The patch titled
Subject: mm/memcg: disable migration instead of preemption in drain_all_stock()
has been added to the -mm tree. Its filename is
mm-memcg-disable-migration-instead-of-preemption-in-drain_all_stock.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-memcg-disable-migration-instead-of-preemption-in-drain_all_stock.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-memcg-disable-migration-instead-of-preemption-in-drain_all_stock.patch
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------------------------------------------------------
From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Subject: mm/memcg: disable migration instead of preemption in drain_all_stock()
Before the for-each-CPU loop, preemption is disabled so that so that
drain_local_stock() can be invoked directly instead of scheduling a
worker. Ensuring that drain_local_stock() completed on the local CPU is
not correctness problem. It _could_ be that the charging path will be
forced to reclaim memory because cached charges are still waiting for
their draining.
Disabling preemption before invoking drain_local_stock() is problematic on
PREEMPT_RT due to the sleeping locks involved. To ensure that no CPU
migrations happens across for_each_online_cpu() it is enouhg to use
migrate_disable() which disables migration and keeps context preemptible
to a sleeping lock can be acquired.
A race with CPU hotplug is not a problem because pcp data is not going
away. In the worst case we just schedule draining of an empty stock.
Use migrate_disable() instead of get_cpu() around the
for_each_online_cpu() loop.
Link: https://lkml.kernel.org/r/Yhk4UzA++ucRDwNk@xxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20220221182540.380526-7-bigeasy@xxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: kernel test robot <oliver.sang@xxxxxxxxx>
Cc: Michal Koutný <mkoutny@xxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
--- a/mm/memcontrol.c~mm-memcg-disable-migration-instead-of-preemption-in-drain_all_stock
+++ a/mm/memcontrol.c
@@ -2293,7 +2293,8 @@ static void drain_all_stock(struct mem_c
* as well as workers from this path always operate on the local
* per-cpu data. CPU up doesn't touch memcg_stock at all.
*/
- curcpu = get_cpu();
+ migrate_disable();
+ curcpu = smp_processor_id();
for_each_online_cpu(cpu) {
struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu);
struct mem_cgroup *memcg;
@@ -2316,7 +2317,7 @@ static void drain_all_stock(struct mem_c
schedule_work_on(cpu, &stock->work);
}
}
- put_cpu();
+ migrate_enable();
mutex_unlock(&percpu_charge_mutex);
}
_
Patches currently in -mm which might be from bigeasy@xxxxxxxxxxxxx are
mm-memcg-disable-threshold-event-handlers-on-preempt_rt.patch
mm-memcg-protect-per-cpu-counter-by-disabling-preemption-on-preempt_rt-where-needed.patch
mm-memcg-protect-memcg_stock-with-a-local_lock_t.patch
mm-memcg-disable-migration-instead-of-preemption-in-drain_all_stock.patch
