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Subject[PATCH v2] mm: make lru_add_drain_all() selective
This change makes lru_add_drain_all() only selectively interrupt
the cpus that have per-cpu free pages that can be drained.

This is important in nohz mode where calling mlockall(), for
example, otherwise will interrupt every core unnecessarily.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
---
Oops! In the previous version of this change I had just blindly patched
it forward from a slightly older version of mm/swap.c. This version is
now properly against a version of mm/swap.c that includes all the latest
changes to lru_add_drain_all().

include/linux/workqueue.h | 3 +++
kernel/workqueue.c | 35 ++++++++++++++++++++++++++---------
mm/swap.c | 37 ++++++++++++++++++++++++++++++++++++-
3 files changed, 65 insertions(+), 10 deletions(-)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index a0ed78a..71a3fe7 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -13,6 +13,8 @@
#include <linux/atomic.h>
#include <linux/cpumask.h>

+struct cpumask;
+
struct workqueue_struct;

struct work_struct;
@@ -470,6 +472,7 @@ extern void flush_workqueue(struct workqueue_struct *wq);
extern void drain_workqueue(struct workqueue_struct *wq);
extern void flush_scheduled_work(void);

+extern int schedule_on_cpu_mask(work_func_t func, const struct cpumask *mask);
extern int schedule_on_each_cpu(work_func_t func);

int execute_in_process_context(work_func_t fn, struct execute_work *);
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index f02c4a4..a6d1809 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2962,17 +2962,18 @@ bool cancel_delayed_work_sync(struct delayed_work *dwork)
EXPORT_SYMBOL(cancel_delayed_work_sync);

/**
- * schedule_on_each_cpu - execute a function synchronously on each online CPU
+ * schedule_on_cpu_mask - execute a function synchronously on each listed CPU
* @func: the function to call
+ * @mask: the cpumask to invoke the function on
*
- * schedule_on_each_cpu() executes @func on each online CPU using the
+ * schedule_on_cpu_mask() executes @func on each listed CPU using the
* system workqueue and blocks until all CPUs have completed.
- * schedule_on_each_cpu() is very slow.
+ * schedule_on_cpu_mask() is very slow.
*
* RETURNS:
* 0 on success, -errno on failure.
*/
-int schedule_on_each_cpu(work_func_t func)
+int schedule_on_cpu_mask(work_func_t func, const struct cpumask *mask)
{
int cpu;
struct work_struct __percpu *works;
@@ -2981,24 +2982,40 @@ int schedule_on_each_cpu(work_func_t func)
if (!works)
return -ENOMEM;

- get_online_cpus();
-
- for_each_online_cpu(cpu) {
+ for_each_cpu(cpu, mask) {
struct work_struct *work = per_cpu_ptr(works, cpu);

INIT_WORK(work, func);
schedule_work_on(cpu, work);
}

- for_each_online_cpu(cpu)
+ for_each_cpu(cpu, mask)
flush_work(per_cpu_ptr(works, cpu));

- put_online_cpus();
free_percpu(works);
return 0;
}

/**
+ * schedule_on_each_cpu - execute a function synchronously on each online CPU
+ * @func: the function to call
+ *
+ * schedule_on_each_cpu() executes @func on each online CPU using the
+ * system workqueue and blocks until all CPUs have completed.
+ * schedule_on_each_cpu() is very slow.
+ *
+ * RETURNS:
+ * 0 on success, -errno on failure.
+ */
+int schedule_on_each_cpu(work_func_t func)
+{
+ get_online_cpus();
+ schedule_on_cpu_mask(func, cpu_online_mask);
+ put_online_cpus();
+ return 0;
+}
+
+/**
* flush_scheduled_work - ensure that any scheduled work has run to completion.
*
* Forces execution of the kernel-global workqueue and blocks until its
diff --git a/mm/swap.c b/mm/swap.c
index 4a1d0d2..d4a862b 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -405,6 +405,11 @@ static void activate_page_drain(int cpu)
pagevec_lru_move_fn(pvec, __activate_page, NULL);
}

+static bool need_activate_page_drain(int cpu)
+{
+ return pagevec_count(&per_cpu(activate_page_pvecs, cpu)) != 0;
+}
+
void activate_page(struct page *page)
{
if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
@@ -422,6 +427,11 @@ static inline void activate_page_drain(int cpu)
{
}

+static bool need_activate_page_drain(int cpu)
+{
+ return false;
+}
+
void activate_page(struct page *page)
{
struct zone *zone = page_zone(page);
@@ -683,7 +693,32 @@ static void lru_add_drain_per_cpu(struct work_struct *dummy)
*/
int lru_add_drain_all(void)
{
- return schedule_on_each_cpu(lru_add_drain_per_cpu);
+ cpumask_var_t mask;
+ int cpu, rc;
+
+ if (!alloc_cpumask_var(&mask, GFP_KERNEL))
+ return -ENOMEM;
+ cpumask_clear(mask);
+
+ /*
+ * Figure out which cpus need flushing. It's OK if we race
+ * with changes to the per-cpu lru pvecs, since it's no worse
+ * than if we flushed all cpus, since a cpu could still end
+ * up putting pages back on its pvec before we returned.
+ * And this avoids interrupting other cpus unnecessarily.
+ */
+ for_each_online_cpu(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))
+ cpumask_set_cpu(cpu, mask);
+ }
+
+ rc = schedule_on_cpu_mask(lru_add_drain_per_cpu, mask);
+
+ free_cpumask_var(mask);
+ return rc;
}

/*
--
1.8.3.1


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