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

[Shakeel Butt]

+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@xxxxxxxxxxxxx>
> ---
>  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
>