From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-178.mta1.migadu.com (out-178.mta1.migadu.com [95.215.58.178]) (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 DF2FD3E5A3F for ; Tue, 2 Jun 2026 13:37:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780407449; cv=none; b=NP8JQgGj0GH5uknRWoFneq7Tmp+GbuZVd3Gooi0gBch+CAS+gCy90GFxfNr9MUu4pgQq8VlN918xbOuRh3YMexKSq8bc9BnIqByRuMPZ38j7uZLpm26Sf6h6ePd/VtUlKVZOSmVfHoHD34QN7XCrJGwAtVQzjzeGQ+lqbTHbkeU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780407449; c=relaxed/simple; bh=opT1djNuF0VQTOD8YZ4vL8EPRbIrVANLjmqGMG7W6R0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qRHySw4TsOhAbgckf5dX4uB9YDjJ7l5xwAAV/CpxCHuO0fnULSJ18smRcM70G/xIsBdu3gWanMF9j6oLgSUH6DUIA8IzXVPIYbI39xl2lAJ12sZVPp1GMRDvhNbF/+O2yoSN58nhSE0feL3dyoPpUUJp1SlVozKkHamral/v5M4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=eAowQ8oM; arc=none smtp.client-ip=95.215.58.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="eAowQ8oM" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1780407444; 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=PY5Ix0GcJYEWXHg8qof86Ez84D7zG6nfT1VsEVNpKkE=; b=eAowQ8oMEord+v7B6ndgqldDNO+pwh08G9I98czU6yG1X4SMNWMZovIf/A9t9qdfMoyj+a 3EggxNwPsw2m76HOtRP4GUG8A4Gn1HrOJ1TpDG7MZwiv5vVhUqHSVWWx/l2wj8rMuybiGT XqxUO4yMIhSKy7QQiYAio2824+bVirM= Date: Tue, 2 Jun 2026 21:37:07 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH-next v5 1/6] cgroup/cpuset: Fix node inconsistencies between cpuset_update_tasks_nodemask() and cpuset_attach() To: Waiman Long , Tejun Heo , Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Peter Zijlstra , ridong.chen@linux.dev 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 X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Ridong Chen In-Reply-To: <20260602023203.248077-2-longman@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT 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); } ``` > 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? > 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 -- Best regards, Ridong