's important to build and load pmem as a > module? If I use CONFIG_BLK_DEV_PMEM=y (which is more convenient > given how I launch my KVM test appliance), should I expect any > problems? > This (=y) should work fine. We use it a lot. (with KVM even boot an image with -dax, with a trick) Note that DAX need not be tested with pmem only, you can always use brd at any given point without any reboot. One more trick for xfstest I use: memmap=2G!4G,2G!6G And have two pmem0/1 and don't need to bother with any fdisk. Do need to mkfs every boot though. BTW: with kvm a reboot with above memmap will give you back the exact same memory. halt and "virsh start" is a different story. > I assume that this won't detect any bugs caused by missing CLFLUSH > instructions, but I assume that when using NVM as a block device, this > isn't much of an issue, as long as we don't care about torn writes? > (How using NVM with metdata checksums, or any checksums for that > matter, seems to be an interesting question --- how do we recover from > a checksum failure after a power failure?) > Currently pmem maps a very-(very) slow ioremap_nocache. So any Kernel memory access should be pmem persistent. For a real world faster ioremap, there are few major pieces still missing in the stack to make it persistent. Note the even today with ioremap_nocache, any application mmap (like git) is not persistent. > - Ted Cheers Boaz -- 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/