From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751643AbdB0PtX (ORCPT ); Mon, 27 Feb 2017 10:49:23 -0500 Received: from mx2.suse.de ([195.135.220.15]:48530 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751251AbdB0PtV (ORCPT ); Mon, 27 Feb 2017 10:49:21 -0500 Date: Mon, 27 Feb 2017 16:43:04 +0100 From: Michal Hocko To: Heiko Carstens Cc: Vitaly Kuznetsov , linux-mm@kvack.org, Andrew Morton , Greg KH , "K. Y. Srinivasan" , David Rientjes , Daniel Kiper , linux-api@vger.kernel.org, LKML , linux-s390@vger.kernel.org, xen-devel@lists.xenproject.org, linux-acpi@vger.kernel.org Subject: Re: [RFC PATCH] mm, hotplug: get rid of auto_online_blocks Message-ID: <20170227154304.GK26504@dhcp22.suse.cz> References: <20170227092817.23571-1-mhocko@kernel.org> <87lgssvtni.fsf@vitty.brq.redhat.com> <20170227112510.GA4129@osiris> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170227112510.GA4129@osiris> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 27-02-17 12:25:10, Heiko Carstens wrote: > On Mon, Feb 27, 2017 at 11:02:09AM +0100, Vitaly Kuznetsov wrote: > > A couple of other thoughts: > > 1) Having all newly added memory online ASAP is probably what people > > want for all virtual machines. > > This is not true for s390. On s390 we have "standby" memory that a guest > sees and potentially may use if it sets it online. Every guest that sets > memory offline contributes to the hypervisor's standby memory pool, while > onlining standby memory takes memory away from the standby pool. > > The use-case is that a system administrator in advance knows the maximum > size a guest will ever have and also defines how much memory should be used > at boot time. The difference is standby memory. > > Auto-onlining of standby memory is the last thing we want. > > > Unfortunately, we have additional complexity with memory zones > > (ZONE_NORMAL, ZONE_MOVABLE) and in some cases manual intervention is > > required. Especially, when further unplug is expected. > > This also is a reason why auto-onlining doesn't seem be the best way. Can you imagine any situation when somebody actually might want to have this knob enabled? From what I understand it doesn't seem to be the case. -- Michal Hocko SUSE Labs