Re: [PATCH memcg v3] net: set proper memcg for net_init hooks allocations

From: Vasily Averin <vvs@openvz.org>
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>
Subject: Re: [PATCH memcg v3] net: set proper memcg for net_init hooks allocations
Date: Tue, 26 Apr 2022 08:58:07 +0300	[thread overview]
Message-ID: <a153e5da-b22a-2ea5-f0ef-a46337711400@openvz.org> (raw)
In-Reply-To: <YmdeCqi6wmgiSiWh@carbon>

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