Message-ID: <20260108203755.1163107-5-gourry@gourry.net>
Date: Thu,  8 Jan 2026 15:37:51 -0500
From: Gregory Price <gourry@...rry.net>
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Subject: [RFC PATCH v3 4/8] cpuset: introduce cpuset.mems.sysram

mems_sysram contains only SystemRAM nodes (omitting Private Nodes).

The nodemask is intersect(effective_mems, node_states[N_MEMORY]).

When checking mems_allowed, check for __GFP_THISNODE to determine if
the check should be made against sysram_nodes or mems_allowed.

This omits Private Nodes (N_PRIVATE) from default mems_allowed checks,
making those nodes unreachable via normal allocation paths (page
faults, mempolicies, etc).

Signed-off-by: Gregory Price <gourry@...rry.net>
---
 include/linux/cpuset.h          | 20 +++++--
 kernel/cgroup/cpuset-internal.h |  8 +++
 kernel/cgroup/cpuset-v1.c       |  8 +++
 kernel/cgroup/cpuset.c          | 96 +++++++++++++++++++++++++--------
 mm/memcontrol.c                 |  2 +-
 mm/mempolicy.c                  |  6 +--
 mm/migrate.c                    |  4 +-
 7 files changed, 112 insertions(+), 32 deletions(-)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index fe4f29624117..1ae09ec0fcb7 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -174,7 +174,9 @@ static inline void set_mems_allowed(nodemask_t nodemask)
 	task_unlock(current);
 }
 
-extern void cpuset_nodes_allowed(struct cgroup *cgroup, nodemask_t *mask);
+extern void cpuset_sysram_nodes_allowed(struct cgroup *cgroup,
+					nodemask_t *mask);
+extern nodemask_t cpuset_sysram_nodemask(struct task_struct *p);
 #else /* !CONFIG_CPUSETS */
 
 static inline bool cpusets_enabled(void) { return false; }
@@ -218,7 +220,13 @@ static inline bool cpuset_cpu_is_isolated(int cpu)
 	return false;
 }
 
-static inline nodemask_t cpuset_mems_allowed(struct task_struct *p)
+static inline void cpuset_sysram_nodes_allowed(struct cgroup *cgroup,
+					       nodemask_t *mask)
+{
+	nodes_copy(*mask, node_possible_map);
+}
+
+static inline nodemask_t cpuset_sysram_nodemask(struct task_struct *p)
 {
 	return node_possible_map;
 }
@@ -301,10 +309,16 @@ static inline bool read_mems_allowed_retry(unsigned int seq)
 	return false;
 }
 
-static inline void cpuset_nodes_allowed(struct cgroup *cgroup, nodemask_t *mask)
+static inline void cpuset_sysram_nodes_allowed(struct cgroup *cgroup,
+					       nodemask_t *mask)
 {
 	nodes_copy(*mask, node_states[N_MEMORY]);
 }
+
+static nodemask_t cpuset_sysram_nodemask(struct task_struct *p)
+{
+	return node_states[N_MEMORY];
+}
 #endif /* !CONFIG_CPUSETS */
 
 #endif /* _LINUX_CPUSET_H */
diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h
index 01976c8e7d49..4764aaef585f 100644
--- a/kernel/cgroup/cpuset-internal.h
+++ b/kernel/cgroup/cpuset-internal.h
@@ -53,6 +53,7 @@ typedef enum {
 	FILE_MEMORY_MIGRATE,
 	FILE_CPULIST,
 	FILE_MEMLIST,
+	FILE_MEMS_SYSRAM,
 	FILE_EFFECTIVE_CPULIST,
 	FILE_EFFECTIVE_MEMLIST,
 	FILE_SUBPARTS_CPULIST,
@@ -104,6 +105,13 @@ struct cpuset {
 	cpumask_var_t effective_cpus;
 	nodemask_t effective_mems;
 
