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

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Message-ID: <CALvZod7v0taU51TNRu=OM5iJ-bnm1ryu9shjs80PuE-SWobqFg@mail.gmail.com>
Date:   Wed, 27 Apr 2022 08:06:10 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Michal Koutný <mkoutny@...e.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 Wed, Apr 27, 2022 at 5:22 AM Michal Koutný <mkoutny@...e.com> wrote:
>
> 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.)

I was more thinking about possible shortcut optimization and unrelated
to this patch.

Vasily, can you please add documentation for get_mem_cgroup_from_obj()
similar to get_mem_cgroup_from_mm()? Also for mem_cgroup_or_root().
Please note that root_mem_cgroup can be NULL during early boot.