From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f179.google.com (mail-wi0-f179.google.com [209.85.212.179]) by kanga.kvack.org (Postfix) with ESMTP id 968BE82F65 for ; Wed, 21 Oct 2015 05:00:28 -0400 (EDT) Received: by wicll6 with SMTP id ll6so64074338wic.1 for ; Wed, 21 Oct 2015 02:00:28 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id bc8si10164533wjc.13.2015.10.21.02.00.27 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 21 Oct 2015 02:00:27 -0700 (PDT) Subject: Re: [PATCH V7] mm: memory hot-add: memory can not be added to movable zone defaultly References: <1444633113-27607-1-git-send-email-liuchangsheng@inspur.com> <561E8056.7050609@suse.cz> <5626F667.9000003@inspur.com> From: Vlastimil Babka Message-ID: <56275423.6050506@suse.cz> Date: Wed, 21 Oct 2015 11:00:19 +0200 MIME-Version: 1.0 In-Reply-To: <5626F667.9000003@inspur.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Changsheng Liu , akpm@linux-foundation.org, isimatu.yasuaki@jp.fujitsu.com, yasu.isimatu@gmail.com, tangchen@cn.fujitsu.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, wangnan0@huawei.com, dave.hansen@intel.com, yinghai@kernel.org, toshi.kani@hp.com, qiuxishi@huawei.com, wunan@inspur.com, yanxiaofeng@inspur.com, fandd@inspur.com, Changsheng Liu On 10/21/2015 04:20 AM, Changsheng Liu wrote: > > > a?? 2015/10/15 0:18, Vlastimil Babka a??e??: >> On 10/12/2015 08:58 AM, Changsheng Liu wrote: >>> From: Changsheng Liu >>> >>> After the user config CONFIG_MOVABLE_NODE, >>> When the memory is hot added, should_add_memory_movable() return 0 >>> because all zones including ZONE_MOVABLE are empty, >>> so the memory that was hot added will be assigned to ZONE_NORMAL >>> and ZONE_NORMAL will be created firstly. >>> But we want the whole node to be added to ZONE_MOVABLE by default. >>> >>> So we change should_add_memory_movable(): if the user config >>> CONFIG_MOVABLE_NODE and sysctl parameter hotadd_memory_as_movable is 1 >>> and the ZONE_NORMAL is empty or the pfn of the hot-added memory >>> is after the end of the ZONE_NORMAL it will always return 1 >>> and then the whole node will be added to ZONE_MOVABLE by default. >>> If we want the node to be assigned to ZONE_NORMAL, >>> we can do it as follows: >>> "echo online_kernel > /sys/devices/system/memory/memoryXXX/state" >>> >>> By the patch, the behavious of kernel is changed by sysctl, >>> user can automatically create movable memory >>> by only the following udev rule: >>> SUBSYSTEM=="memory", ACTION=="add", >>> ATTR{state}=="offline", ATTR{state}="online" > I'm sorry for replying you so late due to the busy business trip. >> So just to be clear, we are adding a new sysctl, because the existing >> movable_node kernel option, which is checked by movable_node_is_enabled(), and >> does the same thing for non-hot-added-memory (?) cannot be reused for hot-added >> memory, as that would be a potentially surprising behavior change? Correct? Then >> this should be mentioned in the changelog too, and wherever "movable_node" is >> documented should also mention the new sysctl. Personally, I would expect >> movable_node to affect hot-added memory as well, and would be surprised that it >> doesn't... > I think it can let the user decides when to use this feature. > The user can enable the feature when making the hot_added memory > of a node movable and > make the feature disable to assign the hot_added memory of the next > node to ZONE_NORMAL . So you mean sysctl is more flexible than boot option. OK, but wasn't such flexibility already provided by "echo online_kernel" vs "echo online_movable"? It doesn't sound like a strong reason for a new sysctl? Not doing surprising behavior change maybe does... -- 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