From mboxrd@z Thu Jan 1 00:00:00 1970 From: Glauber Costa Subject: Re: [PATCH v3 06/13] memcg: kmem controller infrastructure Date: Fri, 28 Sep 2012 15:34:19 +0400 Message-ID: <50658B3B.9020303@parallels.com> References: <1347977050-29476-1-git-send-email-glommer@parallels.com> <1347977050-29476-7-git-send-email-glommer@parallels.com> <20120926155108.GE15801@dhcp22.suse.cz> <5064392D.5040707@parallels.com> <20120927134432.GE29104@dhcp22.suse.cz> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20120927134432.GE29104-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Michal Hocko Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org, devel-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org, Tejun Heo , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Suleiman Souhlal , Frederic Weisbecker , Mel Gorman , David Rientjes , Christoph Lameter , Pekka Enberg , Johannes Weiner On 09/27/2012 05:44 PM, Michal Hocko wrote: >> > the reference count aquired by mem_cgroup_get will still prevent the >> > memcg from going away, no? > Yes but you are outside of the rcu now and we usually do css_get before > we rcu_unlock. mem_cgroup_get just makes sure the group doesn't get > deallocated but it could be gone before you call it. Or I am just > confused - these 2 levels of ref counting is really not nice. > > Anyway, I have just noticed that __mem_cgroup_try_charge does > VM_BUG_ON(css_is_removed(&memcg->css)) on a given memcg so you should > keep css ref count up as well. > IIRC, css_get will prevent the cgroup directory from being removed. Because some allocations are expected to outlive the cgroup, we specifically don't want that.