From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752263AbbLPKmL (ORCPT ); Wed, 16 Dec 2015 05:42:11 -0500 Received: from szxga02-in.huawei.com ([119.145.14.65]:9708 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750868AbbLPKmJ (ORCPT ); Wed, 16 Dec 2015 05:42:09 -0500 Message-ID: <56713D17.1080002@huawei.com> Date: Wed, 16 Dec 2015 18:29:43 +0800 From: Xishi Qiu User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:12.0) Gecko/20120428 Thunderbird/12.0.1 MIME-Version: 1.0 To: Vitaly Kuznetsov 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> In-Reply-To: <87k2oevjkn.fsf@vitty.brq.redhat.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.177.25.179] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A020201.56713D26.010D,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2013-06-18 04:22:30, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: 90dddc4c0bccef5934d2d54a30e1dd94 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > > 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. Thanks, Xishi Qiu