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 7355C3909A4 for ; Tue, 2 Jun 2026 18:43:52 +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=1780425834; cv=none; b=QtLFZx4ajn02Yd2X/I57ktXCPcvfpSuLA7GQOPtQbEx0/6ELXNn1VBud8ZB89R2zM0RgN0MNf2ale7MUf655sdgFvvzKwN2HzhGVuHdLRIultdysqT8q0gQ12JuoIILXPiQpECLQ+7uJpsjymxHgD2c5wV4Kj/No00hAcTlZqGE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780425834; c=relaxed/simple; bh=zElxct/1WT2b2tunA3asgRCmTw4qu4z24mKu4YFjIZU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=nNBVgxunebZwdYbGgK/8Z2P1Bf1tdUWK+6e5QCxPp99Y2eLIYC3W4LX4RAAAT8aRYlj7oYwnHMShLNaplHlyIdjHl2/70eEsF8j4f4LMava5jOFApceDWLouyGW7aXcoHZUpDliaKR5e+L4T9X/+IAEm1X4cb1ff01K+4T8cDmc= 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=KUnT+G69; 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="KUnT+G69" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1780425831; 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=pt/RaQD8UDkqYaD1i19wIsnd5MdkfcYYg50zQvKOJS0=; b=KUnT+G69QTPu8xZ/lJ4nUfbjkp1ve84gEJxx5XzG7aPCzrbH/4UoBvcIKCruLg79BY5Y4D DZDmQxLU67jLZTm0ipTbdVn0kHaL2qLLNLHObCiwAJ+ypzlno9RBAUMyYILGdh9y8030NQ FRmG9iZ/V88WSMClxogacfcGAAfUEig= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-528-4n9xTPoDMvexAsgRHxX0zw-1; Tue, 02 Jun 2026 14:43:46 -0400 X-MC-Unique: 4n9xTPoDMvexAsgRHxX0zw-1 X-Mimecast-MFC-AGG-ID: 4n9xTPoDMvexAsgRHxX0zw_1780425823 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id DE4D51956079; Tue, 2 Jun 2026 18:43:41 +0000 (UTC) Received: from [10.22.80.32] (unknown [10.22.80.32]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 274B31800352; Tue, 2 Jun 2026 18:43:38 +0000 (UTC) Message-ID: <3f44a33e-dc4b-479c-9572-a02cacfc7af2@redhat.com> Date: Tue, 2 Jun 2026 14:43:38 -0400 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-next v5 1/6] cgroup/cpuset: Fix node inconsistencies between cpuset_update_tasks_nodemask() and cpuset_attach() To: Ridong Chen , Tejun Heo , Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Peter Zijlstra Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Aaron Tomlin , Guopeng Zhang References: <20260602023203.248077-1-longman@redhat.com> <20260602023203.248077-2-longman@redhat.com> Content-Language: en-US From: Waiman Long In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 On 6/2/26 9:37 AM, Ridong Chen wrote: > > On 2026/6/2 10:31, Waiman Long wrote: >> Whenever memory node mask is changed, there are 4 places where the node >> mask has to be updated or used. >> 1) task's node mask via cpuset_change_task_nodemask() >> 2) memory policy binding via mpol_rebind_mm() >> 3) if memory migration is enabled, migrate from old_mems_allowed to >> the new node mask via cpuset_migrate_mm(). >> 4) setting old_mems_allowed >> >> These memory actions are done in cpuset_update_tasks_nodemask() and >> cpuset_attach(). However there are inconsistencies in what node masks >> are being used in these 2 functions. >> >> In cpuset_update_tasks_nodemask(), >> - cpuset_change_task_nodemask(): guarantee_online_mems() >> - mpol_rebind_mm(): mems_allowed >> - cpuset_migrate_mm(): guarantee_online_mems() >> - old_mems_allowed: guarantee_online_mems() >> >> In cpuset_attach(), >> - cpuset_change_task_nodemask(): guarantee_online_mems() >> - mpol_rebind_mm(): effective_mems >> - cpuset_migrate_mm(): effective_mems >> - old_mems_allowed: effective_mems >> >> These inconsistencies dates back to quite a long time ago and it is >> hard to say what should be the correct values. >> >> The guarantee_online_mems() function returns a node mask from current or >> an ancestor cpuset that is a subset of node_states[N_MEMORY]. Nodes in >> node_states[N_MEMORY] are all online, i.e. in node_states[N_ONLINE]. >> However, node in node_states[N_ONLINE] may not have memory. So >> node_states[N_MEMORY] should be a subset of node_states[N_ONLINE]. >> >> The guarantee_online_mems() function should only be useful for v1 where >> mems_allowed is the same as effective_mems. With v2, the memory nodes >> in effective_mems should always be a subset of node_states[N_MEMORY]. >> The only time that may not be true is when a memory hot-unplug operation >> is in progress and a memory node is removed from node_states[N_MEMORY] >> but not yet reflected in effective_mems as cpuset_handle_hotplug() >> has not yet been called from cpuset_track_online_nodes(). When >> cpuset_handle_hotplug() is called later, the memory node setting >> of the relevant cpusets and tasks