From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 9E1EA39E175; Thu, 18 Jun 2026 08:42:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781772125; cv=none; b=na/W0kH3u80Qq3d1HkyVtOCa5v18PkuZL6bvegKeAObzzWwpvzyc5SsOrRF2gueDYRLpfc43MFjlU89krC2K+tOrnjvfgdpxFSORtvwj6boUXCqJt8PvimJ+6X62CJicbulvpA62ldxsdMg1czEjgPndkiRC/nABvfozlizDEUg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781772125; c=relaxed/simple; bh=yRNRPBCUPQ0G3xv17DqJoRECg7OmRNWA0tUcK34RFvM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=DxFkDwtGgsLy+gHIHZk4fVCTPJD0QtrPwD0gd6syskkR0/M8C7kftoSNbQPWhsOZuDnreL9j1Q4r2hNCxUUCvWwajwLmsT0Pwn13z9qmYJEXud9jlA4wJRgWDheAs53xlra8yTC1R8SMU3aALQ05rDhgrJNLu4dUpWoZCsITS98= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Z7rxWD60; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Z7rxWD60" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 30C7A1F000E9; Thu, 18 Jun 2026 08:41:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781772124; bh=RKs9ir66i8mxyfauBkj7MGREb7nDkX7OxGexd1/PnhU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Z7rxWD60Q8cUSuDSV8lzscOFAMbL0aXmzN4C/T0nU7pITDihMCWBx9FFre95Xo+X+ 4fOejYcQmunAe12DyagZb+Ux+4MvZ8wNZVR4yLW/jP8L71G3jO4U04OzFgQz9eBVr6 lSUFxVDQaJ6LDiWOJHYZQ8uKdHMDf3qNLtfCqJbEYBbk4e41s9zk3Tq8Oc9HcTm4/6 FZBJU40l58xnf336bnytkrzP94T7P1UmYX1MAUOx1Pr2CbNzUF3ZFlGoNOn1BcX53E h0QeRE3N98Rgx5wo5JRT4WO8QawcVu1i2oWksGP3aa1j0diN4RlKKFTRFmsHmeqm0Q h7J85TSO2JKwQ== Message-ID: <38578aea-61c3-4328-aee9-8e7421672647@kernel.org> Date: Thu, 18 Jun 2026 10:41:59 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] cgroup/cpuset: rebind mm mempolicy to effective_mems, not mems_allowed To: Waiman Long , Gregory Price Cc: Farhad Alemi , Andrew Morton , Farhad Alemi , Yury Norov , Joshua Hahn , Zi Yan , Matthew Brost , Rakie Kim , Byungchul Park , Ying Huang , Alistair Popple , Rasmus Villemoes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, stable@vger.kernel.org References: <8d3b4561-92cd-4ebc-8462-5fb0fd659e8a@kernel.org> <70f486ce-5ef6-4d72-8cc3-7086f4eea930@redhat.com> <51eafe6c-6622-479b-b391-6d3ff9350e75@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 6/16/26 17:23, Waiman Long wrote: > On 6/16/26 2:59 AM, David Hildenbrand (Arm) wrote: >> On 6/16/26 05:43, Waiman Long wrote: >>> BTW, I still prefer the v2 patch. If it is decided we should use the >>> guarantee_online_mems() value instead, it will have to be a separate patch with >>> changes in the relevant documentation like Documentation/admin-guide/cgroup-v1/ >>> cpuset.rst. >> newmems is "obviously" correct, so I really don't see why we should add >> something that needs half a page of text to explain why it is fine -- if newmems >> just does the trick? >> >> Please enlighten me. > > Yes, taking newmems is a reasonable choice and there are pros and cons with each > options. My focus is more on not changing how v1 cpuset behaves as it is well > defined in the v1 cpusets.rst file: > >     Requests by a task, using the sched_setaffinity(2) system call to >     include CPUs in its CPU affinity mask, and using the mbind(2) and >     set_mempolicy(2) system calls to include Memory Nodes in its memory >     policy, are both filtered through that task's cpuset, filtering out any >     CPUs or Memory Nodes not in that cpuset.  The scheduler will not >     schedule a task on a CPU that is not allowed in its cpus_allowed >     vector, and the kernel page allocator will not allocate a page on a >     node that is not allowed in the requesting task's mems_allowed vector. > > v2, OTOH, is more vague as to what setting cpuset.mems will mean and we > generally follow what v1 is doing, but we have more leeway of what we can do. > > Using newmems will make the above text not totally correct. At least the offline > memory nodes will be filtered out which will not be utilized by the task when > the offline node becomes online. That is why I am saying that we will have to > correct the documentation if we want to make this change. So IIUC: diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 1335e437098e..cdfc615f35a5 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -2645,7 +2645,13 @@ void cpuset_update_tasks_nodemask(struct cpuset *cs) migrate = is_memory_migrate(cs); - mpol_rebind_mm(mm, &cs->mems_allowed); + /* + * For v1 we can have empty effective_mems, but we cannot + * attach any tasks (see cpuset_can_attach_check()). For v2, + * it's guaranteed to not be empty. + */ + VM_WARN_ON_ONCE(nodes_empty(cs->effective_mems)); + mpol_rebind_mm(mm, &cs->effective_mems); if (migrate) cpuset_migrate_mm(mm, &cs->old_mems_allowed, &newmems); else -- Cheers, David