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([2601:600:947f:f020:85dc:d2b2:c5ee:e3c4]) by smtp.gmail.com with ESMTPSA id af79cd13be357-891cefba8f0sm817018785a.40.2025.10.21.12.28.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Oct 2025 12:28:46 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: Date: Tue, 21 Oct 2025 15:28:42 -0400 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 14/33] sched/isolation: Flush memcg workqueues on cpuset isolated partition change To: Frederic Weisbecker , LKML Cc: =?UTF-8?Q?Michal_Koutn=C3=BD?= , Andrew Morton , Bjorn Helgaas , Catalin Marinas , Danilo Krummrich , "David S . Miller" , Eric Dumazet , Gabriele Monaco , Greg Kroah-Hartman , Ingo Molnar , Jakub Kicinski , Jens Axboe , Johannes Weiner , Lai Jiangshan , Marco Crivellari , Michal Hocko , Muchun Song , Paolo Abeni , Peter Zijlstra , Phil Auld , "Rafael J . Wysocki" , Roman Gushchin , Shakeel Butt , Simon Horman , Tejun Heo , Thomas Gleixner , Vlastimil Babka , Will Deacon , cgroups@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-block@vger.kernel.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, netdev@vger.kernel.org References: <20251013203146.10162-1-frederic@kernel.org> <20251013203146.10162-15-frederic@kernel.org> <364e084a-ef37-42ab-a2ae-5f103f1eb212@redhat.com> Content-Language: en-US In-Reply-To: <364e084a-ef37-42ab-a2ae-5f103f1eb212@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 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 >> Signed-off-by: Frederic Weisbecker >> --- >>   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 >>   #include >>   #include >> +#include >>   #include >>   #include >>   #include >> 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