From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal =?iso-8859-1?Q?Koutn=FD?= Subject: Re: [PATCH v7 5/6] cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst Date: Mon, 30 Aug 2021 19:59:43 +0200 Message-ID: References: <20210825213750.6933-1-longman@redhat.com> <20210825213750.6933-6-longman@redhat.com> <32e27fcc-32f1-b26c-ae91-9e03f7e433af@redhat.com> <392c3724-f583-c7fc-cfa1-a3f1665114c9@redhat.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1630346385; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Fjtm8tVefXUCT0rdTzMn/o5zpc91NrF6pXy1z50nDUM=; b=TyI+3u+QEneileBnDmwJhe/7GU/cZ4f+Sj8PsvZ9ugakdDVaT8ur0+WioUJKotS8fyURo0 Mm12eWM1b0hCFWGb0F0M+ECUj56MCl6ARx+3TzD2Y8ZHaqgpxOq8DgRVIyvlvXxef349Py dUMXeDS74InyxljMGcbhds/MtAMoLJk= Content-Disposition: inline In-Reply-To: <392c3724-f583-c7fc-cfa1-a3f1665114c9@redhat.com> List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Waiman Long Cc: Tejun Heo , Zefan Li , Johannes Weiner , Jonathan Corbet , Shuah Khan , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, Andrew Morton , Roman Gushchin , Phil Auld , Peter Zijlstra , Juri Lelli , Frederic Weisbecker , Marcelo Tosatti Hello. On Fri, Aug 27, 2021 at 06:50:10PM -0400, Waiman Long wrote: > So the new rules will be: When I followed the thread, it seemed to me you're talking past each other a bit. I'd suggest the following terminology: - config space: what's written by the user and saved, - reality space: what's currently available (primarily subject to on-/offlinng but I think it'd be helpful to consider here also what's given by the parent), - effect space: what's actually possible and happening. Not all elements of config_space x reality_space (Cartesian product) can be represented in the effect_space (e.g. root partition with no (effective) cpus). IIUC, Waiman's "high bar" is supposed to be defined over transitions in the config_space. However, there can be independent changes in the reality_space so the rules should be actually formulated in the effect_space: The conditions for being a valid partition root rewritten into the effect space: > 1) The "cpuset.cpus" is not empty and the list of CPUs are exclusive. - effective CPUs are non-empty and exclusive wrt siblings - (E.g. setting empty cpuset.cpus might be possible but it invalidates the partition root, same as offlining or removal by an ancestor.) > 2) The parent cgroup is a partition root (can be an invalid one). - parent cgroup is a (valid) partition - (Being valid partition means owning "stolen" cpus from the parent, if the parent is not valid partition itself, you can't steal what is not owned.) - (And I think it's OK that: "the child partitions will stay invalid forever unless the parent become a valid partition again" [1].) > 3) The "cpuset.cpus" is a subset of the parent's cpuset.cpus.allowed. - I'm not sure what is the use of this condition (together with the rewrite of the 1st condition which covers effective cpus). I think it would make sense if being a valid parition root guaranteed that all configured cpuset.cpus will be available, however, that's not the case IIUC (e.g. due to offlining). > 4) No child cgroup with cpuset enabled. - A child cgroup with cpuset enabled is OK in the effect space (achievable by switching first and creating children later). - For technical reasons this may be a condition on the transitions in the config_space. Generally, most config changes should succeed and user should check (or watch) how they landed in combination with the reality_space. Regards, Michal [1] This follows the general model where ancestors can "preempt" resources from their subtree.