Re: [PATCH 3/8] net: consolidate memcg socket buffer tracking and accounting

Vladimir Davydov
2015-10-22T18:46:30Z

On Thu, Oct 22, 2015 at 12:21:31AM -0400, Johannes Weiner wrote:
> The tcp memory controller has extensive provisions for future memory
> accounting interfaces that won't materialize after all. Cut the code
> base down to what's actually used, now and in the likely future.
>
> - There won't be any different protocol counters in the future, so a
> direct sock->sk_memcg linkage is enough. This eliminates a lot of
> callback maze and boilerplate code, and restores most of the socket
> allocation code to pre-tcp_memcontrol state.
>
> - There won't be a tcp control soft limit, so integrating the memcg

In fact, the code is ready for the "soft" limit (I mean min, pressure,
max tuple), it just lacks a knob.

> code into the global skmem limiting scheme complicates things
> unnecessarily. Replace all that with simple and clear charge and
> uncharge calls--hidden behind a jump label--to account skb memory.
>
> - The previous jump label code was an elaborate state machine that
> tracked the number of cgroups with an active socket limit in order
> to enable the skmem tracking and accounting code only when actively
> necessary. But this is overengineered: it was meant to protect the
> people who never use this feature in the first place. Simply enable
> the branches once when the first limit is set until the next reboot.
>
...
> @@ -1136,9 +1090,6 @@ static inline bool sk_under_memory_pressure(const struct sock *sk)
> if (!sk->sk_prot->memory_pressure)
> return false;
>
> - if (mem_cgroup_sockets_enabled && sk->sk_cgrp)
> - return !!sk->sk_cgrp->memory_pressure;
> -

AFAIU, now we won't shrink the window on hitting the limit, i.e. this
patch subtly changes the behavior of the existing knobs, potentially
breaking them.

Thanks,
Vladimir