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From:   Waiman Long <llong@redhat.com>
Subject: Re: [PATCH 2/3] mm, memcg: Remove obsolete memcg_free_kmem()
To:     Roman Gushchin <guro@fb.com>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>, linux-kernel@vger.kernel.org,
        cgroups@vger.kernel.org, linux-mm@kvack.org,
        Shakeel Butt <shakeelb@google.com>,
        Muchun Song <songmuchun@bytedance.com>
References: <20211001190938.14050-1-longman@redhat.com>
 <20211001190938.14050-3-longman@redhat.com>
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Message-ID: <b45fd235-a454-360e-4853-d41db3213e9d@redhat.com>
Date:   Fri, 1 Oct 2021 22:03:05 -0400
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On 10/1/21 8:01 PM, Roman Gushchin wrote:
> On Fri, Oct 01, 2021 at 03:09:37PM -0400, Waiman Long wrote:
>> Since commit d648bcc7fe65 ("mm: kmem: make memcg_kmem_enabled()
>> irreversible"), the only thing memcg_free_kmem() does is to call
>> memcg_offline_kmem() when the memcg is still online. However,
>> memcg_offline_kmem() is only called from mem_cgroup_css_free() which
>> cannot be reached if the memcg hasn't been offlined first.
> Hm, is it true? What if online_css() fails?
I just realize that memcg_online_kmem() is called at css_create(). So 
yes, if css_online() fails (i.e. ENOMEM), we will need to do 
memcg_offline_kmem().
>> As this
>> function now serves no purpose, we should just remove it.
> It looks like we can just use memcg_offline_kmem() instead of
> memcg_free_kmem().

Right, memcg_free_kmem() isn't the right name for that. I agree that we 
should just change mem_cgroup_css_free() to call memcg_offline_kmem() 
directly. Will update the patch accordingly.

Thanks,
Longman