linux-kernel - Re: [PATCH memcg v4] net: set proper memcg for net

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Message-ID: <20220427122232.GA9823@blackbody.suse.cz>
Date:   Wed, 27 Apr 2022 14:22:32 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Vasily Averin <vvs@...nvz.org>, Vlastimil Babka <vbabka@...e.cz>,
        Roman Gushchin <roman.gushchin@...ux.dev>, kernel@...nvz.org,
        Florian Westphal <fw@...len.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>,
        Cgroups <cgroups@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH memcg v4] net: set proper memcg for net_init hooks
 allocations

On Tue, Apr 26, 2022 at 10:23:32PM -0700, Shakeel Butt <shakeelb@...gle.com> wrote:
> [...]
> >
> > +static inline struct mem_cgroup *get_mem_cgroup_from_obj(void *p)
> > +{
> > +       struct mem_cgroup *memcg;
> > +
> 
> Do we need memcg_kmem_enabled() check here or maybe
> mem_cgroup_from_obj() should be doing memcg_kmem_enabled() instead of
> mem_cgroup_disabled() as we can have "cgroup.memory=nokmem" boot
> param.

I reckon such a guard is on the charge side and readers should treat
NULL and root_mem_group equally. Or is there a case when these two are
different? 

(I can see it's different semantics when stored in current->active_memcg
(and active_memcg() getter) but for such "outer" callers like here it
seems equal.)

Regards,
Michal