From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 53C8FC43334 for ; Mon, 13 Jun 2022 02:54:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238229AbiFMCyA (ORCPT ); Sun, 12 Jun 2022 22:54:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55744 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235700AbiFMCx6 (ORCPT ); Sun, 12 Jun 2022 22:53:58 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id A1B1C35872 for ; Sun, 12 Jun 2022 19:53:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1655088836; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=awNyHYB+B6d++/GUSUOZEZMC4V4Il/2xgLKKTfctnKo=; b=YXutdmp3VsWJmqQG7NIetHnTqzAXVxUtsCqEKlIsPTXg5D9waxHITTn5KiJGTY0FBL7fOO C13N8Ba7OT2090emTJSIgqIVGoZ1UpjuCsc5KrlObXOQMoqvOgZugOtzuQ0lgdZ1BmF9IN 4Xb9XkGNjMUoiKN7DQVY1DJoHmEFFKQ= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-31--GkFDRtPOaCAeJe8ZsfFcA-1; Sun, 12 Jun 2022 22:53:54 -0400 X-MC-Unique: -GkFDRtPOaCAeJe8ZsfFcA-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id D2EF482407B; Mon, 13 Jun 2022 02:53:53 +0000 (UTC) Received: from [10.22.16.100] (unknown [10.22.16.100]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3B5FC492C3B; Mon, 13 Jun 2022 02:53:53 +0000 (UTC) Message-ID: Date: Sun, 12 Jun 2022 22:53:53 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: [PATCH v11 3/8] cgroup/cpuset: Allow no-task partition to have empty cpuset.cpus.effective Content-Language: en-US To: Tejun Heo Cc: 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 , =?UTF-8?Q?Michal_Koutn=c3=bd?= References: <20220510153413.400020-1-longman@redhat.com> <20220510153413.400020-4-longman@redhat.com> From: Waiman Long In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.85 on 10.11.54.9 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/12/22 13:41, Tejun Heo wrote: > On Sun, Jun 12, 2022 at 07:40:25AM -1000, Tejun Heo wrote: >> Hello, >> >> Sorry about the long delay. >> >> On Tue, May 10, 2022 at 11:34:08AM -0400, Waiman Long wrote: >>> Once a partition with empty "cpuset.cpus.effective" is formed, no >>> new task can be moved into it until "cpuset.cpus.effective" becomes >>> non-empty. >> This is always true due to no-tasks-in-intermediate-cgroups requirement, >> right? > or rather, I should have asked, why does this need an explicit check? Without this patch, cpus.effective will never be empty. It just falls back to its parent if it becomes empty. Now with an empty cpus.effective, I am afraid that if a task is somehow moved to such a cpuset, something bad may happen. So I add this check as a safeguard. Cheers, Longman