From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5C2483B6350 for ; Fri, 29 May 2026 21:28:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780090145; cv=none; b=nRF1lz8XVFtjMDKzHyRpq8vH2lkIZa/6DBeAJ4D71Qxw5Z4819G6pd0HJCkajStt66uhc3NhsFpmPeR8Np9UWseLvX/NQFl0fw3IsWr0idxfjBnVV/Hq9CIqc+HJx+C9vrZ5nD7n1T76X486IM9nXqp/+XpMtn7N85R6LkOCkNA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780090145; c=relaxed/simple; bh=LLl8YSsAIOLYo3nmxGvTC6JxMFgJ1qBEOowVfPSxbTU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=UOT/JIzGoa1NpHIYoFmvunzLC9VJf0505Tixqa+WMXBm2L9DzaY3Tp+GYPWK11zQux8g0lnkqU5ZueEVCc2wvNcvqXDZK9kzihWt/MdC9C1uCIhPPJi0F79zM5CvTXEn6P/LQd1adHHTvlAldzAojO00IJii0ACkWwK/eLL0W/o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=fAdCyinI; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="fAdCyinI" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1780090138; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=no9433L2vTEzwg3X66k17tcFeYU0ZZ98IuFscRMp3x4=; b=fAdCyinIiFXvngjfS68phNx+8v6VWntymKJ7/jke/90cUJHfNEj9a+7XENDbM5zFgeXvUi eQQTebtOm1yTNzO+f6NOa1bqQmU8voQdULtJ2S9TzJV7nU/uZ/VgrormA4SH/WWaASzoYc +vhEHUpHjQUk0kbjL/ckFIDIx+jn3vg= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-54-3wmb1PK7MiGmJyc436yqig-1; Fri, 29 May 2026 17:28:55 -0400 X-MC-Unique: 3wmb1PK7MiGmJyc436yqig-1 X-Mimecast-MFC-AGG-ID: 3wmb1PK7MiGmJyc436yqig_1780090133 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 49F0F18005B9; Fri, 29 May 2026 21:28:53 +0000 (UTC) Received: from llong-thinkpadp16vgen1.westford.csb (unknown [10.22.64.54]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 355B419560A3; Fri, 29 May 2026 21:28:51 +0000 (UTC) From: Waiman Long To: Chen Ridong , Tejun Heo , Johannes Weiner , =?UTF-8?q?Michal=20Koutn=C3=BD?= , Peter Zijlstra Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Aaron Tomlin , Guopeng Zhang , Waiman Long , Ridong Chen Subject: [PATCH-next v4 4/6] cgroup/cpuset: Made cpuset_attach_old_cs track task group leaders Date: Fri, 29 May 2026 17:21:06 -0400 Message-ID: <20260529212108.120506-5-longman@redhat.com> In-Reply-To: <20260529212108.120506-1-longman@redhat.com> References: <20260529212108.120506-1-longman@redhat.com> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 There are two possible ways that migration of tasks from multiple source cpusets to a target cpuset can happen. Either a multithread application with threads in different cpusets is wholely moved to a new cpuset or disabling of v2 cpuset controller will move all the tasks in child cpusets to the parent cpuset. In the former case, it is the mm setting of the group leader that really matters. So cpuset_attach_old_cs should track the oldcs of the thread leader. In the latter case, effective_mems of child cpusets must always be a subset of the parent. So no real page migration will be necessary no matter which child cpuset is selected as cpuset_attach_old_cs. IOW, cpuset_attach_old_cs should be updated to match the latest task group leader in cpuset_can_attach(). Suggested-by: Ridong Chen Signed-off-by: Waiman Long --- kernel/cgroup/cpuset.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 0f93f3d84494..0bb63a9cda0b 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -1111,6 +1111,20 @@ static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs, /* * cpuset_can_attach() and cpuset_attach() specific internal data * Protected by cpuset_mutex + * + * The cpuset_attach_old_cs is used mainly by cpuset_migrate_mm() to get the + * old_mems_allowed value. There are two ways that many-to-one cpuset migration + * can happen: + * 1) A multithread application with threads in different cpusets is wholely + * moved to a new cpuset. + * 2) Disabling v2 cpuset controller will move all the tasks in child cpusets + * to the parent cpuset. + * + * In the former case, it is the mm setting of the group leader that really + * matters. So cpuset_attach_old_cs should track the oldcs of the thread + * leader. In the latter case, effective_mems of child cpusets must always + * be a subset of the parent. So no real page migration will be necessary no + * matter which child cpuset is selected as cpuset_attach_old_cs. */ static struct cpuset *cpuset_attach_old_cs; static bool attach_cpus_updated; @@ -3091,6 +3105,10 @@ static int cpuset_can_attach(struct cgroup_taskset *tset) if (ret) goto out_unlock; + /* Update cpuset_attach_old_cs to the latest group leader */ + if (task == task->group_leader) + cpuset_attach_old_cs = task_cs(task); + if (setsched_check) { ret = security_task_setscheduler(task); if (ret) -- 2.54.0