linux-kernel - Re: [PATCH net-next v5 2/3] sock: Always take memcg pressure into consideration

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Message-ID: <20230602204159.vo7fmuvh3y2pdfi5@google.com>
Date:   Fri, 2 Jun 2023 20:41:59 +0000
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Abel Wu <wuyun.abel@...edance.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Simon Horman <simon.horman@...igine.com>,
        netdev@...r.kernel.org, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>
Subject: Re: [PATCH net-next v5 2/3] sock: Always take memcg pressure into consideration

+Willem

On Fri, Jun 02, 2023 at 04:11:34PM +0800, Abel Wu wrote:
> The sk_under_memory_pressure() is called to check whether there is
> memory pressure related to this socket. But now it ignores the net-
> memcg's pressure if the proto of the socket doesn't care about the
> global pressure, which may put burden on its memcg compaction or
> reclaim path (also remember that socket memory is un-reclaimable).
> 
> So always check the memcg's vm status to alleviate memstalls when
> it's in pressure.
> 

This is interesting. UDP is the only protocol which supports memory
accounting (i.e. udp_memory_allocated) but it does not define
memory_pressure. In addition, it does have sysctl_udp_mem. So
effectively UDP supports a hard limit and ignores memcg pressure at the
moment. This patch will change its behavior to consider memcg pressure
as well. I don't have any objection but let's get opinion of UDP
maintainer.

> Signed-off-by: Abel Wu <wuyun.abel@...edance.com>
> ---
>  include/net/sock.h | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 3f63253ee092..ad1895ffbc4a 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -1411,13 +1411,11 @@ static inline bool sk_has_memory_pressure(const struct sock *sk)
>  
>  static inline bool sk_under_memory_pressure(const struct sock *sk)
>  {
> -	if (!sk->sk_prot->memory_pressure)
> -		return false;
> -
>  	if (mem_cgroup_under_socket_pressure(sk->sk_memcg))
>  		return true;
>  
> -	return !!*sk->sk_prot->memory_pressure;
> +	return sk->sk_prot->memory_pressure &&
> +		*sk->sk_prot->memory_pressure;
>  }
>  
>  static inline long
> -- 
> 2.37.3
>