[Devel] Re: [PATCH v8 3/9] socket: initial cgroup code.

[KAMEZAWA Hiroyuki]

On Fri, 9 Dec 2011 10:43:00 -0200
Glauber Costa <glommer at parallels.com> wrote:

> On 12/09/2011 12:05 AM, KAMEZAWA Hiroyuki wrote:
> > On Mon,  5 Dec 2011 19:34:57 -0200
> > Glauber Costa<glommer at parallels.com>  wrote:
> >
> >> The goal of this work is to move the memory pressure tcp
> >> controls to a cgroup, instead of just relying on global
> >> conditions.
> >>
> >> To avoid excessive overhead in the network fast paths,
> >> the code that accounts allocated memory to a cgroup is
> >> hidden inside a static_branch(). This branch is patched out
> >> until the first non-root cgroup is created. So when nobody
> >> is using cgroups, even if it is mounted, no significant performance
> >> penalty should be seen.
> >>
> >> This patch handles the generic part of the code, and has nothing
> >> tcp-specific.
> >>
> >> Signed-off-by: Glauber Costa<glommer at parallels.com>
> >> CC: Kirill A. Shutemov<kirill at shutemov.name>
> >> CC: KAMEZAWA Hiroyuki<kamezawa.hiroyu at jp.fujtsu.com>
> >> CC: David S. Miller<davem at davemloft.net>
> >> CC: Eric W. Biederman<ebiederm at xmission.com>
> >> CC: Eric Dumazet<eric.dumazet at gmail.com>
> >
> > I already replied Reviewed-by: but...
> Feel free. Reviews, the more, the merrier.
> 
> >
> >
> >> +/* Writing them here to avoid exposing memcg's inner layout */
> >> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
> >> +#ifdef CONFIG_INET
> >> +#include<net/sock.h>
> >> +
> >> +static bool mem_cgroup_is_root(struct mem_cgroup *memcg);
> >> +void sock_update_memcg(struct sock *sk)
> >> +{
> >> +	/* A socket spends its whole life in the same cgroup */
> >> +	if (sk->sk_cgrp) {
> >> +		WARN_ON(1);
> >> +		return;
> >> +	}
> >> +	if (static_branch(&memcg_socket_limit_enabled)) {
> >> +		struct mem_cgroup *memcg;
> >> +
> >> +		BUG_ON(!sk->sk_prot->proto_cgroup);
> >> +
> >> +		rcu_read_lock();
> >> +		memcg = mem_cgroup_from_task(current);
> >> +		if (!mem_cgroup_is_root(memcg)) {
> >> +			mem_cgroup_get(memcg);
> >> +			sk->sk_cgrp = sk->sk_prot->proto_cgroup(memcg);
> >> +		}
> >> +		rcu_read_unlock();
> >> +	}
> >> +}
> >
> > Here, you do mem_cgroup_get() if !mem_cgroup_is_root().
> >
> >
> >> +EXPORT_SYMBOL(sock_update_memcg);
> >> +
> >> +void sock_release_memcg(struct sock *sk)
> >> +{
> >> +	if (static_branch(&memcg_socket_limit_enabled)&&  sk->sk_cgrp) {
> >> +		struct mem_cgroup *memcg;
> >> +		WARN_ON(!sk->sk_cgrp->memcg);
> >> +		memcg = sk->sk_cgrp->memcg;
> >> +		mem_cgroup_put(memcg);
> >> +	}
> >> +}
> >>
> >
> > You don't check !mem_cgroup_is_root(). Hm, root memcg will not be freed
> > by this ?
> >
> No, I don't. But I check if sk->sk_cgrp is filled. So it is implied, 
> because we only fill in this value if !mem_cgroup_is_root().

Ah, ok. thank you.
-Kame