linux-kernel - Re: [PATCH v8 4/8] mm: Provide a new count_objcg

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Message-ID: <3dd5dadf-824c-4a28-a133-9967027c45f3@linux.dev>
Date: Sat, 28 Sep 2024 13:46:04 +0800
From: Chengming Zhou <chengming.zhou@...ux.dev>
To: Yosry Ahmed <yosryahmed@...gle.com>,
 Kanchana P Sridhar <kanchana.p.sridhar@...el.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, hannes@...xchg.org,
 nphamcs@...il.com, usamaarif642@...il.com, shakeel.butt@...ux.dev,
 ryan.roberts@....com, ying.huang@...el.com, 21cnbao@...il.com,
 akpm@...ux-foundation.org, nanhai.zou@...el.com, wajdi.k.feghali@...el.com,
 vinodh.gopal@...el.com
Subject: Re: [PATCH v8 4/8] mm: Provide a new count_objcg_events() API for
 batch event updates.

On 2024/9/28 11:02, Yosry Ahmed wrote:
> On Fri, Sep 27, 2024 at 7:16 PM Kanchana P Sridhar
> <kanchana.p.sridhar@...el.com> wrote:
>>
>> With the introduction of zswap_store() swapping out large folios,
>> we need to efficiently update the objcg's memcg events once per
>> successfully stored folio. For instance, the 'ZSWPOUT' event needs
>> to be incremented by folio_nr_pages().
>>
>> Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@...el.com>
>> ---
>>   include/linux/memcontrol.h | 20 ++++++++++++++++++++
>>   1 file changed, 20 insertions(+)
>>
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index 15c2716f9aa3..f47fd00c5eea 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -1778,6 +1778,21 @@ static inline void count_objcg_event(struct obj_cgroup *objcg,
>>          rcu_read_unlock();
>>   }
>>
>> +static inline void count_objcg_events(struct obj_cgroup *objcg,
>> +                                     enum vm_event_item idx,
>> +                                     unsigned long count)
>> +{
>> +       struct mem_cgroup *memcg;
>> +
>> +       if (!memcg_kmem_online())
>> +               return;
>> +
>> +       rcu_read_lock();
>> +       memcg = obj_cgroup_memcg(objcg);
>> +       count_memcg_events(memcg, idx, count);
>> +       rcu_read_unlock();
>> +}
> 
> Instead of replicating the code in count_objcg_event(), we should
> change count_objcg_event() to become count_objcg_events() (i.e. add a
> count parameter). The existing callers can pass in 1, there's only 3
> of them anyway (2 after patch 6), and they are all in zswap.

Right, agree.

> 
>> +
>>   #else
>>   static inline bool mem_cgroup_kmem_disabled(void)
>>   {
>> @@ -1834,6 +1849,11 @@ static inline void count_objcg_event(struct obj_cgroup *objcg,
>>   {
>>   }
>>
>> +static inline void count_objcg_events(struct obj_cgroup *objcg,
>> +                                     enum vm_event_item idx,
>> +                                     unsigned long count)
>> +{
>> +}
>>   #endif /* CONFIG_MEMCG */
>>
>>   #if defined(CONFIG_MEMCG) && defined(CONFIG_ZSWAP)
>> --
>> 2.27.0
>>