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

[Shakeel Butt <shakeel.butt@linux.dev>]

On Thu, Oct 16, 2025 at 12:46:10PM -0700, Andrew Morton wrote:
> 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
> 

Nice find and this inlining might be hurting instead of helping. I will
look into it if no one else comes to it before me.