From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx155.postini.com [74.125.245.155]) by kanga.kvack.org (Postfix) with SMTP id A3F1C6B004F for ; Mon, 5 Dec 2011 05:29:33 -0500 (EST) Message-ID: <4EDC9CE8.7090900@parallels.com> Date: Mon, 5 Dec 2011 08:28:56 -0200 From: Glauber Costa MIME-Version: 1.0 Subject: Re: [PATCH v7 00/10] Request for Inclusion: per-cgroup tcp memory pressure References: <1322611021-1730-1-git-send-email-glommer@parallels.com> <20111130111152.6b1c7366.kamezawa.hiroyu@jp.fujitsu.com> <4ED91318.1030803@parallels.com> <20111205110619.ecc538a0.kamezawa.hiroyu@jp.fujitsu.com> <4EDC8A5F.8040402@parallels.com> <20111205185108.099f393e.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20111205185108.099f393e.kamezawa.hiroyu@jp.fujitsu.com> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: KAMEZAWA Hiroyuki Cc: linux-kernel@vger.kernel.org, paul@paulmenage.org, lizf@cn.fujitsu.com, ebiederm@xmission.com, davem@davemloft.net, gthelen@google.com, netdev@vger.kernel.org, linux-mm@kvack.org, kirill@shutemov.name, avagin@parallels.com, devel@openvz.org, eric.dumazet@gmail.com, cgroups@vger.kernel.org On 12/05/2011 07:51 AM, KAMEZAWA Hiroyuki wrote: > On Mon, 5 Dec 2011 07:09:51 -0200 > Glauber Costa wrote: > >> On 12/05/2011 12:06 AM, KAMEZAWA Hiroyuki wrote: >>> On Fri, 2 Dec 2011 16:04:08 -0200 >>> Glauber Costa wrote: >>> >>>> On 11/30/2011 12:11 AM, KAMEZAWA Hiroyuki wrote: >>>>> On Tue, 29 Nov 2011 21:56:51 -0200 >>>>> Glauber Costa wrote: >>>>> >>>>>> Hi, >>>>>> >>>>>> This patchset implements per-cgroup tcp memory pressure controls. It did not change >>>>>> significantly since last submission: rather, it just merges the comments Kame had. >>>>>> Most of them are style-related and/or Documentation, but there are two real bugs he >>>>>> managed to spot (thanks) >>>>>> >>>>>> Please let me know if there is anything else I should address. >>>>>> >>>>> >>>>> After reading all codes again, I feel some strange. Could you clarify ? >>>>> >>>>> Here. >>>>> == >>>>> +void sock_update_memcg(struct sock *sk) >>>>> +{ >>>>> + /* right now 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)) >>>>> + sk->sk_cgrp = sk->sk_prot->proto_cgroup(memcg); >>>>> + rcu_read_unlock(); >>>>> == >>>>> >>>>> sk->sk_cgrp is set to a memcg without any reference count. >>>>> >>>>> Then, no check for preventing rmdir() and freeing memcgroup. >>>>> >>>>> Is there some css_get() or mem_cgroup_get() somewhere ? >>>>> >>>> >>>> There were a css_get in the first version of this patchset. It was >>>> removed, however, because it was deemed anti-intuitive to prevent rmdir, >>>> since we can't know which sockets are blocking it, or do anything about >>>> it. Or did I misunderstand something ? >>>> >>> >>> Maybe I misuderstood. Thank you. Ok, there is no css_get/put and >>> rmdir() is allowed. But, hmm....what's guarding threads from stale >>> pointer access ? >>> >>> Does a memory cgroup which is pointed by sk->sk_cgrp always exist ? >>> >> If I am not mistaken, yes, it will. (Ok, right now it won't) >> >> Reason is a cgroup can't be removed if it is empty. >> To make it empty, you need to move the tasks away. >> >> So the sockets will be moved away as well when you do it. So right now >> they are not, so it would then probably be better to increase a >> reference count with a comment saying that it is temporary. >> > > I'm sorry if I misunderstand. > > At task exit, __fput() will be called against file descriptors, yes. > __fput() calles f_op->release() => inet_release() => tcp_close(). > > But TCP socket may be alive after task exit until it gets down to > protocol close. For example, until the all message in send buffer > is acked, socket and tcp connection will not be disappear. > > In short, socket's lifetime is different from it's task's. > So, there may be sockets which are not belongs to any task. > Yeah, you're right. I guess this is one more reason for us to just keep the memcg reference around. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org