linux-kernel - Re: [PATCH memcg v2] memcg: accounting for objects allocated for new netdevice

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Message-ID: <YnskqRzAmtfLRd7U@carbon>
Date:   Tue, 10 May 2022 19:51:21 -0700
From:   Roman Gushchin <roman.gushchin@...ux.dev>
To:     Vasily Averin <vvs@...nvz.org>
Cc:     Shakeel Butt <shakeelb@...gle.com>, kernel@...nvz.org,
        Florian Westphal <fw@...len.de>, linux-kernel@...r.kernel.org,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>, cgroups@...r.kernel.org,
        netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH memcg v2] memcg: accounting for objects allocated for new
 netdevice

On Mon, May 02, 2022 at 03:15:51PM +0300, Vasily Averin wrote:
> Creating a new netdevice allocates at least ~50Kb of memory for various
> kernel objects, but only ~5Kb of them are accounted to memcg. As a result,
> creating an unlimited number of netdevice inside a memcg-limited container
> does not fall within memcg restrictions, consumes a significant part
> of the host's memory, can cause global OOM and lead to random kills of
> host processes.
> 
> The main consumers of non-accounted memory are:
>  ~10Kb   80+ kernfs nodes
>  ~6Kb    ipv6_add_dev() allocations
>   6Kb    __register_sysctl_table() allocations
>   4Kb    neigh_sysctl_register() allocations
>   4Kb    __devinet_sysctl_register() allocations
>   4Kb    __addrconf_sysctl_register() allocations
> 
> Accounting of these objects allows to increase the share of memcg-related
> memory up to 60-70% (~38Kb accounted vs ~54Kb total for dummy netdevice
> on typical VM with default Fedora 35 kernel) and this should be enough
> to somehow protect the host from misuse inside container.
> 
> Other related objects are quite small and may not be taken into account
> to minimize the expected performance degradation.
> 
> It should be separately mentonied ~300 bytes of percpu allocation
> of struct ipstats_mib in snmp6_alloc_dev(), on huge multi-cpu nodes
> it can become the main consumer of memory.
> 
> This patch does not enables kernfs accounting as it affects
> other parts of the kernel and should be discussed separately.
> However, even without kernfs, this patch significantly improves the
> current situation and allows to take into account more than half
> of all netdevice allocations.
> 
> Signed-off-by: Vasily Averin <vvs@...nvz.org>
> ---
> v2: 1) kernfs accounting moved into separate patch, suggested by
>     Shakeel and mkoutny@.
>     2) in ipv6_add_dev() changed original "sizeof(struct inet6_dev)"
>     to "sizeof(*ndev)", according to checkpath.pl recommendation:
>       CHECK: Prefer kzalloc(sizeof(*ndev)...) over kzalloc(sizeof
>         (struct inet6_dev)...)

It seems it's a bit too late, but just for the record:

Acked-by: Roman Gushchin <roman.gushchin@...ux.dev>

Thanks!