[PATCH] smpboot: dynamically allocate the cpumask

Chris Metcalf
2015-05-01T20:01:03Z

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@ezchip.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