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From: Roman Gushchin <guro@fb.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>,
	"hannes@cmpxchg.org" <hannes@cmpxchg.org>,
	"vdavydov.dev@gmail.com" <vdavydov.dev@gmail.com>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"shakeelb@google.com" <shakeelb@google.com>,
	"willy@infradead.org" <willy@infradead.org>,
	"alexs@kernel.org" <alexs@kernel.org>,
	"richard.weiyang@gmail.com" <richard.weiyang@gmail.com>,
	"songmuchun@bytedance.com" <songmuchun@bytedance.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"cgroups@vger.kernel.org" <cgroups@vger.kernel.org>
Subject: Re: [PATCH 2/5] mm, memcg: narrow the scope of percpu_charge_mutex
Date: Tue, 3 Aug 2021 07:13:35 +0000	[thread overview]
Message-ID: <898130C3-FDF2-41C2-81DD-D33721C977C6@fb.com> (raw)
In-Reply-To: <YQjsHTW+46bG9XsV@dhcp22.suse.cz>

I’d go with atomic_dec().

Sent from my iPhone

> On Aug 3, 2021, at 00:11, Michal Hocko <mhocko@suse.com> wrote:
> 
> On Tue 03-08-21 14:29:13, Miaohe Lin wrote:
> [...]
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 616d1a72ece3..6210b1124929 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -2208,11 +2208,11 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
>>  */
>> static void drain_all_stock(struct mem_cgroup *root_memcg)
>> {
>> -       static DEFINE_MUTEX(percpu_charge_mutex);
>>        int cpu, curcpu;
>> +       static atomic_t drainer = ATOMIC_INIT(0);
>> 
>>        /* If someone's already draining, avoid adding running more workers. */
>> -       if (!mutex_trylock(&percpu_charge_mutex))
>> +       if (atomic_cmpxchg(&drainer, 0, 1) != 0)
>>                return;
>>        /*
>>         * Notify other cpus that system-wide "drain" is running
>> @@ -2244,7 +2244,7 @@ static void drain_all_stock(struct mem_cgroup *root_memcg)
>>                }
>>        }
>>        put_cpu();
>> -       mutex_unlock(&percpu_charge_mutex);
>> +       atomic_set(&drainer, 0);
> 
> atomic_set doesn't imply memory barrier IIRC. Is this safe?
> 
> -- 
> Michal Hocko
> SUSE Labs

  reply	other threads:[~2021-08-03  7:14 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-29 12:57 [PATCH 0/5] Cleanups and fixup for memcontrol Miaohe Lin
2021-07-29 12:57 ` [PATCH 1/5] mm, memcg: remove unused functions Miaohe Lin
2021-07-29 14:07   ` Shakeel Butt
2021-07-30  2:39   ` Muchun Song
2021-07-30  2:57   ` Roman Gushchin
2021-07-30  6:45   ` Michal Hocko
2021-07-29 12:57 ` [PATCH 2/5] mm, memcg: narrow the scope of percpu_charge_mutex Miaohe Lin
2021-07-30  2:42   ` Muchun Song
2021-07-30  3:06   ` Roman Gushchin
2021-07-30  6:50     ` Michal Hocko
2021-07-31  2:29       ` Miaohe Lin
2021-08-02  6:49         ` Michal Hocko
2021-08-02  9:54           ` Miaohe Lin
2021-08-03  3:40         ` Roman Gushchin
2021-08-03  6:29           ` Miaohe Lin
2021-08-03  7:11             ` Michal Hocko
2021-08-03  7:13               ` Roman Gushchin [this message]
2021-08-03  7:27                 ` Michal Hocko
2021-08-03  9:33             ` Muchun Song
2021-08-03 10:50               ` Miaohe Lin
2021-08-03 14:15       ` Johannes Weiner
2021-08-04  8:20         ` Michal Hocko
2021-08-05  1:44           ` Miaohe Lin
2021-07-30  6:46   ` Michal Hocko
2021-07-29 12:57 ` [PATCH 3/5] mm, memcg: save some atomic ops when flush is already true Miaohe Lin
2021-07-29 14:40   ` Shakeel Butt
2021-07-30  2:37   ` Muchun Song
2021-07-30  3:07   ` Roman Gushchin
2021-07-30  6:51   ` Michal Hocko
2021-07-29 12:57 ` [PATCH 4/5] mm, memcg: avoid possible NULL pointer dereferencing in mem_cgroup_init() Miaohe Lin
2021-07-29 13:52   ` Matthew Wilcox
2021-07-30  1:50     ` Miaohe Lin
2021-07-30  3:12   ` Roman Gushchin
2021-07-30  6:29     ` Miaohe Lin
2021-07-30  6:44     ` Michal Hocko
2021-07-31  2:05       ` Miaohe Lin
2021-08-02  6:43         ` Michal Hocko
2021-08-02 10:00           ` Miaohe Lin
2021-08-02 10:42             ` Michal Hocko
2021-08-02 11:18               ` Miaohe Lin
2021-07-29 12:57 ` [PATCH 5/5] mm, memcg: always call __mod_node_page_state() with preempt disabled Miaohe Lin
2021-07-29 14:39   ` Shakeel Butt
2021-07-30  1:52     ` Miaohe Lin
2021-07-30  2:33       ` [External] " Muchun Song
2021-07-30  2:46         ` Miaohe Lin

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