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From:   Waiman Long <llong@redhat.com>
Subject: Re: [PATCH v4 1/5] mm/memcg: Move mod_objcg_state() to memcontrol.c
To:     Johannes Weiner <hannes@cmpxchg.org>,
        Waiman Long <llong@redhat.com>
Cc:     Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Vlastimil Babka <vbabka@suse.cz>, Roman Gushchin <guro@fb.com>,
        linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
        linux-mm@kvack.org, Shakeel Butt <shakeelb@google.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Alex Shi <alex.shi@linux.alibaba.com>,
        Chris Down <chris@chrisdown.name>,
        Yafang Shao <laoar.shao@gmail.com>,
        Wei Yang <richard.weiyang@gmail.com>,
        Masayoshi Mizuma <msys.mizuma@gmail.com>,
        Xing Zhengjun <zhengjun.xing@linux.intel.com>,
        Matthew Wilcox <willy@infradead.org>
References: <20210419000032.5432-1-longman@redhat.com>
 <20210419000032.5432-2-longman@redhat.com> <YH2eT+JCII48hX80@cmpxchg.org>
 <ffb5705e-8629-808d-9d09-0c9c7f509326@redhat.com>
 <140444ea-14e7-b305-910f-f23fafe45488@redhat.com>
 <YH26RrMBOxLaMg4l@cmpxchg.org>
Message-ID: <b7c8e209-3311-609b-9b61-5602a89a8313@redhat.com>
Date:   Mon, 19 Apr 2021 13:19:13 -0400
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On 4/19/21 1:13 PM, Johannes Weiner wrote:
> On Mon, Apr 19, 2021 at 12:18:29PM -0400, Waiman Long wrote:
>> On 4/19/21 11:21 AM, Waiman Long wrote:
>>> On 4/19/21 11:14 AM, Johannes Weiner wrote:
>>>> On Sun, Apr 18, 2021 at 08:00:28PM -0400, Waiman Long wrote:
>>>>> The mod_objcg_state() function is moved from mm/slab.h to
>>>>> mm/memcontrol.c
>>>>> so that further optimization can be done to it in later patches without
>>>>> exposing unnecessary details to other mm components.
>>>>>
>>>>> Signed-off-by: Waiman Long <longman@redhat.com>
>>>>> ---
>>>>>    mm/memcontrol.c | 13 +++++++++++++
>>>>>    mm/slab.h       | 16 ++--------------
>>>>>    2 files changed, 15 insertions(+), 14 deletions(-)
>>>>>
>>>>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>>>>> index e064ac0d850a..dc9032f28f2e 100644
>>>>> --- a/mm/memcontrol.c
>>>>> +++ b/mm/memcontrol.c
>>>>> @@ -3150,6 +3150,19 @@ void __memcg_kmem_uncharge_page(struct
>>>>> page *page, int order)
>>>>>        css_put(&memcg->css);
>>>>>    }
>>>>>    +void mod_objcg_state(struct obj_cgroup *objcg, struct
>>>>> pglist_data *pgdat,
>>>>> +             enum node_stat_item idx, int nr)
>>>>> +{
>>>>> +    struct mem_cgroup *memcg;
>>>>> +    struct lruvec *lruvec = NULL;
>>>>> +
>>>>> +    rcu_read_lock();
>>>>> +    memcg = obj_cgroup_memcg(objcg);
>>>>> +    lruvec = mem_cgroup_lruvec(memcg, pgdat);
>>>>> +    mod_memcg_lruvec_state(lruvec, idx, nr);
>>>>> +    rcu_read_unlock();
>>>>> +}
>>>> It would be more naturally placed next to the others, e.g. below
>>>> __mod_lruvec_kmem_state().
>>>>
>>>> But no deal breaker if there isn't another revision.
>>>>
>>>> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
>>>>
>>> Yes, there will be another revision by rebasing patch series on the
>>> linux-next. I will move the function then.
>> OK, it turns out that mod_objcg_state() is only defined if
>> CONFIG_MEMCG_KMEM. That was why I put it in the CONFIG_MEMCG_KMEM block with
>> the other obj_stock functions. I think I will keep it there.
> The CONFIG_MEMCG_KMEM has become sort of useless now. It used to be
> configurable, but now it just means CONFIG_MEMCG && !CONFIG_SLOB. And
> even that doesn't make sense because while slob doesn't support slab
> object tracking, we can still do all the other stuff we do under
> KMEM. I have a patch in the works to remove the symbol and ifdefs.
>
> With that in mind, it's better to group the functions based on what
> they do rather than based on CONFIG_MEMCG_KMEM. It's easier to just
> remove another ifdef later than it is to reorder the functions.
>
OK, I will make the move then. Thanks for the explanation.

Cheers,
Longman