From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f72.google.com (mail-pg0-f72.google.com [74.125.83.72]) by kanga.kvack.org (Postfix) with ESMTP id 8E3316B0261 for ; Wed, 23 Nov 2016 03:37:24 -0500 (EST) Received: by mail-pg0-f72.google.com with SMTP id e9so14390616pgc.5 for ; Wed, 23 Nov 2016 00:37:24 -0800 (PST) Received: from mail-pf0-x242.google.com (mail-pf0-x242.google.com. [2607:f8b0:400e:c00::242]) by mx.google.com with ESMTPS id b34si4106173pli.224.2016.11.23.00.37.23 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 23 Nov 2016 00:37:23 -0800 (PST) Received: by mail-pf0-x242.google.com with SMTP id c4so395670pfb.3 for ; Wed, 23 Nov 2016 00:37:23 -0800 (PST) Subject: Re: [mm v2 0/3] Support memory cgroup hotplug References: <1479875814-11938-1-git-send-email-bsingharora@gmail.com> <20161123072543.GD2864@dhcp22.suse.cz> <342ebcca-b54c-4bc6-906b-653042caae06@gmail.com> <20161123080744.GG2864@dhcp22.suse.cz> From: Balbir Singh Message-ID: <61dc32fd-2802-6deb-24cf-fa11b5b31532@gmail.com> Date: Wed, 23 Nov 2016 19:37:16 +1100 MIME-Version: 1.0 In-Reply-To: <20161123080744.GG2864@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, Tejun Heo , Andrew Morton , Johannes Weiner , Vladimir Davydov On 23/11/16 19:07, Michal Hocko wrote: > On Wed 23-11-16 18:50:42, Balbir Singh wrote: >> >> >> On 23/11/16 18:25, Michal Hocko wrote: >>> On Wed 23-11-16 15:36:51, Balbir Singh wrote: >>>> In the absence of hotplug we use extra memory proportional to >>>> (possible_nodes - online_nodes) * number_of_cgroups. PPC64 has a patch >>>> to disable large consumption with large number of cgroups. This patch >>>> adds hotplug support to memory cgroups and reverts the commit that >>>> limited possible nodes to online nodes. >>> >>> Balbir, >>> I have asked this in the previous version but there still seems to be a >>> lack of information of _why_ do we want this, _how_ much do we save on >>> the memory overhead on most systems and _why_ the additional complexity >>> is really worth it. Please make sure to add all this in the cover >>> letter. >>> >> >> The data is in the patch referred to in patch 3. The order of waste was >> 200MB for 400 cgroup directories enough for us to restrict possible_map >> to online_map. These patches allow us to have a larger possible map and >> allow onlining nodes not in the online_map, which is currently a restriction >> on ppc64. > > How common is to have possible_map >> online_map? If this is ppc64 then > what is the downside of keeping the current restriction instead? > On my system CONFIG_NODE_SHIFT is 8, 256 nodes and possible_nodes are 2 The downside is the ability to hotplug and online an offline node. Please see http://www.spinics.net/lists/linux-mm/msg116724.html >> A typical system that I use has about 100-150 directories, depending on the >> number of users/docker instances/configuration/virtual machines. These numbers >> will only grow as we pack more of these instances on them. >> >> From a complexity view point, the patches are quite straight forward. > > Well, I would like to hear more about that. {get,put}_online_memory > at random places doesn't sound all that straightforward to me. > I thought those places were not random :) I tried to think them out as discussed with Vladimir. I don't claim the code is bug free, we can fix any bugs as we test this more. Balbir Singh. -- 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