From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755515Ab3LRRvv (ORCPT ); Wed, 18 Dec 2013 12:51:51 -0500 Received: from mail-oa0-f51.google.com ([209.85.219.51]:46401 "EHLO mail-oa0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755433Ab3LRRvs (ORCPT ); Wed, 18 Dec 2013 12:51:48 -0500 Message-ID: <52B1E0A2.2030202@landley.net> Date: Wed, 18 Dec 2013 11:51:30 -0600 From: Rob Landley User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Dave Young , akpm@linux-foundation.org, gregkh@linuxfoundation.org, grant.likely@secretlab.ca, sebastian.capella@linaro.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] use initmpfs even if there's root= cmdline References: <20131212092542.GA14218@dhcp-16-126.nay.redhat.com> <20131213023814.GA5519@dhcp-16-126.nay.redhat.com> In-Reply-To: <20131213023814.GA5519@dhcp-16-126.nay.redhat.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 On 12/12/13 20:38, Dave Young wrote: > On 12/12/13 at 05:25pm, Dave Young wrote: >> >> Current code use ramfs instead of tmpfs for stub when root= defined. >> >> But for real use case with initramfs, usually there's like cmdline like >> root=UUID=$UUID the root dev is the real device. For that case we have >> no way to use initmpfs, thus this patch removes the limitation so tmpfs >> can benefit more people. The reason I did that was if you specify a root= then you don't want to _stay_ on rootfs. You specify root= so either the kernel does switch_root for you, or so rootfs does a swich_root at the end. The point of initmpfs is that when rootfs _is_ the "real" root device, it can benefit from being tmpfs. When you're just goign to switch to a different root device, tmpfs doesn't make much difference. > Discussed with Vivek Goyal about the kdump use case, I missed one thing that > tmpfs has default size limit though we can tune it. > > So I will think more about it, will address this later, please ignore this > patch. I have a vague todo item of feeding rootflags= through to initmpfs, but that's really intended to specify flags for root=. There isn't really an existing command line option to specify initramfs flags because ramfs doesn't care. It was one of those "only parse rootflags= for initmpfs when there's no root=" vs "create a new rdrootflags= ala rdinit= even though that's a subtly wrong name these days..." and it went on the todo list because neither approach was obviously superior. Happy to take suggestions and whip up a patch if this is inconveniencing somebody. :) > Thanks > Dave Rob