From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Weinberger Subject: Re: [RFC][PATCH] oom: Be less verbose if the oom_control event fd has listeners Date: Thu, 05 Jun 2014 18:10:17 +0200 Message-ID: <53909669.8000007@nod.at> References: <1401976841-3899-1-git-send-email-richard@nod.at> <1401976841-3899-2-git-send-email-richard@nod.at> <20140605141841.GA23796@redhat.com> <539090F1.7090408@nod.at> <20140605160029.GA28812@redhat.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140605160029.GA28812-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Oleg Nesterov Cc: hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org, mhocko-AlSwsSmVLrQ@public.gmane.org, bsingharora-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org, akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, vdavydov-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org, tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, handai.szj-3b8fjiQLQpfQT0dZR+AlfA@public.gmane.org, rientjes-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org, kirill.shutemov-VuQAYsv1563Yd54FQh9/CA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org Am 05.06.2014 18:00, schrieb Oleg Nesterov: > On 06/05, Richard Weinberger wrote: >> >> Am 05.06.2014 16:18, schrieb Oleg Nesterov: >>> On 06/05, Richard Weinberger wrote: >>>> >>>> +int mem_cgroup_has_listeners(struct mem_cgroup *memcg) >>>> +{ >>>> + int ret = 0; >>>> + >>>> + if (!memcg) >>>> + goto out; >>>> + >>>> + spin_lock(&memcg_oom_lock); >>>> + ret = !list_empty(&memcg->oom_notify); >>>> + spin_unlock(&memcg_oom_lock); >>>> + >>>> +out: >>>> + return ret; >>>> +} >>> >>> Do we really need memcg_oom_lock to check list_empty() ? With or without >>> this lock we can race with list_add/del anyway, and I guess we do not care. >> >> Hmm, in mm/memcontrol.c all list_dev/add are under memcg_oom_lock. > > And? How this lock can help to check list_empty() ? > > list_add/del can come right after mem_cgroup_has_listeners() and change > the value of list_empty() anyway. Ahh, now I can follow your mind. :) Thanks, //richard