From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx153.postini.com [74.125.245.153]) by kanga.kvack.org (Postfix) with SMTP id C809B6B0031 for ; Sat, 27 Jul 2013 13:45:06 -0400 (EDT) Received: by mail-ee0-f46.google.com with SMTP id d41so2086978eek.19 for ; Sat, 27 Jul 2013 10:45:05 -0700 (PDT) Message-ID: <51F40570.9050209@gmail.com> Date: Sat, 27 Jul 2013 19:37:52 +0200 From: Marco Stornelli MIME-Version: 1.0 Subject: Re: [PATCH RFC] pram: persistent over-kexec memory file system References: <1374841763-11958-1-git-send-email-vdavydov@parallels.com> <51F3EA2A.3090905@gmail.com> <51F404D0.6070004@parallels.com> In-Reply-To: <51F404D0.6070004@parallels.com> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Vladimir Davydov Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, criu@openvz.org, devel@openvz.org, xemul@parallels.com Il 27/07/2013 19:35, Vladimir Davydov ha scritto: > On 07/27/2013 07:41 PM, Marco Stornelli wrote: >> Il 26/07/2013 14:29, Vladimir Davydov ha scritto: >>> Hi, >>> >>> We want to propose a way to upgrade a kernel on a machine without >>> restarting all the user-space services. This is to be done with CRIU >>> project, but we need help from the kernel to preserve some data in >>> memory while doing kexec. >>> >>> The key point of our implementation is leaving process memory in-place >>> during reboot. This should eliminate most io operations the services >>> would produce during initialization. To achieve this, we have >>> implemented a pseudo file system that preserves its content during >>> kexec. We propose saving CRIU dump files to this file system, kexec'ing >>> and then restoring the processes in the newly booted kernel. >>> >> >> http://pramfs.sourceforge.net/ > > AFAIU it's a bit different thing: PRAMFS as well as pstore, which has > already been merged, requires hardware support for over-reboot > persistency, so called non-volatile RAM, i.e. RAM which is not directly > accessible and so is not used by the kernel. On the contrary, what we'd > like to have is preserving usual RAM on kexec. It is possible, because > RAM is not reset during kexec. This would allow leaving applications > working set as well as filesystem caches in place, speeding the reboot > process as a whole and reducing the downtime significantly. > > Thanks. Actually not. You can use normal system RAM reserved at boot with mem parameter without any kernel change. Until an hard reset happens, that area will be "persistent". Regards, Marco -- 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