From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-x243.google.com (mail-pg0-x243.google.com [IPv6:2607:f8b0:400e:c05::243]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3tNvf51tNpzDw2G for ; Wed, 23 Nov 2016 18:50:53 +1100 (AEDT) Received: by mail-pg0-x243.google.com with SMTP id p66so516493pga.2 for ; Tue, 22 Nov 2016 23:50:53 -0800 (PST) Subject: Re: [mm v2 0/3] Support memory cgroup hotplug To: Michal Hocko References: <1479875814-11938-1-git-send-email-bsingharora@gmail.com> <20161123072543.GD2864@dhcp22.suse.cz> Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, Tejun Heo , Andrew Morton , Johannes Weiner , Vladimir Davydov From: Balbir Singh Message-ID: <342ebcca-b54c-4bc6-906b-653042caae06@gmail.com> Date: Wed, 23 Nov 2016 18:50:42 +1100 MIME-Version: 1.0 In-Reply-To: <20161123072543.GD2864@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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. 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. > I still didn't get to look into those patches because I am swamped with > other things but to be honest I do not really see a strong justification > to make it high priority for me. > I am OK if you need more time to review them, but I've been pushing them to fix the cases I've mentioned above. Balbir Singh.