+	/*
+	 * SystemRAM Memory Nodes for tasks.
+	 * This is the intersection of effective_mems and node_states[N_MEMORY].
+	 * Tasks will have their sysram_nodes set to this value.
+	 */
+	nodemask_t mems_sysram;
+
 	/*
 	 * Exclusive CPUs dedicated to current cgroup (default hierarchy only)
 	 *
diff --git a/kernel/cgroup/cpuset-v1.c b/kernel/cgroup/cpuset-v1.c
index 12e76774c75b..45b74181effd 100644
--- a/kernel/cgroup/cpuset-v1.c
+++ b/kernel/cgroup/cpuset-v1.c
@@ -293,6 +293,8 @@ void cpuset1_hotplug_update_tasks(struct cpuset *cs,
 	cpumask_copy(cs->effective_cpus, new_cpus);
 	cs->mems_allowed = *new_mems;
 	cs->effective_mems = *new_mems;
+	nodes_and(cs->mems_sysram, cs->effective_mems, node_states[N_MEMORY]);
+	cpuset_update_tasks_nodemask(cs);
 	cpuset_callback_unlock_irq();
 
 	/*
@@ -532,6 +534,12 @@ struct cftype cpuset1_files[] = {
 		.private = FILE_EFFECTIVE_MEMLIST,
 	},
 
+	{
+		.name = "mems_sysram",
+		.seq_show = cpuset_common_seq_show,
+		.private = FILE_MEMS_SYSRAM,
+	},
+
 	{
 		.name = "cpu_exclusive",
 		.read_u64 = cpuset_read_u64,
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index a3ade9d5968b..4c213a2ea7ac 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -29,6 +29,7 @@
 #include <linux/mempolicy.h>
 #include <linux/mm.h>
 #include <linux/memory.h>
+#include <linux/memory-tiers.h>
 #include <linux/export.h>
 #include <linux/rcupdate.h>
 #include <linux/sched.h>
@@ -454,11 +455,11 @@ static void guarantee_active_cpus(struct task_struct *tsk,
  *
  * Call with callback_lock or cpuset_mutex held.
  */
-static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
+static void guarantee_online_sysram_nodes(struct cpuset *cs, nodemask_t *pmask)
 {
-	while (!nodes_intersects(cs->effective_mems, node_states[N_MEMORY]))
+	while (!nodes_intersects(cs->mems_sysram, node_states[N_MEMORY]))
 		cs = parent_cs(cs);
-	nodes_and(*pmask, cs->effective_mems, node_states[N_MEMORY]);
+	nodes_and(*pmask, cs->mems_sysram, node_states[N_MEMORY]);
 }
 
 /**
@@ -2791,7 +2792,7 @@ void cpuset_update_tasks_nodemask(struct cpuset *cs)
 
 	cpuset_being_rebound = cs;		/* causes mpol_dup() rebind */
 
-	guarantee_online_mems(cs, &newmems);
+	guarantee_online_sysram_nodes(cs, &newmems);
 
 	/*
 	 * The mpol_rebind_mm() call takes mmap_lock, which we couldn't
@@ -2816,7 +2817,7 @@ 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->mems_sysram);
 		if (migrate)
 			cpuset_migrate_mm(mm, &cs->old_mems_allowed, &newmems);
 		else
@@ -2876,6 +2877,8 @@ static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems)
 
 		spin_lock_irq(&callback_lock);
 		cp->effective_mems = *new_mems;
+		nodes_and(cp->mems_sysram, cp->effective_mems,
+			  node_states[N_MEMORY]);
 		spin_unlock_irq(&callback_lock);
 
 		WARN_ON(!is_in_v2_mode() &&
@@ -3304,11 +3307,11 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 	 * by skipping the task iteration and update.
 	 */
 	if (cpuset_v2() && !cpus_updated && !mems_updated) {
-		cpuset_attach_nodemask_to = cs->effective_mems;
+		cpuset_attach_nodemask_to = cs->mems_sysram;
 		goto out;
 	}
 
-	guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
+	guarantee_online_sysram_nodes(cs, &cpuset_attach_nodemask_to);
 
 	cgroup_taskset_for_each(task, css, tset)
 		cpuset_attach_task(cs, task);
@@ -3319,7 +3322,7 @@ 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;
+	cpuset_attach_nodemask_to = cs->mems_sysram;
 	if (!is_memory_migrate(cs) && !mems_updated)
 		goto out;
 
