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Message-ID: <a01172d1-d902-4d55-bc1e-c8234985e65a@redhat.com>
Date: Tue, 21 Oct 2025 15:28:42 -0400
From: Waiman Long <llong@...hat.com>
To: Frederic Weisbecker <frederic@...nel.org>,
LKML <linux-kernel@...r.kernel.org>
Cc: Michal Koutný <mkoutny@...e.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Catalin Marinas <catalin.marinas@....com>, Danilo Krummrich
<dakr@...nel.org>, "David S . Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>, Gabriele Monaco <gmonaco@...hat.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Ingo Molnar <mingo@...hat.com>, Jakub Kicinski <kuba@...nel.org>,
Jens Axboe <axboe@...nel.dk>, Johannes Weiner <hannes@...xchg.org>,
Lai Jiangshan <jiangshanlai@...il.com>,
Marco Crivellari <marco.crivellari@...e.com>, Michal Hocko
<mhocko@...e.com>, Muchun Song <muchun.song@...ux.dev>,
Paolo Abeni <pabeni@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
Phil Auld <pauld@...hat.com>, "Rafael J . Wysocki" <rafael@...nel.org>,
Roman Gushchin <roman.gushchin@...ux.dev>,
Shakeel Butt <shakeel.butt@...ux.dev>, Simon Horman <horms@...nel.org>,
Tejun Heo <tj@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
Vlastimil Babka <vbabka@...e.cz>, Will Deacon <will@...nel.org>,
cgroups@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-block@...r.kernel.org, linux-mm@...ck.org, linux-pci@...r.kernel.org,
netdev@...r.kernel.org
Subject: Re: [PATCH 14/33] sched/isolation: Flush memcg workqueues on cpuset
isolated partition change
On 10/21/25 3:16 PM, Waiman Long wrote:
> On 10/13/25 4:31 PM, Frederic Weisbecker wrote:
>> The HK_TYPE_DOMAIN housekeeping cpumask is now modifyable at runtime. In
>> order to synchronize against memcg workqueue to make sure that no
>> asynchronous draining is still pending or executing on a newly made
>> isolated CPU, the housekeeping susbsystem must flush the memcg
>> workqueues.
>>
>> However the memcg workqueues can't be flushed easily since they are
>> queued to the main per-CPU workqueue pool.
>>
>> Solve this with creating a memcg specific pool and provide and use the
>> appropriate flushing API.
>>
>> Acked-by: Shakeel Butt <shakeel.butt@...ux.dev>
>> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
>> ---
>> include/linux/memcontrol.h | 4 ++++
>> kernel/sched/isolation.c | 2 ++
>> kernel/sched/sched.h | 1 +
>> mm/memcontrol.c | 12 +++++++++++-
>> 4 files changed, 18 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index 873e510d6f8d..001200df63cf 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -1074,6 +1074,8 @@ static inline u64 cgroup_id_from_mm(struct
>> mm_struct *mm)
>> return id;
>> }
>> +void mem_cgroup_flush_workqueue(void);
>> +
>> extern int mem_cgroup_init(void);
>> #else /* CONFIG_MEMCG */
>> @@ -1481,6 +1483,8 @@ static inline u64 cgroup_id_from_mm(struct
>> mm_struct *mm)
>> return 0;
>> }
>> +static inline void mem_cgroup_flush_workqueue(void) { }
>> +
>> static inline int mem_cgroup_init(void) { return 0; }
>> #endif /* CONFIG_MEMCG */
>> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
>> index 95d69c2102f6..9ec365dea921 100644
>> --- a/kernel/sched/isolation.c
>> +++ b/kernel/sched/isolation.c
>> @@ -144,6 +144,8 @@ int housekeeping_update(struct cpumask *mask,
>> enum hk_type type)
>> synchronize_rcu();
>> + mem_cgroup_flush_workqueue();
>> +
>> kfree(old);
>> return 0;
>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
>> index 8fac8aa451c6..8bfc0b4b133f 100644
>> --- a/kernel/sched/sched.h
>> +++ b/kernel/sched/sched.h
>> @@ -44,6 +44,7 @@
>> #include <linux/lockdep_api.h>
>> #include <linux/lockdep.h>
>> #include <linux/memblock.h>
>> +#include <linux/memcontrol.h>
>> #include <linux/minmax.h>
>> #include <linux/mm.h>
>> #include <linux/module.h>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 1033e52ab6cf..1aa14e543f35 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -95,6 +95,8 @@ static bool cgroup_memory_nokmem __ro_after_init;
>> /* BPF memory accounting disabled? */
>> static bool cgroup_memory_nobpf __ro_after_init;
>> +static struct workqueue_struct *memcg_wq __ro_after_init;
>> +
>> static struct kmem_cache *memcg_cachep;
>> static struct kmem_cache *memcg_pn_cachep;
>> @@ -1975,7 +1977,7 @@ static void schedule_drain_work(int cpu,
>> struct work_struct *work)
>> {
>> guard(rcu)();
>> if (!cpu_is_isolated(cpu))
>> - schedule_work_on(cpu, work);
>> + queue_work_on(cpu, memcg_wq, work);
>> }
>> /*
>> @@ -5092,6 +5094,11 @@ void mem_cgroup_sk_uncharge(const struct sock
>> *sk, unsigned int nr_pages)
>> refill_stock(memcg, nr_pages);
>> }
>> +void mem_cgroup_flush_workqueue(void)
>> +{
>> + flush_workqueue(memcg_wq);
>> +}
>> +
>> static int __init cgroup_memory(char *s)
>> {
>> char *token;
>> @@ -5134,6 +5141,9 @@ int __init mem_cgroup_init(void)
>> cpuhp_setup_state_nocalls(CPUHP_MM_MEMCQ_DEAD,
>> "mm/memctrl:dead", NULL,
>> memcg_hotplug_cpu_dead);
>> + memcg_wq = alloc_workqueue("memcg", 0, 0);
>
> Should we explicitly mark the memcg_wq as WQ_PERCPU even though I
> think percpu is the default. The schedule_work_on() schedules work on
> the system_percpu_wq.
According to commit dadb3ebcf39 ("workqueue: WQ_PERCPU added to
alloc_workqueue users"), the default may be changed to WQ_UNBOUND in the
future.
Cheers,
Longman
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