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Subject[PATCH 4.4 047/131] vmstat: make vmstat_updater deferrable again and shut down on idle
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

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

[ Upstream commit 0eb77e9880321915322d42913c3b53241739c8aa ]

Currently the vmstat updater is not deferrable as a result of commit
ba4877b9ca51 ("vmstat: do not use deferrable delayed work for
vmstat_update"). This in turn can cause multiple interruptions of the
applications because the vmstat updater may run at

Make vmstate_update deferrable again and provide a function that folds
the differentials when the processor is going to idle mode thus
addressing the issue of the above commit in a clean way.

Note that the shepherd thread will continue scanning the differentials
from another processor and will reenable the vmstat workers if it
detects any changes.

Fixes: ba4877b9ca51 ("vmstat: do not use deferrable delayed work for vmstat_update")
Signed-off-by: Christoph Lameter <cl@linux.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/vmstat.h | 2 ++
kernel/sched/idle.c | 1 +
mm/vmstat.c | 69 +++++++++++++++++++++++++++---------------
3 files changed, 47 insertions(+), 25 deletions(-)

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 3e5d9075960f..73fae8c4a5fb 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -189,6 +189,7 @@ extern void __inc_zone_state(struct zone *, enum zone_stat_item);
extern void dec_zone_state(struct zone *, enum zone_stat_item);
extern void __dec_zone_state(struct zone *, enum zone_stat_item);

+void quiet_vmstat(void);
void cpu_vm_stats_fold(int cpu);
void refresh_zone_stat_thresholds(void);

@@ -249,6 +250,7 @@ static inline void __dec_zone_page_state(struct page *page,

static inline void refresh_zone_stat_thresholds(void) { }
static inline void cpu_vm_stats_fold(int cpu) { }
+static inline void quiet_vmstat(void) { }

static inline void drain_zonestat(struct zone *zone,
struct per_cpu_pageset *pset) { }
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index bfd573122e0d..306a859b36f0 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -219,6 +219,7 @@ static void cpu_idle_loop(void)
*/

__current_set_polling();
+ quiet_vmstat();
tick_nohz_idle_enter();

while (!need_resched()) {
diff --git a/mm/vmstat.c b/mm/vmstat.c
index a2d70ef74db7..6af9bbad94c7 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -460,7 +460,7 @@ static int fold_diff(int *diff)
*
* The function returns the number of global counters updated.
*/
-static int refresh_cpu_vm_stats(void)
+static int refresh_cpu_vm_stats(bool do_pagesets)
{
struct zone *zone;
int i;
@@ -484,33 +484,35 @@ static int refresh_cpu_vm_stats(void)
#endif
}
}
- cond_resched();
#ifdef CONFIG_NUMA
- /*
- * Deal with draining the remote pageset of this
- * processor
- *
- * Check if there are pages remaining in this pageset
- * if not then there is nothing to expire.
- */
- if (!__this_cpu_read(p->expire) ||
+ if (do_pagesets) {
+ cond_resched();
+ /*
+ * Deal with draining the remote pageset of this
+ * processor
+ *
+ * Check if there are pages remaining in this pageset
+ * if not then there is nothing to expire.
+ */
+ if (!__this_cpu_read(p->expire) ||
!__this_cpu_read(p->pcp.count))
- continue;
+ continue;

- /*
- * We never drain zones local to this processor.
- */
- if (zone_to_nid(zone) == numa_node_id()) {
- __this_cpu_write(p->expire, 0);
- continue;
- }
+ /*
+ * We never drain zones local to this processor.
+ */
+ if (zone_to_nid(zone) == numa_node_id()) {
+ __this_cpu_write(p->expire, 0);
+ continue;
+ }

- if (__this_cpu_dec_return(p->expire))
- continue;
+ if (__this_cpu_dec_return(p->expire))
+ continue;

- if (__this_cpu_read(p->pcp.count)) {
- drain_zone_pages(zone, this_cpu_ptr(&p->pcp));
- changes++;
+ if (__this_cpu_read(p->pcp.count)) {
+ drain_zone_pages(zone, this_cpu_ptr(&p->pcp));
+ changes++;
+ }
}
#endif
}
@@ -1393,7 +1395,7 @@ static cpumask_var_t cpu_stat_off;

static void vmstat_update(struct work_struct *w)
{
- if (refresh_cpu_vm_stats()) {
+ if (refresh_cpu_vm_stats(true)) {
/*
* Counters were updated so we expect more updates
* to occur in the future. Keep on running the
@@ -1424,6 +1426,23 @@ static void vmstat_update(struct work_struct *w)
}
}

+/*
+ * Switch off vmstat processing and then fold all the remaining differentials
+ * until the diffs stay at zero. The function is used by NOHZ and can only be
+ * invoked when tick processing is not active.
+ */
+void quiet_vmstat(void)
+{
+ if (system_state != SYSTEM_RUNNING)
+ return;
+
+ do {
+ if (!cpumask_test_and_set_cpu(smp_processor_id(), cpu_stat_off))
+ cancel_delayed_work(this_cpu_ptr(&vmstat_work));
+
+ } while (refresh_cpu_vm_stats(false));
+}
+
/*
* Check if the diffs for a certain cpu indicate that
* an update is needed.
@@ -1456,7 +1475,7 @@ static bool need_update(int cpu)
*/
static void vmstat_shepherd(struct work_struct *w);

-static DECLARE_DELAYED_WORK(shepherd, vmstat_shepherd);
+static DECLARE_DEFERRABLE_WORK(shepherd, vmstat_shepherd);

static void vmstat_shepherd(struct work_struct *w)
{
--
2.19.1


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