@@ -3441,6 +3444,9 @@ int cpuset_common_seq_show(struct seq_file *sf, void *v)
 	case FILE_EFFECTIVE_MEMLIST:
 		seq_printf(sf, "%*pbl\n", nodemask_pr_args(&cs->effective_mems));
 		break;
+	case FILE_MEMS_SYSRAM:
+		seq_printf(sf, "%*pbl\n", nodemask_pr_args(&cs->mems_sysram));
+		break;
 	case FILE_EXCLUSIVE_CPULIST:
 		seq_printf(sf, "%*pbl\n", cpumask_pr_args(cs->exclusive_cpus));
 		break;
@@ -3552,6 +3558,12 @@ static struct cftype dfl_files[] = {
 		.private = FILE_EFFECTIVE_MEMLIST,
 	},
 
+	{
+		.name = "mems.sysram",
+		.seq_show = cpuset_common_seq_show,
+		.private = FILE_MEMS_SYSRAM,
+	},
+
 	{
 		.name = "cpus.partition",
 		.seq_show = cpuset_partition_show,
@@ -3654,6 +3666,8 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
 	if (is_in_v2_mode()) {
 		cpumask_copy(cs->effective_cpus, parent->effective_cpus);
 		cs->effective_mems = parent->effective_mems;
+		nodes_and(cs->mems_sysram, cs->effective_mems,
+			  node_states[N_MEMORY]);
 	}
 	spin_unlock_irq(&callback_lock);
 
@@ -3685,6 +3699,8 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
 	spin_lock_irq(&callback_lock);
 	cs->mems_allowed = parent->mems_allowed;
 	cs->effective_mems = parent->mems_allowed;
+	nodes_and(cs->mems_sysram, cs->effective_mems,
+		  node_states[N_MEMORY]);
 	cpumask_copy(cs->cpus_allowed, parent->cpus_allowed);
 	cpumask_copy(cs->effective_cpus, parent->cpus_allowed);
 	spin_unlock_irq(&callback_lock);
@@ -3838,7 +3854,7 @@ static void cpuset_fork(struct task_struct *task)
 
 	/* CLONE_INTO_CGROUP */
 	mutex_lock(&cpuset_mutex);
-	guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
+	guarantee_online_sysram_nodes(cs, &cpuset_attach_nodemask_to);
 	cpuset_attach_task(cs, task);
 
 	dec_attach_in_progress_locked(cs);
@@ -3887,7 +3903,8 @@ int __init cpuset_init(void)
 	cpumask_setall(top_cpuset.effective_xcpus);
 	cpumask_setall(top_cpuset.exclusive_cpus);
 	nodes_setall(top_cpuset.effective_mems);
-
+	nodes_and(top_cpuset.mems_sysram, top_cpuset.effective_mems,
+		  node_states[N_MEMORY]);
 	fmeter_init(&top_cpuset.fmeter);
 
 	BUG_ON(!alloc_cpumask_var(&cpus_attach, GFP_KERNEL));
@@ -3916,6 +3933,7 @@ hotplug_update_tasks(struct cpuset *cs,
 	spin_lock_irq(&callback_lock);
 	cpumask_copy(cs->effective_cpus, new_cpus);
 	cs->effective_mems = *new_mems;
+	nodes_and(cs->mems_sysram, cs->effective_mems, node_states[N_MEMORY]);
 	spin_unlock_irq(&callback_lock);
 
 	if (cpus_updated)
@@ -4064,7 +4082,15 @@ static void cpuset_handle_hotplug(void)
 
 	/* fetch the available cpus/mems and find out which changed how */
 	cpumask_copy(&new_cpus, cpu_active_mask);
-	new_mems = node_states[N_MEMORY];
+
+	/*
+	 * Effective mems is union(N_MEMORY, N_PRIVATE), this allows
+	 * control over N_PRIVATE node usage from cgroups while
+	 * mems.sysram prevents N_PRIVATE nodes from being used
+	 * without __GFP_THISNODE.
+	 */
+	nodes_clear(new_mems);
+	nodes_or(new_mems, node_states[N_MEMORY], node_states[N_PRIVATE]);
 