will be updated. So replacing the >> guarantee_online_mems() call by just using cs->effective_mems should >> be fine. >> > I noticed this pattern in several places: > > ``` > if (cpuset_v2()) > newmems = cs->effective_mems; > else > guarantee_online_mems(cs, &newmems); > ``` > > Would it be simpler to move the v2 logic into guarantee_online_mems? > > ``` > static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask) > { > if (cpuset_v2()) { > *pmask = cs->effective_mems; > return; > } > while (!nodes_and(*pmask, cs->effective_mems, node_states[N_MEMORY])) > cs = parent_cs(cs); > } > ``` Yes, it makes sense to put it directly into guarantee_online_mems(). >> Let use the following setup for both of them and make them consistent. >> - cpuset_change_task_nodemask(): guarantee_online_mems() >> - mpol_rebind_mm(): effective_mems >> - cpuset_migrate_mm(): guarantee_online_mems() >> - old_mems_allowed: guarantee_online_mems() >> >> So for v2, it is effectively all effective_mems. For v1, mpol_rebind_mm() >> uses cpus_allowed which may differ from what guarantee_online_mems() > ^ > mems_allowed? Thanks for catching it. Will fix that and update your email address in the next version. Cheers, Longman >> returns. >> >> Signed-off-by: Waiman Long >> --- >> kernel/cgroup/cpuset.c | 32 +++++++++++++++++++++----------- >> 1 file changed, 21 insertions(+), 11 deletions(-) >> >> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c >> index 6bdb68689c24..987456b6d879 100644 >> --- a/kernel/cgroup/cpuset.c >> +++ b/kernel/cgroup/cpuset.c >> @@ -2616,6 +2616,13 @@ static void *cpuset_being_rebound; >> * Iterate through each task of @cs updating its mems_allowed to the >> * effective cpuset's. As this function is called with cpuset_mutex held, >> * cpuset membership stays stable. >> + * >> + * - cpuset_change_task_nodemask(): guarantee_online_mems() >> + * - mpol_rebind_mm(): effective_mems >> + * - cpuset_migrate_mm(): guarantee_online_mems() >> + * - old_mems_allowed: guarantee_online_mems() >> + * >> + * For v2, guarantee_online_mems() should just return effective_mems. > I agree, but the implementation is not as simple as what I mentioned above. > >> */ >> void cpuset_update_tasks_nodemask(struct cpuset *cs) >> { >> @@ -2625,7 +2632,10 @@ void cpuset_update_tasks_nodemask(struct cpuset *cs) >> >> cpuset_being_rebound = cs; /* causes mpol_dup() rebind */ >> >> - guarantee_online_mems(cs, &newmems); >> + if (cpuset_v2()) >> + newmems = cs->effective_mems; >> + else >> + guarantee_online_mems(cs, &newmems); >> >> /* >> * The mpol_rebind_mm() call takes mmap_lock, which we couldn't >> @@ -2650,7 +2660,7 @@ void cpuset_update_tasks_nodemask(struct cpuset *cs) >> >> migrate = is_memory_migrate(cs); >> >> - mpol_rebind_mm(mm, &cs->mems_allowed); >> + mpol_rebind_mm(mm, &cs->effective_mems); >> if (migrate) >> cpuset_migrate_mm(mm, &cs->old_mems_allowed, &newmems); >> else >> @@ -3148,17 +3158,18 @@ static void cpuset_attach(struct cgroup_taskset *tset) >> >> /* >> * In the default hierarchy, enabling cpuset in the child cgroups >> - * will trigger a number of cpuset_attach() calls with no change >> - * in effective cpus and mems. In that case, we can optimize out >> - * by skipping the task iteration and update. >> + * will trigger a cpuset_attach() call with no change in effective cpus >> + * and mems. In that case, we can optimize out by skipping the task >> + * iteration and update. >> */ >> - if (cpuset_v2() && !cpus_updated && !mems_updated) { >> + if (cpuset_v2()) { >> cpuset_attach_nodemask_to = cs->effective_mems; >> - goto out; >> + if (!cpus_updated && !mems_updated) >> + goto out; >> + } else { >> + guarantee_online_mems(cs, &cpuset_attach_nodemask_to); >> } >> >> - guarantee_online_mems(cs, &cpuset_attach_nodemask_to); >> - >> cgroup_taskset_for_each(task, css, tset) >> cpuset_attach_task(cs, task); >> >> @@ -3168,7 +3179,6 @@ static void cpuset_attach(struct cgroup_taskset *tset) >> * if there is no change in effective_mems and CS_MEMORY_MIGRATE is >> * not set. >> */ >> - cpuset_attach_nodemask_to = cs->effective_mems; >> if (!is_memory_migrate(cs) && !mems_updated) >> goto out; >> >> @@ -3176,7 +3186,7 @@ static void cpuset_attach(struct cgroup_taskset *tset) >> struct mm_struct *mm = get_task_mm(leader); >> >> if (mm) { >> - mpol_rebind_mm(mm, &cpuset_attach_nodemask_to); >> + mpol_rebind_mm(mm, &cs->effective_mems); >> >> /* >> * old_mems_allowed is the same with mems_allowed