From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx134.postini.com [74.125.245.134]) by kanga.kvack.org (Postfix) with SMTP id AAD716B004D for ; Thu, 12 Jan 2012 10:52:40 -0500 (EST) Message-ID: <1326383551.2442.203.camel@twins> Subject: Re: [PATCH 2/2] mm: page allocator: Do not drain per-cpu lists via IPI from page allocator context From: Peter Zijlstra Date: Thu, 12 Jan 2012 16:52:31 +0100 In-Reply-To: <20120112153712.GL4118@suse.de> References: <1326276668-19932-1-git-send-email-mgorman@suse.de> <1326276668-19932-3-git-send-email-mgorman@suse.de> <1326381492.2442.188.camel@twins> <20120112153712.GL4118@suse.de> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: quoted-printable Mime-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Linux-MM , Linux-FSDevel , LKML , Andrew Morton , "Srivatsa S. Bhat" , Russell King - ARM Linux , Gilad Ben-Yossef , "Paul E. McKenney" , Miklos Szeredi , "Eric W. Biederman" , Greg KH , Gong Chen On Thu, 2012-01-12 at 15:37 +0000, Mel Gorman wrote: > On Thu, Jan 12, 2012 at 04:18:12PM +0100, Peter Zijlstra wrote: > > On Wed, 2012-01-11 at 10:11 +0000, Mel Gorman wrote: > > > At least one bug report has > > > been seen on ppc64 against a 3.0 era kernel that looked like a bug > > > receiving interrupts on a CPU being offlined.=20 > >=20 > > Got details on that Mel? The preempt_disable() in on_each_cpu() should > > serialize against the stop_machine() crap in unplug. >=20 > I might have added 2 and 2 together and got 5. >=20 > The stack trace clearly was while sending IPIs in on_each_cpu() and > always when under memory pressure and stuck in direct reclaim. This was > on !PREEMPT kernels where preempt_disable() is a no-op. That is why I > thought get_online_cpu() would be necessary. For non-preempt the required scheduling of stop_machine() will have to wait even longer. Still there might be something funny, some of the hotplug notifiers are ran before the stop_machine thing does its thing so there might be some fun interaction. -- 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