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    SubjectRe: [PATCH v8 3/9] socket: initial cgroup code.
    On 12/09/2011 12:05 AM, KAMEZAWA Hiroyuki wrote:
    > 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...
    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().


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