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Date:   Tue, 26 Apr 2022 08:58:07 +0300
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Subject: Re: [PATCH memcg v3] net: set proper memcg for net_init hooks
 allocations
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To:     Roman Gushchin <roman.gushchin@linux.dev>
Cc:     Vlastimil Babka <vbabka@suse.cz>,
        Shakeel Butt <shakeelb@google.com>, kernel@openvz.org,
        Florian Westphal <fw@strlen.de>, linux-kernel@vger.kernel.org,
        Michal Hocko <mhocko@suse.com>, cgroups@vger.kernel.org,
        netdev@vger.kernel.org, "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>
References: <20220424144627.GB13403@xsang-OptiPlex-9020>
 <c2f0139a-62e2-5985-34e9-d42faac81960@openvz.org> <YmdeCqi6wmgiSiWh@carbon>
From:   Vasily Averin <vvs@openvz.org>
In-Reply-To: <YmdeCqi6wmgiSiWh@carbon>
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On 4/26/22 05:50, Roman Gushchin wrote:
> On Mon, Apr 25, 2022 at 01:56:02PM +0300, Vasily Averin wrote:
>> +
>> +static inline struct mem_cgroup *get_net_memcg(void *p)
>> +{
>> +	struct mem_cgroup *memcg;
>> +
>> +	memcg = get_mem_cgroup_from_kmem(p);
>> +
>> +	if (!memcg)
>> +		memcg = root_mem_cgroup;
>> +
>> +	return memcg;
>> +}
> 
> I'm not a fan of this helper: it has nothing to do with the networking,
> actually it's a wrapper of get_mem_cgroup_from_kmem() replacing NULL
> with root_mem_cgroup.
> 
> Overall the handling of root_mem_cgroup is very messy, I don't blame
> this patch. But I wonder if it's better to simple move this code
> to the call site without introducing a new function?

Unfortunately root_mem_cgroup is defined under CONFIG_MEMCG,
so we cannot use it outside without ifdefs.

> Alternatively, you can introduce something like:
> struct mem_cgroup *mem_cgroup_or_root(struct mem_cgroup *memcg)
> {
> 	return memcg ? memcg : root_mem_cgroup;
> }

Thank you for the hint, this looks much better.
	Vasily Averin