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    SubjectRe: [PATCH v8 3/9] socket: initial cgroup code.
    On Mon,  5 Dec 2011 19:34:57 -0200
    Glauber Costa <glommer@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@parallels.com>
    > CC: Kirill A. Shutemov <kirill@shutemov.name>
    > CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujtsu.com>
    > CC: David S. Miller <davem@davemloft.net>
    > CC: Eric W. Biederman <ebiederm@xmission.com>
    > CC: Eric Dumazet <eric.dumazet@gmail.com>

    I already replied Reviewed-by: but...


    > +/* 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 ?

    Thanks,
    -Kame




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