From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f179.google.com (mail-pd0-f179.google.com [209.85.192.179]) by kanga.kvack.org (Postfix) with ESMTP id 46FAC900021 for ; Mon, 27 Oct 2014 14:48:15 -0400 (EDT) Received: by mail-pd0-f179.google.com with SMTP id g10so6196251pdj.10 for ; Mon, 27 Oct 2014 11:48:14 -0700 (PDT) Received: from mga14.intel.com (mga14.intel.com. [192.55.52.115]) by mx.google.com with ESMTP id qp3si11128153pac.147.2014.10.27.11.48.13 for ; Mon, 27 Oct 2014 11:48:14 -0700 (PDT) Date: Mon, 27 Oct 2014 14:48:09 -0400 From: Matthew Wilcox Subject: Re: Progress on system crash traces with LTTng using DAX and pmem Message-ID: <20141027184809.GW11522@wil.cx> References: <1254279794.1957.1414240389301.JavaMail.zimbra@efficios.com> <465653369.1985.1414241485934.JavaMail.zimbra@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <465653369.1985.1414241485934.JavaMail.zimbra@efficios.com> Sender: owner-linux-mm@kvack.org List-ID: To: Mathieu Desnoyers Cc: Matthew Wilcox , Ross Zwisler , lttng-dev , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Sat, Oct 25, 2014 at 12:51:25PM +0000, Mathieu Desnoyers wrote: > A quick follow up on my progress on using DAX and pmem with > LTTng. I've been able to successfully gather a user-space > trace into buffers mmap'd into an ext4 filesystem within > a pmem block device mounted with -o dax to bypass the page > cache. After a soft reboot, I'm able to mount the partition > again, and gather the very last data collected in the buffers > by the applications. I created a "lttng-crash" program that > extracts data from those buffers and converts the content > into a readable Common Trace Format trace. So I guess > you have a use-case for your patchsets on commodity hardware > right there. :) Sweet! > I've been asked by my customers if DAX would work well with > mtd-ram, which they are using. To you foresee any roadblock > with this approach ? Looks like we'd need to add support to mtd-blkdevs.c for DAX. I assume they're already using one of the block-based ways to expose MTD to filesystems, rather than jffs2/logfs/ubifs? I'm thinking we might want to add a flag somewhere in the block_dev / bdi that indicates whether DAX is supported. Currently we rely on whether ->direct_access is present in the block_device_operations to indicate that, so we'd have to have two block_dev_operations in mtd-blkdevs, depending on whether direct access is supported by the underlying MTD device. Not a show-stopper. > Please keep me in CC on your next patch versions. I'm willing > to spend some more time reviewing them if needed. By the way, > do you guys have a target time-frame/kernel version you aim > at for getting this work upstream ? We're trying to get it upstream ASAP. We've been working on it publically since December last year, and it's getting frustrating that it's not upstream already. I sent a v12 a few minutes before you sent this message ... I thought git would add you to the cc's since your Reviewed-by is on some of the patches. -- 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