 	/*
 	 * If subpartitions_cpus is populated, it is likely that the check
@@ -4106,6 +4132,8 @@ static void cpuset_handle_hotplug(void)
 		if (!on_dfl)
 			top_cpuset.mems_allowed = new_mems;
 		top_cpuset.effective_mems = new_mems;
+		nodes_and(top_cpuset.mems_sysram, top_cpuset.effective_mems,
+			  node_states[N_MEMORY]);
 		spin_unlock_irq(&callback_lock);
 		cpuset_update_tasks_nodemask(&top_cpuset);
 	}
@@ -4176,6 +4204,7 @@ void __init cpuset_init_smp(void)
 
 	cpumask_copy(top_cpuset.effective_cpus, cpu_active_mask);
 	top_cpuset.effective_mems = node_states[N_MEMORY];
+	top_cpuset.mems_sysram = node_states[N_MEMORY];
 
 	hotplug_node_notifier(cpuset_track_online_nodes, CPUSET_CALLBACK_PRI);
 
@@ -4293,14 +4322,18 @@ bool cpuset_cpus_allowed_fallback(struct task_struct *tsk)
 	return changed;
 }
 
+/*
+ * At this point in time, no hotplug nodes can have been added, so just set
+ * the sysram_nodes of the init task to the set of N_MEMORY nodes.
+ */
 void __init cpuset_init_current_mems_allowed(void)
 {
-	nodes_setall(current->mems_allowed);
+	current->mems_allowed = node_states[N_MEMORY];
 }
 
 /**
- * cpuset_mems_allowed - return mems_allowed mask from a tasks cpuset.
- * @tsk: pointer to task_struct from which to obtain cpuset->mems_allowed.
+ * cpuset_sysram_nodemask - return mems_sysram mask from a tasks cpuset.
+ * @tsk: pointer to task_struct from which to obtain cpuset->mems_sysram.
  *
  * Description: Returns the nodemask_t mems_allowed of the cpuset
  * attached to the specified @tsk.  Guaranteed to return some non-empty
@@ -4308,13 +4341,13 @@ void __init cpuset_init_current_mems_allowed(void)
  * tasks cpuset.
  **/
 
-nodemask_t cpuset_mems_allowed(struct task_struct *tsk)
+nodemask_t cpuset_sysram_nodemask(struct task_struct *tsk)
 {
 	nodemask_t mask;
 	unsigned long flags;
 
 	spin_lock_irqsave(&callback_lock, flags);
-	guarantee_online_mems(task_cs(tsk), &mask);
+	guarantee_online_sysram_nodes(task_cs(tsk), &mask);
 	spin_unlock_irqrestore(&callback_lock, flags);
 
 	return mask;
@@ -4383,17 +4416,30 @@ static struct cpuset *nearest_hardwall_ancestor(struct cpuset *cs)
  *	tsk_is_oom_victim   - any node ok
  *	GFP_KERNEL   - any node in enclosing hardwalled cpuset ok
  *	GFP_USER     - only nodes in current tasks mems allowed ok.
+ *	GFP_THISNODE - allows private memory nodes in mems_allowed
  */
 bool cpuset_current_node_allowed(int node, gfp_t gfp_mask)
 {
 	struct cpuset *cs;		/* current cpuset ancestors */
 	bool allowed;			/* is allocation in zone z allowed? */
 	unsigned long flags;
+	bool private_nodes = gfp_mask & __GFP_THISNODE;
 
+	/* Only SysRAM nodes are valid in interrupt context */
 	if (in_interrupt())
-		return true;
-	if (node_isset(node, current->mems_allowed))
-		return true;
+		return node_isset(node, node_states[N_MEMORY]);
+
+	if (private_nodes) {
+		rcu_read_lock();
+		cs = task_cs(current);
+		allowed = node_isset(node, cs->effective_mems);
+		rcu_read_unlock();
+	} else
+		allowed = node_isset(node, current->mems_allowed);
+
+	if (allowed)
+		return allowed;
+
 	/*
 	 * Allow tasks that have access to memory reserves because they have
 	 * been OOM killed to get memory anywhere.
@@ -4412,6 +4458,10 @@ bool cpuset_current_node_allowed(int node, gfp_t gfp_mask)
 	cs = nearest_hardwall_ancestor(task_cs(current));
 	allowed = node_isset(node, cs->mems_allowed);
 
