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 2D6E335F5ED; Mon, 22 Jun 2026 07:12:44 +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=1782112366; cv=none; b=qb6zTF3PRFEw/C7t/xm1n5mrue8F7mlW313pbIdpkmjt5O2S0Arm8OMFxfaPZUpySvCzbN+Dw+8eZAKMCUjUMsJ+3bYliFTGVGRr0lKGlpJH9g9iAU+Y7sg7Pg7p3Du/vdaW8XlKnbcekyWpghdiEFmGGLyt1tT9wkyjd1zG5Nk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782112366; c=relaxed/simple; bh=AGUF0YQ33EbwT/3ioHdkBECB1RdLPaf7AAogYZIJpVg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ZlJFJeRgL/BYxxAzE+FVYOy1+GOZDMVih0N2Rq6DZyP+8gtnn4xggTAOsiRdEQSQFeg5jaMtij7H4CUwK97Bwtp1s05JxXzwuOHvLriQIPS379Aagr/XWIfHkRfgay6Ae96yMl8ijrH9qWtq/mJw1PzhsAfBhjPQtpCpgCqklDE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=L4PNXIa9; 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="L4PNXIa9" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 83A371F000E9; Mon, 22 Jun 2026 07:12:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782112364; bh=JPDKWUY1v1INodMedwDx7DwR6GeDNvta1xVixbP8aME=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=L4PNXIa9Zw4w4w825y5AbRuIkOOgKjEMz0H/IY6pmo0/6ndTOJFPljNEwX3AL7dbj plw6zBxzTfQaZ/UroLuI54iZKHPFrPnF3lAqPwgK92ea6EP595egePsMrZLYbUJJoU 168UWkvIZs2O/Ux0HkhEJiGWOLIT53MX63q3eL8x0Hhha674hOrFnrSs35GDOW2/Lx CSSgZC2lV8LlJN/6+qpsxBWDeUwGAGbcZWTnr89VN2ut3cW8PKou1Rl9C1+nzzIlw5 6g7rbChB8u464k5hXQt7m1oerM34BEUDf/rr49Uy6trcC8HiyUQtylGI43wb1argWM rOa11sg/oUJ/w== Message-ID: Date: Mon, 22 Jun 2026 09:12:38 +0200 Precedence: bulk X-Mailing-List: cgroups@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> <38578aea-61c3-4328-aee9-8e7421672647@kernel.org> <9d8b650d-6faa-425a-8db7-1e206cb25158@redhat.com> 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 6/21/26 05:24, Waiman Long wrote: > On 6/18/26 4:41 AM, David Hildenbrand (Arm) wrote: >> On 6/16/26 17:23, Waiman Long wrote: >>> 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 > > That is true, but I don't think we need a VM_WARN_ON_ONCE() here. I'd prefer if we catch such stuff in the future more easily than running into late divide-by-zero. Maybe we should check in mpol_rebind_mm() instead. -- Cheers, David