From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrea Righi Subject: Re: [RFC PATCH 5/5] refresh VM committed space after a task migration Date: Wed, 11 Jun 2008 12:37:57 +0200 (MEST) Message-ID: <484FAB04.2010800@gmail.com> References: <> <1213054383-18137-6-git-send-email-righi.andrea@gmail.com> <1213119688.13882.13.camel@nimitz> Reply-To: righi.andrea@gmail.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1213119688.13882.13.camel@nimitz> Sender: linux-kernel-owner@vger.kernel.org To: Dave Hansen Cc: balbir@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, kosaki.motohiro@jp.fujitsu.com, containers@lists.osdl.org, menage@google.com, xemul@openvz.org List-Id: containers.vger.kernel.org Dave Hansen wrote: > On Tue, 2008-06-10 at 01:33 +0200, Andrea Righi wrote: >> + preempt_disable(); >> + committed = atomic_long_read(&p->vm_committed_space); >> + atomic_long_sub(committed, &old_mem->vmacct.vm_committed_space); >> + atomic_long_add(committed, &mem->vmacct.vm_committed_space); >> + preempt_enable(); >> out: >> mmput(mm); >> } > > Why bother with the preempt stuff here? What does the actually protect > against? I assume that you're trying to keep other tasks that might run > on this CPU from seeing weird, inconsistent numbers in here. Is there > some other looks that keeps *other* cpus from seeing this? > > In any case, I think it needs a big, fat comment. Yes, true, mem_cgroup_move_task() is called after the task->cgroups pointer has been changed. So, even if task changes its committed space between the atomic_long_sub() and atomic_long_add() it will be correctly accounted in the new cgroup. -Andrea