From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754639AbbLPKxp (ORCPT ); Wed, 16 Dec 2015 05:53:45 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52910 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754573AbbLPKxm (ORCPT ); Wed, 16 Dec 2015 05:53:42 -0500 From: Vitaly Kuznetsov To: Xishi Qiu Cc: , , , Jonathan Corbet , "Greg Kroah-Hartman" , Daniel Kiper , Dan Williams , Tang Chen , David Vrabel , "David Rientjes" , Andrew Morton , Naoya Horiguchi , Gu Zheng , Mel Gorman , "K. Y. Srinivasan" , yanxiaofeng , Changsheng Liu , Kay Sievers Subject: Re: [PATCH RFC] memory-hotplug: add automatic onlining policy for the newly added memory References: <1450202753-5556-1-git-send-email-vkuznets@redhat.com> <5670D83E.9040407@huawei.com> <87k2oevjkn.fsf@vitty.brq.redhat.com> <56713D17.1080002@huawei.com> Date: Wed, 16 Dec 2015 11:53:35 +0100 In-Reply-To: <56713D17.1080002@huawei.com> (Xishi Qiu's message of "Wed, 16 Dec 2015 18:29:43 +0800") Message-ID: <8737v2vf4g.fsf@vitty.brq.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Xishi Qiu writes: > On 2015/12/16 17:17, Vitaly Kuznetsov wrote: > >> Xishi Qiu writes: >> >>> On 2015/12/16 2:05, Vitaly Kuznetsov wrote: >>> >>>> Currently, all newly added memory blocks remain in 'offline' state unless >>>> someone onlines them, some linux distributions carry special udev rules >>>> like: >>>> >>>> SUBSYSTEM=="memory", ACTION=="add", ATTR{state}=="offline", ATTR{state}="online" >>>> >>>> to make this happen automatically. This is not a great solution for virtual >>>> machines where memory hotplug is being used to address high memory pressure >>>> situations as such onlining is slow and a userspace process doing this >>>> (udev) has a chance of being killed by the OOM killer as it will probably >>>> require to allocate some memory. >>>> >>>> Introduce default policy for the newly added memory blocks in >>>> /sys/devices/system/memory/hotplug_autoonline file with two possible >>>> values: "offline" (the default) which preserves the current behavior and >>>> "online" which causes all newly added memory blocks to go online as >>>> soon as they're added. >>>> >>>> Cc: Jonathan Corbet >>>> Cc: Greg Kroah-Hartman >>>> Cc: Daniel Kiper >>>> Cc: Dan Williams >>>> Cc: Tang Chen >>>> Cc: David Vrabel >>>> Cc: David Rientjes >>>> Cc: Andrew Morton >>>> Cc: Naoya Horiguchi >>>> Cc: Gu Zheng >>>> Cc: Xishi Qiu >>>> Cc: Mel Gorman >>>> Cc: "K. Y. Srinivasan" >>>> Signed-off-by: Vitaly Kuznetsov >>>> --- >>>> - I was able to find previous attempts to fix the issue, e.g.: >>>> http://marc.info/?l=linux-kernel&m=137425951924598&w=2 >>>> http://marc.info/?l=linux-acpi&m=127186488905382 >>>> but I'm not completely sure why it didn't work out and the solution >>>> I suggest is not 'smart enough', thus 'RFC'. >>> >>> + CC: >>> yanxiaofeng@inspur.com >>> liuchangsheng@inspur.com >>> >>> Hi Vitaly, >>> >>> Why not use udev rule? I think it can online pages automatically. >>> >> >> Two main reasons: >> 1) I remember someone saying "You never need a mouse in order to add >> another mouse to the kernel" -- but we we need memory to add more >> memory. Udev has a chance of being killed by the OOM killer as >> performing an action will probably require to allocate some >> memory. Other than that udev actions are generally slow compared to what >> we can do in kernel. > > Hi Vitaly, > > So why we add memory when there is almost no free memory left? > I think the administrator should add memory when the free memory is low > or he should do something to stop free memory become worse. I have virtual machines use-case in my mind where hypervisor adds new memory on high memory pressure reports from the guest (e.g. Hyper-V behaves like that). This is an automatic action. > >> >> 2) I agree with Kay that '... unconditional hotplug loop through >> userspace is absolutely pointless' (https://lkml.org/lkml/2013/7/25/354). >> (... and I should had add him to CC, adding now). Udev maintainers >> refused to add a rule for unconditional memory onlining to udev and now >> linux distros have to carry such custom rules. >> > > If the administrator don't know how to config the udev, he could use sysfs > (echo 1 > /sys/devices/system/node/nodeXX/memoryXX/online) to online it, > or write a script to do this. Oh, no, I'm not taking about manual actions here. My suggestion doesn't eliminate this possibility and it doesn't even change the default -- memory blocks stay in 'offline' state unless someone requests the auto-online policy. -- Vitaly