From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f182.google.com (mail-pf0-f182.google.com [209.85.192.182]) by kanga.kvack.org (Postfix) with ESMTP id 341A76B0259 for ; Wed, 16 Dec 2015 05:42:07 -0500 (EST) Received: by mail-pf0-f182.google.com with SMTP id e66so10701436pfe.0 for ; Wed, 16 Dec 2015 02:42:07 -0800 (PST) Received: from szxga02-in.huawei.com ([119.145.14.65]) by mx.google.com with ESMTPS id jh7si8632934pac.115.2015.12.16.02.42.01 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 16 Dec 2015 02:42:06 -0800 (PST) Message-ID: <56713D17.1080002@huawei.com> Date: Wed, 16 Dec 2015 18:29:43 +0800 From: Xishi Qiu MIME-Version: 1.0 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 Sender: owner-linux-mm@kvack.org List-ID: To: Vitaly Kuznetsov Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, 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 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 -- 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