From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx175.postini.com [74.125.245.175]) by kanga.kvack.org (Postfix) with SMTP id 94BEE6B0072 for ; Tue, 29 May 2012 12:12:19 -0400 (EDT) Date: Tue, 29 May 2012 18:11:57 +0200 From: Andrea Arcangeli Subject: Re: [PATCH 08/35] autonuma: introduce kthread_bind_node() Message-ID: <20120529161157.GE21339@redhat.com> References: <1337965359-29725-1-git-send-email-aarcange@redhat.com> <1337965359-29725-9-git-send-email-aarcange@redhat.com> <1338295753.26856.60.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1338295753.26856.60.camel@twins> Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Hillf Danton , Dan Smith , Linus Torvalds , Andrew Morton , Thomas Gleixner , Ingo Molnar , Paul Turner , Suresh Siddha , Mike Galbraith , "Paul E. McKenney" , Lai Jiangshan , Bharata B Rao , Lee Schermerhorn , Rik van Riel , Johannes Weiner , Srivatsa Vaddagiri , Christoph Lameter On Tue, May 29, 2012 at 02:49:13PM +0200, Peter Zijlstra wrote: > On Fri, 2012-05-25 at 19:02 +0200, Andrea Arcangeli wrote: > > /** > > + * kthread_bind_node - bind a just-created kthread to the CPUs of a node. > > + * @p: thread created by kthread_create(). > > + * @nid: node (might not be online, must be possible) for @k to run on. > > + * > > + * Description: This function is equivalent to set_cpus_allowed(), > > + * except that @nid doesn't need to be online, and the thread must be > > + * stopped (i.e., just returned from kthread_create()). > > + */ > > +void kthread_bind_node(struct task_struct *p, int nid) > > +{ > > + /* Must have done schedule() in kthread() before we set_task_cpu */ > > + if (!wait_task_inactive(p, TASK_UNINTERRUPTIBLE)) { > > + WARN_ON(1); > > + return; > > + } > > + > > + /* It's safe because the task is inactive. */ > > + do_set_cpus_allowed(p, cpumask_of_node(nid)); > > + p->flags |= PF_THREAD_BOUND; > > No, I've said before, this is wrong. You should only ever use > PF_THREAD_BOUND when its strictly per-cpu. Moving the your numa threads > to a different node is silly but not fatal in any way. I changed the semantics of that bitflag, now it means: userland isn't allowed to shoot itself in the foot and mess with whatever CPU bindings the kernel has set for the kernel thread. It'd be a clear regress not to set PF_THREAD_BOUND there. It would be even worse to remove the CPU binding to the node: it'd risk to copy memory with both src and dst being in remote nodes from the CPU where knuma_migrate runs on (there aren't just 2 node systems out there). -- 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