linux-kernel - [PATCH] smpboot: dynamically allocate the cpumask

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Date:	Fri, 1 May 2015 16:00:47 -0400
From:	Chris Metcalf <cmetcalf@...hip.com>
To:	Frederic Weisbecker <fweisbec@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Peter Zijlstra" <peterz@...radead.org>,
	<linux-kernel@...r.kernel.org>
CC:	Chris Metcalf <cmetcalf@...hip.com>
Subject: [PATCH] smpboot: dynamically allocate the cpumask

Frederic Weisbecker observed that we'd be better off to dynamically
allocate the cpumask associated with smpboot threads to save memory.

Signed-off-by: Chris Metcalf <cmetcalf@...hip.com>
---
(Dropped a bunch of people off the cc's)

I figured since Andrew had already taken the previous v10 patchset into
the -mm tree, it was better to just submit this as a followup patch.
I can also argue that since it doesn't fix a bug per se, just improves
memory usage, it seems OK to have as a follow-on patch.

That said, I can respin a v11 patch 1/3 instead to give a new single
patch for smpboot; Andrew, just let me know if you'd prefer that.

 include/linux/smpboot.h |  2 +-
 kernel/smpboot.c        | 12 ++++++++----
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/include/linux/smpboot.h b/include/linux/smpboot.h
index 7c42153edfac..da3c593f9845 100644
--- a/include/linux/smpboot.h
+++ b/include/linux/smpboot.h
@@ -43,7 +43,7 @@ struct smp_hotplug_thread {
 	void				(*park)(unsigned int cpu);
 	void				(*unpark)(unsigned int cpu);
 	void				(*pre_unpark)(unsigned int cpu);
-	struct cpumask			cpumask;
+	cpumask_var_t			cpumask;
 	bool				selfparking;
 	const char			*thread_comm;
 };
diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index 209750ab7031..5e46c2a75d59 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -232,7 +232,7 @@ void smpboot_unpark_threads(unsigned int cpu)
 
 	mutex_lock(&smpboot_threads_lock);
 	list_for_each_entry(cur, &hotplug_threads, list)
-		if (cpumask_test_cpu(cpu, &cur->cpumask))
+		if (cpumask_test_cpu(cpu, cur->cpumask))
 			smpboot_unpark_thread(cur, cpu);
 	mutex_unlock(&smpboot_threads_lock);
 }
@@ -260,7 +260,7 @@ static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
 	unsigned int cpu;
 
 	/* Unpark any threads that were voluntarily parked. */
-	for_each_cpu_not(cpu, &ht->cpumask) {
+	for_each_cpu_not(cpu, ht->cpumask) {
 		if (cpu_online(cpu)) {
 			struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
 			if (tsk)
@@ -291,7 +291,10 @@ int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
 	unsigned int cpu;
 	int ret = 0;
 
-	cpumask_copy(&plug_thread->cpumask, cpu_possible_mask);
+	if (!alloc_cpumask_var(&plug_thread->cpumask, GFP_KERNEL))
+		return -ENOMEM;
+	cpumask_copy(plug_thread->cpumask, cpu_possible_mask);
+
 	get_online_cpus();
 	mutex_lock(&smpboot_threads_lock);
 	for_each_online_cpu(cpu) {
@@ -324,6 +327,7 @@ void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
 	smpboot_destroy_threads(plug_thread);
 	mutex_unlock(&smpboot_threads_lock);
 	put_online_cpus();
+	free_cpumask_var(plug_thread->cpumask);
 }
 EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
 
@@ -338,7 +342,7 @@ EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
 int smpboot_update_cpumask_percpu_thread(struct smp_hotplug_thread *plug_thread,
 					 const struct cpumask *new)
 {
-	struct cpumask *old = &plug_thread->cpumask;
+	struct cpumask *old = plug_thread->cpumask;
 	cpumask_var_t tmp;
 	unsigned int cpu;
 
-- 
2.1.2

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