Re: [PATCH v2] memcg: net: track network throttling due to memcg memory pressure

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 16 Oct 2025 09:10:35 -0700 Shakeel Butt <shakeel.butt@linux.dev> wrote:

> The kernel can throttle network sockets if the memory cgroup associated
> with the corresponding socket is under memory pressure. The throttling
> actions include clamping the transmit window, failing to expand receive
> or send buffers, aggressively prune out-of-order receive queue, FIN
> deferred to a retransmitted packet and more. Let's add memcg metric to
> indicate track such throttling actions.
> 
> At the moment memcg memory pressure is defined through vmpressure and in
> future it may be defined using PSI or we may add more flexible way for
> the users to define memory pressure, maybe through ebpf. However the
> potential throttling actions will remain the same, so this newly
> introduced metric will continue to track throttling actions irrespective
> of how memcg memory pressure is defined.
> 
> ...
>
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -2635,8 +2635,12 @@ static inline bool mem_cgroup_sk_under_memory_pressure(const struct sock *sk)
>  #endif /* CONFIG_MEMCG_V1 */
>  
>  	do {
> -		if (time_before64(get_jiffies_64(), mem_cgroup_get_socket_pressure(memcg)))
> +		if (time_before64(get_jiffies_64(),
> +				  mem_cgroup_get_socket_pressure(memcg))) {
> +			memcg_memory_event(mem_cgroup_from_sk(sk),
> +					   MEMCG_SOCK_THROTTLED);
>  			return true;
> +		}
>  	} while ((memcg = parent_mem_cgroup(memcg)));
>  

Totally OT, but that's one bigass inlined function.  A quick test
indicates that uninlining just this function reduces the size of
tcp_input.o and tcp_output.o nicely.  x86_64 defconfig:

   text	   data	    bss	    dec	    hex	filename
  52130	   1686	      0	  53816	   d238	net/ipv4/tcp_input.o
  32335	   1221	      0	  33556	   8314	net/ipv4/tcp_output.o

   text	   data	    bss	    dec	    hex	filename
  51346	   1494	      0	  52840	   ce68	net/ipv4/tcp_input.o
  31911	   1125	      0	  33036	   810c	net/ipv4/tcp_output.o