[PATCH RT 08/11] mm: perform lru_add_drain_all() remotely

Steven Rostedt
2016-07-12T16:53:20Z

[-- Attachment #1: 0008-mm-perform-lru_add_drain_all-remotely.patch --]
[-- Type: text/plain, Size: 3192 bytes --]

3.12.61-rt82-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Luiz Capitulino <lcapitulino@redhat.com>

lru_add_drain_all() works by scheduling lru_add_drain_cpu() to run
on all CPUs that have non-empty LRU pagevecs and then waiting for
the scheduled work to complete. However, workqueue threads may never
have the chance to run on a CPU that's running a SCHED_FIFO task.
This causes lru_add_drain_all() to block forever.

This commit solves this problem by changing lru_add_drain_all()
to drain the LRU pagevecs of remote CPUs. This is done by grabbing
swapvec_lock and calling lru_add_drain_cpu().

PS: This is based on an idea and initial implementation by
Rik van Riel.

Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
mm/swap.c | 37 ++++++++++++++++++++++++++++++-------
1 file changed, 30 insertions(+), 7 deletions(-)

diff --git a/mm/swap.c b/mm/swap.c
index 8ab73ba62a68..05e75d61c707 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -718,9 +718,15 @@ void lru_add_drain_cpu(int cpu)
unsigned long flags;

/* No harm done if a racing interrupt already did this */
+#ifdef CONFIG_PREEMPT_RT_BASE
+ local_lock_irqsave_on(rotate_lock, flags, cpu);
+ pagevec_move_tail(pvec);
+ local_unlock_irqrestore_on(rotate_lock, flags, cpu);
+#else
local_lock_irqsave(rotate_lock, flags);
pagevec_move_tail(pvec);
local_unlock_irqrestore(rotate_lock, flags);
+#endif
}

pvec = &per_cpu(lru_deactivate_pvecs, cpu);
@@ -763,12 +769,32 @@ void lru_add_drain(void)
local_unlock_cpu(swapvec_lock);
}

+
+#ifdef CONFIG_PREEMPT_RT_BASE
+static inline void remote_lru_add_drain(int cpu, struct cpumask *has_work)
+{
+ local_lock_on(swapvec_lock, cpu);
+ lru_add_drain_cpu(cpu);
+ local_unlock_on(swapvec_lock, cpu);
+}
+
+#else
+
static void lru_add_drain_per_cpu(struct work_struct *dummy)
{
lru_add_drain();
}

static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);
+static inline void remote_lru_add_drain(int cpu, struct cpumask *has_work)
+{
+ struct work_struct *work = &per_cpu(lru_add_drain_work, cpu);
+
+ INIT_WORK(work, lru_add_drain_per_cpu);
+ schedule_work_on(cpu, work);
+ cpumask_set_cpu(cpu, has_work);
+}
+#endif

void lru_add_drain_all(void)
{
@@ -781,20 +807,17 @@ void lru_add_drain_all(void)
cpumask_clear(&has_work);

for_each_online_cpu(cpu) {
- struct work_struct *work = &per_cpu(lru_add_drain_work, cpu);
-
if (pagevec_count(&per_cpu(lru_add_pvec, cpu)) ||
pagevec_count(&per_cpu(lru_rotate_pvecs, cpu)) ||
pagevec_count(&per_cpu(lru_deactivate_pvecs, cpu)) ||
- need_activate_page_drain(cpu)) {
- INIT_WORK(work, lru_add_drain_per_cpu);
- schedule_work_on(cpu, work);
- cpumask_set_cpu(cpu, &has_work);
- }
+ need_activate_page_drain(cpu))
+ remote_lru_add_drain(cpu, &has_work);
}

+#ifndef CONFIG_PREEMPT_RT_BASE
for_each_cpu(cpu, &has_work)
flush_work(&per_cpu(lru_add_drain_work, cpu));
+#endif

put_online_cpus();
mutex_unlock(&lock);
--
2.8.1