+	/* If not allowing private node allocation, restrict to sysram nodes */
+	if (!private_nodes)
+		allowed &= node_isset(node, node_states[N_MEMORY]);
+
 	spin_unlock_irqrestore(&callback_lock, flags);
 	return allowed;
 }
@@ -4434,7 +4484,7 @@ bool cpuset_current_node_allowed(int node, gfp_t gfp_mask)
  * online due to hot plugins. Callers should check the mask for validity on
  * return based on its subsequent use.
  **/
-void cpuset_nodes_allowed(struct cgroup *cgroup, nodemask_t *mask)
+void cpuset_sysram_nodes_allowed(struct cgroup *cgroup, nodemask_t *mask)
 {
 	struct cgroup_subsys_state *css;
 	struct cpuset *cs;
@@ -4457,16 +4507,16 @@ void cpuset_nodes_allowed(struct cgroup *cgroup, nodemask_t *mask)
 
 	/*
 	 * The reference taken via cgroup_get_e_css is sufficient to
-	 * protect css, but it does not imply safe accesses to effective_mems.
+	 * protect css, but it does not imply safe accesses to mems_sysram.
 	 *
-	 * Normally, accessing effective_mems would require the cpuset_mutex
+	 * Normally, accessing mems_sysram would require the cpuset_mutex
 	 * or callback_lock - but the correctness of this information is stale
 	 * immediately after the query anyway. We do not acquire the lock
 	 * during this process to save lock contention in exchange for racing
 	 * against mems_allowed rebinds.
 	 */
 	cs = container_of(css, struct cpuset, css);
-	nodes_copy(*mask, cs->effective_mems);
+	nodes_copy(*mask, cs->mems_sysram);
 	css_put(css);
 }
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7fbe9565cd06..2df7168edca0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5610,7 +5610,7 @@ void mem_cgroup_node_filter_allowed(struct mem_cgroup *memcg, nodemask_t *mask)
 	 * in effective_mems and hot-unpluging of nodes, inaccurate allowed
 	 * mask is acceptable.
 	 */
-	cpuset_nodes_allowed(memcg->css.cgroup, &allowed);
+	cpuset_sysram_nodes_allowed(memcg->css.cgroup, &allowed);
 	nodes_and(*mask, *mask, allowed);
 }
 
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 76da50425712..760b5b6b4ae6 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1901,14 +1901,14 @@ static int kernel_migrate_pages(pid_t pid, unsigned long maxnode,
 	}
 	rcu_read_unlock();
 
-	task_nodes = cpuset_mems_allowed(task);
+	task_nodes = cpuset_sysram_nodemask(task);
 	/* Is the user allowed to access the target nodes? */
 	if (!nodes_subset(*new, task_nodes) && !capable(CAP_SYS_NICE)) {
 		err = -EPERM;
 		goto out_put;
 	}
 
-	task_nodes = cpuset_mems_allowed(current);
+	task_nodes = cpuset_sysram_nodemask(current);
 	nodes_and(*new, *new, task_nodes);
 	if (nodes_empty(*new))
 		goto out_put;
@@ -2833,7 +2833,7 @@ struct mempolicy *__mpol_dup(struct mempolicy *old)
 		*new = *old;
 
 	if (current_cpuset_is_being_rebound()) {
-		nodemask_t mems = cpuset_mems_allowed(current);
+		nodemask_t mems = cpuset_sysram_nodemask(current);
 		mpol_rebind_policy(new, &mems);
 	}
 	atomic_set(&new->refcnt, 1);
diff --git a/mm/migrate.c b/mm/migrate.c
index 5169f9717f60..0ad893bf862b 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2534,7 +2534,7 @@ static struct mm_struct *find_mm_struct(pid_t pid, nodemask_t *mem_nodes)
 	 */
 	if (!pid) {
 		mmget(current->mm);
-		*mem_nodes = cpuset_mems_allowed(current);
+		*mem_nodes = cpuset_sysram_nodemask(current);
 		return current->mm;
 	}
 
@@ -2555,7 +2555,7 @@ static struct mm_struct *find_mm_struct(pid_t pid, nodemask_t *mem_nodes)
 	mm = ERR_PTR(security_task_movememory(task));
 	if (IS_ERR(mm))
 		goto out;
-	*mem_nodes = cpuset_mems_allowed(task);
+	*mem_nodes = cpuset_sysram_nodemask(task);
 	mm = get_task_mm(task);
 out:
 	put_task_struct(task);
-- 
2.52.0

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