From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756952Ab2HUT3u (ORCPT ); Tue, 21 Aug 2012 15:29:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:1079 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756009Ab2HUT3o (ORCPT ); Tue, 21 Aug 2012 15:29:44 -0400 Date: Tue, 21 Aug 2012 22:30:31 +0300 From: "Michael S. Tsirkin" To: Rafael Aquini Cc: "Paul E. McKenney" , Peter Zijlstra , linux-mm@kvack.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Rusty Russell , Rik van Riel , Mel Gorman , Andi Kleen , Andrew Morton , Konrad Rzeszutek Wilk , Minchan Kim Subject: Re: [PATCH v8 1/5] mm: introduce a common interface for balloon pages mobility Message-ID: <20120821193031.GC9027@redhat.com> References: <1345562411.23018.111.camel@twins> <20120821162432.GG2456@linux.vnet.ibm.com> <20120821172819.GA12294@t510.redhat.com> <20120821191330.GA8324@redhat.com> <20120821192357.GD12294@t510.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120821192357.GD12294@t510.redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 21, 2012 at 04:23:58PM -0300, Rafael Aquini wrote: > On Tue, Aug 21, 2012 at 10:13:30PM +0300, Michael S. Tsirkin wrote: > > > > > > I believe rcu_dereference_protected() is what I want/need here, since this code > > > is always called for pages which we hold locked (PG_locked bit). > > > > It would only help if we locked the page while updating the mapping, > > as far as I can see we don't. > > > > But we can do it. In fact, by doing it (locking the page) we can easily avoid > the nasty race balloon_isolate_page / leak_balloon, in a much simpler way, IMHO. Absolutely. Further, we should look hard at whether most RCU uses in this patchset can be replaced with page lock. -- MST